Symposium Organizers
Maria Luisa Di Vona University of Rome Tor Vergata
Joshua Hertz University of Delaware
Philippe Knauth University of Provence
Harry L. Tuller Massachusetts Institute of Technology
B1: PEM Membranes I
Session Chairs
Monday PM, November 28, 2011
Constitution B (Sheraton)
9:30 AM - **B1.1
Disulfonated Poly(Arylene Ether) Copolymers as Proton Exchange Membranes for H2/Air and DMFC Fuel Cells.
James McGrath 1 , Yu Chen 1 , Abhishek Roy 1 , Xiang Yu 1 , Rachel VanHouten 1 , Harry Lee 1 , Ruilan Guo 1 , KwanSoo Lee 1 , Myoungbae Lee 1 , Chang Hyun Lee 1
1 Chemistry, Virginia PolyTech Inst State U, Blacksburg, Virginia, United States
Show AbstractAbout ten years ago we devised routes to prepare directly copolymerized disulfonated poly(arylene ether) random copolymers, which are often termed BPSH. The materials were quite good, but conductivity was never as high as desired. However, oxidative stability as judged by an open circuit voltage test was found to be excellent. Mechanical properties were also very good. More recently we have been investigating block copolymers that show co-continuous morphology at equal volume fractions of the hydrophilic and hydrophobic blocks, as illustrated by both AFM and TEM. These features allow for enhanced water absorption coefficients and increased conductivity. Several block and segmented copolymers were investigated and compared with random copolymer controls and various forms of Nafion. Water uptake increased with block length, and the self-diffusion coefficient of water for the block copolymers was increased relative to the random copolymers. The states of water in those ion-containing multiblocks are related to the development of well-defined, precise morphological forms. The blocks display higher conductivity than the random copolymers at comparable IEC values. The multiblock copolymers also show promise for DMFC-type membranes due to their low permeability and higher conductivity. Indeed, even for the random copolymers, it has been demonstrated that the durability of the materials exceeds 3,000 hours for portable power devices. The nanophase separation increases with block length, and the block copolymers show higher conductivity than random systems .Recent studies demonstrate the importance of annealing above the Tg of the hydrophobic phase, which apparently can assist in developing self assembly that can influence conductivity vs. relative humidity behavior. The synthesis and characterization of these materials will be discussed.REFERENCES: (1) Lee, H.S.; Roy, A; Lane, O.; Dunn, S.; McGrath, J E. Polymer (2008), 49(3), 715-723. (2) A. Roy, M.A. Hickner, X. Yu, Y. Li, T.E. Glass, J.E. McGrath. J. Polym. Sci., Pt B: Polym. Phys, 2006, 44(16), 2226. (3) M.A. Hickner, H. Ghassemi, Y.S. Kim, B. Einsla and J.E. McGrath. Chemical Reviews (2004), 104(10), 4587-4611. (4) Y.S. Kim, M.J. Sumner, W.L. Harrison, J.S. Riffle, James E. McGrath and Bryan S. Pivovar. Journal of the Electrochemical Society, 151(2) A2150-A2156 (2004). (5) W. Harrison, F. Wang, J.B. Mecham, V. Bhanu, M. Hill, Y.S. Kim, and J. E. McGrath. Journal of Polymer Science, Part A: Polymer Chemistry, (2003) Vol. 41, 2264-2276. (6) Y.S. Kim, F. Wang, M. Hickner, T.A. Zawodzinski, and J.E. McGrath. Journal of Membrane Science, 121 (1-2), 263-282 (2003). (7) Y.S. Kim, L. Dong, M. Hickner, T.E. Glass, and J.E. McGrath, Y.S. Kim, L. Dong, M. Hickner, T.E. Glass, and J.E. McGrath. Macromolecules, 36(17), 6281-6285 (2003). Lee, H.S.; Roy, A.; Lane, O.; Lee, M.; McGrath, J. E., H.S.Lee, O.Lane, M. Lee and J.E. McGrath Journal of Polymer Science, Part A: Polymer Chemistry (2010), 48(1), 214-222
10:00 AM - B1.2
Development of Novel PBI-Based Membranes as Electrolytes or HT-PEMFCs.
Eliana Quartarone 1 , Piercarlo Mustarelli 1 , Aldo Magistris 1 , Simone Angioni 1 , Pier Paolo Righetti 1
1 Dept of Chemistry, University of Pavia, Pavia Italy
Show AbstractThe current research on polymer electrolytes for fuel cells is focused on the optimization of a membrane working at about 120°C and low humidity levels (<30%), which are the real operative conditions in case of automotive applications [1]. Among the wide variety of tested polymer systems, PBI-based membranes, doped with phosphoric acid, are considered to be the best alternative to Nafion, due to their high conductivity even with no or low humidification and other promising electrochemical performances. Here, we will report on the experimental strategies followed in our laboratory in order to design better systems. First of all, new polymeric architectures, based on polybenzimida-zole, have been synthesized with an increased number of basic sites, differently interspaced along the polymer backbone [2]. Subsequently, composite membranes were prepared by dispersing in the previously prepared matrices micro- and nanosized fillers, which differ for morphology, microstructure and chemical nature [3, 4]. Finally, new monomers including oxygen and one or more sulphonic groups have been synthesized, and the consequent polymer have been prepared and tested [5]. In all cases, in situ-electrochemical tests and impedance spectroscopy were performed to evaluate the MEA performances.[1]P. Mustarelli, Fuel Cells 10, 2010, 753.[2]A. Carollo et al., J. Power Sources 160, 2006, 175.[3]P. Mustarelli et al., Advanced Materials 20, 2008, 1339.[4]E. Quartarone et al., Fuel Cells 9, 2009, 349.[5]S. Angioni et al., International Journal of Hydrogen Energy 36, 2011, 7174.
10:15 AM - B1.3
Degradation Studies on High Molecular Sulfonated Poly(ethersulfone)s and Their Blends with PBI.
Andreas Chromik 1 , Jochen Kerres 1
1 ICVT, University Stuttgart, Stuttgart, Stuttgart, Germany
Show AbstractOne of the main reasons why sulfonated poly(ethersulfone)s are still not used for fuel cell applications is their long-term stability. In this contribution enhanced synthesis concepts for high molecular weight polysulfones will be presented. The molecular weight increase is achieved by modification of well known synthesis concepts. Also ionically cross-linked membranes from this polysulfones with different polybenzimidazoles (PBI) where prepared and tested in fuel cells, to find those combinations between polymeric acid and PBI type which show the best property profile for fuel cell applications. These membranes were analysed using gel permeation chromatography (GPC) to determine the degradation of the molecular weight (distribution), and these results were compared with ex-situ membrane degradation measurements by Fenton’s test. Obtained resultsVery high molecular weights were achieved. The Molecular weight was higher than Mw=200 000, verified with light scattering measurements and dn/dc measurements, what is 2-10 times higher than molecular weights presented in literature. It is also seen that the variation of the PBI component for the ionical cross-linking affect the power density and stability of the membranes.
10:30 AM - B1.4
Phosphoric Acid Doped Cross-Linked Porous Polybenzimidazole Membranes for Proton Exchange Membrane Fuel Cells.
Cheng Hsun Shen 1 , Lien Chung Hsu 1
1 , NCKU, Tainan Taiwan
Show AbstractCross-linked porous polybenzimidazole (PBI) membranes were prepared by mixing a low-molecular-weight compound (porogen) and a crosslinker with the polymer to form cross-linked polymer membranes. SEM images of the cross-section of the porous polymer membranes show the pore size and morphology. The cross-linking by p-xylylene dichloride can effectively improve the mechanical properties of the porous PBI membranes after phosphoric acid doping. The good mechanical strength of the cross-linked porous PBI membranes makes them possible to hold more phosphoric acid, and consequently, higher proton conductivity. Fenton’s test (3% H2O2 + 4ppm FeSO4, 80oC) exhibited that covalently cross-linked groups played an important role in the radical oxidative stability of the porous membranes. The doping level of phosphoric acid in the cross-linked porous PBI membranes showed that the enhanced conductivity was due to the increase of porosity, which results in the increase of acid uptake. Impedance analysis showed that the conductivity of the cross-linked porous PBI membranes could reach 2.1 x 10 -2 S/cm at 160 oC under anhydrous condition.
10:45 AM - B1.5
Novel Azole Functional Sol-Gel Derived Inorganic-Organic Hybrid Networks as Anhydrous Proton Conducting Membranes.
Sevim Uenueguer Celik 1 , Ayhan Bozkurt 1
1 Chemistry, Fatih University, Istanbul Turkey
Show AbstractProton conducting materials have received increasing attention because of their potential applications in electrochemical devices such as polymer electrolyte membrane fuel cells (PEMFCs), hydrogen sensors, electrochromic devices (ECDs), and supercapacitor. In this work, 3-glycidoxypropyl trimethoxy silane (GPTMS) was functionalized with 1H-1,2,4-triazole (Tri), 3-aminotriazole (ATri) and 5-aminotetrazole (ATet) via ring opening of the epoxide ring and then sol-gel polymerization was performed to produce azole containing silane networks abbreviated as Si-Tri, Si-ATri and Si-ATet. In addition during sol-gel process trifluoromethane sulfonic acid (TA) was introduced into the matrix with several stoichometric ratios (TA/Azole=0.5 and 1) to produce proton conducting polymer electrolytes. FT-IR confirmed the tethering of the azole units into the silane compound and the sol-gel reaction. TGA showed that the membranes are thermally stable up to 200 oC. DSC verified the softening effect of the dopant and the homogeneity of the samples. The morphology of the membranes was investigated with SEM. The proton conductivity of these novel silane networks were studied by dielectric-impedance spectroscopy. Although proton conductivity of these membrane electrolytes depends on the acid content, the membrane without dopant produced a proton conductivity of 10-4 S/cm at 150 oC in dry state. The conductivity isotherms show Vogel–Tamman–Fulcher (VTF) behavior which implies the coupling of the charge carriers with the segmental motion of the polymer chains. A maximum proton conductivity of 1.8x10-3 S/cm was obtained for the sample Si-ATetTA1 in anhydrous condition.
11:00 AM - B1: PEM mem 1
BREAK
B2: PEM Materials I
Session Chairs
Monday PM, November 28, 2011
Constitution B (Sheraton)
11:30 AM - **B2.1
Novel Arylene Monomers, Polymers and Cross-Linked Membranes for Low- and Mid-Temperature Fuel Cells and Electrolysis.
Jochen Kerres 1
1 Institute of Chemical Process Engineering, University of Stuttgart, Stuttgart Germany
Show AbstractIn this contribution we present results on the development of novel monomers, homo-ionomers, statistical co-ionomers, block-co-ionomers and blend membranes of those polymers with different types of polybenzimidazoles. Fuel cell and electrolysis characterization results of these membranes in membrane fuel cells and membrane electrolysis are also shown.In monomer development, we focused onto the preparation of new perfluorinated arylene monomers such as pentafluorobenzene sulfonic acid, heptafluorotoluene-4-sulfonic acid, tetrafluoropyridine-4-sulfonic acid, heptafluoro-4-phosphonic acid, and octafluorobiphenyl-bisphosphonic acid.These monomers were polycondensed with different bisphenols and bisthiophenols, ending up in high-molecular polyarylene ionomers. Moreover, homopolymers, statistical copolymers and block-co-ionomers containing monomers such as disulfonated-difluorodiphenylsulfone (SDFDPS) and trisulfonated bis(4-fluorophenyl)phenylphosphinoxid (BFFPO) have been prepared, ending up in thermally highly stable arylene ionomers comprising high proton-conductivities. These different kind of polymers have been blended with different polybenzimidazoles such as PBIOO® (FumaTech) and PBI Celazol® (Celanese) both with molar excess of the sulfonated blend component for low-T membrane fuel cells (H2-PEMFC, DMFC), and HyS electrolysis, and with molar excess of the PBI blend component, followed by phosphoric acid doping, for intermediate-T fuel cells (T range from 125 to 200°C). Blend membranes were obtained which comprised high chemical and thermal stabilities as well as high proton conductivities.The membranes were applied to H2-PEMFC and DMFC at temperatures of up to 80°C (H2-PEMFC) and 130°C (DMFC), yielding good performance. In-situ degradation tests of the blend membranes in the fuel cell were performed, and the polymer degradation was determined post-mortem by gel permeation chromatography. Moreover, the membranes were applied to HyS electrolysis where SO2 electrolysis was performed in a highly concentrated aqueous H2SO4 solution of 30-60-90 wt% H2SO4. It could be seen that most of the investigated membranes (acid-excess as well as PBI-excess blend membranes) remained stable under the conditions of HyS electrolysis process as monitored by post-mortem GPC and TGA analysis. One of the membranes was applied to a HyS electrolyser, resulting in a polarization curve in the range of one recorded with a Nafion® membrane.
12:00 PM - B2.2
Proton Conductivity of SO3H-Functionalized Benzene–Periodic Mesoporous Organosilica.
Ahmad Monir Sharifi 1 2 , Michael Wark 2
1 Physical Chemistry and Electrochemistry, Leibniz Universität Hannover, Hannover Germany, 2 Ruhr-University Bochum, Laboratory of Industrial Chemistry, Bochum Germany
Show AbstractIn previous work detailed investigations of the experimental proton conductance properties and theoretical calculations concerning the effect of water content on proton transport barriers have been reported for Si-MCM-41 materials modified with functional groups within the pores for subsequent use as additives in high temperature fuel cells[1,2].The benzene-PMO material described now offers two advantages compared to Si-MCM-41; on the one hand, the organic bridges R leads to a broad spectrum of functionalities [3] that can be incorporated into the porous framework by the design of an adequate precursor and on the other hand the organic bridge R present reactive center and hence a multiplicity of reactions is possible in order to modify the PMO further with a large array of desired groups.Most effective functionalization is achieved if grafting is performed at the silica (silanol) groups as well as the benzene rings. However, as shown by XRD and neutron scattering (SANS) measurements, in general, SO3H-functionalization at the aromatic rings is more homogeneous than MPMS functionalization at silica groups, since former is kinetically hindered. Due to higher reactivity of the latter MPMS attacks most often at the first accessible group close to the pore mouths, leading to undesired pore blocking [4].The proton conductivity of benzene-PMO functionalized with sulfonic acid groups has been characterized using experimental and theoretical methods. For grafting of SO3- groups to the benzene ring a loading of 1.41 mmol H+/g is reported exceeding the best value for grafting on Si-MCM-41 found previously [2]. If grafting is performed at, both, benzene groups and silanol groups, a loading (or ion exchange capacity) of even 1.62 mmol H+/g is achieved. Due to this high content of regularly spaced proton conducting groups combined with the flexibility of the propyl spacer a drastic increase of proton conductivity compared to pristine benzene-PMO and benzene-PMO with sulfonic acid grafted via propyl chains only on silica positions is observed. The final hybrid materials exhibit high proton conductivities up to 0.2 S/cm at 100% relative humidity and 413 K [5].[1] R. Marschall, M. Sharifi, M. Wark, Micro. and Meso. Mat., 123 (2009) 21.[2] R. Marschall, J. Rathousky, M. Wark, Chem. Mater., 19 (2007) 6401.[3] S. Inagaki, S. Guan, Y. Fukushima, T. Ohsuna, O. Terasaki, J. Am. Chem. Soc., 121 (1999) 9611.[4] M. Sharifi, R. Marschall, M. Wilhelm, D. Wallacher, M. Wark, Langmuir, 27 (2011), 5516.[5] M. Sharifi, C. Köhler, P. Tölle, T. Frauenheim, M. Wark, Small 7 (2011), 1086.
12:15 PM - B2.3
Effect of Sulfonic Groups Concentration in the Properties of Novel Fluorinated Copolyamides for Use as Proton Exchange Membrane.
Luis Hernandez Ramirez 1 , Ramon Pali Casanova 1 , Carlos Flores Torres 1 , Mario Jimenez Gerónimo 1 , Manuel Aguilar Vega 2
1 Facultad de Ingenería, Universidad Autónoma del Carmen, Cd. del Carmen, Campeche, Mexico, 2 Unidad de Materiales, Centro de Investigación Científica de Yucatán A.C, Mérida, Yucatán, Mexico
Show AbstractThis work propose to study the effect that concentration of sulfonic functional group, or degree of sulfonation SD, on the structure will have on the mechanical properties and glass transition temperature, as well as in the water uptake, the ion exchange capacity IEC and the proton conductivity in a set of novel aromatic copolyamides for use as electrolyte in hydrogen- based fuel cells.Copolyamides were synthesized using Direct Polycondensation Method at high temperature, using two diamine, first one containing fluorinated groups HFDA and second one containing sulfonic groups DABS, and the aromatic chloride ISO. Properties were evaluated on casting films by comparation with performance of Nafion film, at same conditions. Flexible, transparent, and brown color film were obtained. Results indicate that by increasing molar concentration of sulfonic groups decreases mechanical performance of membrane. At 40% and 50% of degree of sulfonation, membranes become brittle, as a result of a low inherent viscosity. Water uptake capacity, ion exchange capacity IEC and proton conductivity, instead, were improved by increasing the degree of sulfonation of membranes. Comparison with Nafion revealed that the novel polyamides have improved their mechanical properties, glass transition temperature and water uptake, but ion exchange capacity IEC and proton conductivity were slightly overcome by Nafion performance.
12:45 PM - B2.5
Structure and Dynamics of Proton-Conducting Metal-Organic Frameworks.
Jamie Ford 1 2 , Jason Simmons 2 , Ryan Nieuwendaal 3 , Taner Yildirim 1 2
1 Materials Science and Engineering, University of Pennsylvania, Philadelphia, Pennsylvania, United States, 2 Center for Neutron Research, National Institute of Standards and Technology, Gaithersburg, Maryland, United States, 3 Polymer Division, National Institute of Standards and Technology, Gaithersburg, Maryland, United States
Show AbstractSulfonated polymers that host a continuous proton-conducting water microphase have become the standard materials for proton conducting membranes in fuel cells over the past decade. However, this dependence on water limits the maximum operating temperature, CO tolerance, and efficiency of the entire cell. These restrictions are lifted when water is removed from the system. Recently, metal-organic frameworks (MOFs) have received considerable attention because of their permanent porosity and inherent high surface area, particularly for gas storage applications. In addition to gas molecules, MOFs can host small molecule networks for proton conducting applications. In this case, the conducting network is independent of the MOF host, enabling more detailed study of the dynamics and mechanism of proton transport throughout the system. Here, we will present the structure, proton conductivity, and proton transport dynamics of an aluminum naphthalenedicarboxylate (Al(ndc)) MOF loaded with proton-conducting azoles, as determined with neutron powder diffraction, impedance spectroscopy, quasielastic neutron scattering, and NMR spectroscopy.
B3: Proton Conducting Ceramic Fuel Cells
Session Chairs
Monday PM, November 28, 2011
Constitution B (Sheraton)
2:30 PM - **B3.1
Getting the Most out of Doped Barium Zirconate.
Sossina Haile 1 , Yoshihiro Yamazaki 1 , Chi-Kai Yang 1
1 , Caltech, Pasadena, California, United States
Show AbstractWhen suitably processed, yttrium doped barium zirconate displays exceptionally high proton conductivity, exceeding the conductivity values of state-of-the-art oxide ion conductors at intermediate temperatures. Here we review the interrelationships between bulk transport, cation stoichiometry, proton uptake, processing and grain growth. We highlight in particular the important role of barium deficiency on the defect chemistry, as well as presenting fabrication strategies that mitigate barium loss while promoting grain growth to minimize the resistive contribution of grain boundaries. Beyond attaining reproducibly high conductivity, new data suggest that proton trapping occurs, the extent of which depends on the nature of the dopant species. Gravimetric studies furthermore suggest that weight gain at elevated temperatures under humidified conditions may be convoluted with changes in oxidation state of the host structure. Optimization of the properties through careful understanding of the connection to materials chemistry paves the way to applications in fuel cells and other electrochemical devices.
3:00 PM - B3.2
Proton-Trapping in Proton-Conducting Oxide Electrolyte for Fuel Cells: Electrochemistry and Nuclear Magnetic Resonance.
Yoshihiro Yamazaki 1 2 , Lucianne Buannic 3 , Yuji Okuyama 2 , Juan Lucio-Vega 2 , Frederic Blanc 4 , Clare Grey 3 4 , Sossina Haile 2
1 , Japan Science and Technology Agency, Tokyo, Tokyo, Japan, 2 Materials Science, California Institute of Technology, Pasadena, California, United States, 3 , Stony Brook University, Stony Brook, New York, United States, 4 , University of Cambridge, Cambridge United Kingdom
Show AbstractYttrium-doped barium zirconate has emerged as an attractive candidate for intermediate temperature solid oxide fuel cells because of its combination of high proton conductivity, exceeding the ionic conductivity state-of-the-art oxygen ion conductors, and excellent chemical stability. While recent years have seen tremendous progress in the processing of barium zirconate in order to attain reproducibly high conductivities, fundamental questions regarding the defect chemistry and proton transport mechanism remain. In particular, the possible role of proton trapping has been an open question. Here we demonstrate that trapping effects govern the proton transport in yttrium-doped barium zirconate. We determined the proton mobility and thus diffusivity using AC impedance spectroscopy in combination with thermogravimetry. At high temperatures at which such methods are unsuitable, H2/D2 exchange experiments were performed to estimate the diffusivity. The proton diffusivity curves downward in an Arrhenius plot. At high temperatures the slope corresponds to an activation energy of 17 kJ/mol, whereas at low temperatures it corresponds to a greatly increased activation energy of 45 kJ/mol. Evaluation of the curvature in the context of a trapping model implies a proton binding energy of 28 kJ/mol, where the yttrium dopant species is presumed to be the trapping site. We further probed the proton transport dynamics through high-temperature 1H solid-state nuclear magnetic resonance measurements to attain the spin-lattice relaxation time, T1. The correlation frequency for proton motion obtained by the NMR relaxation experiment, corresponds well to the jump frequency of non-trapped protons predicted from the proton-trapping model, in support of the hypothesis of extensive trapping effects. The results motivate a materials development effort aimed at lowering the binding energy to the trap site. The analysis specifically suggests that identification of a dopant with a reduced trapping energy of ~20 kJ/mol will increase the conductivity at 350 °C by a factor of ~2, enabling fuel cell operation at this temperature without resort to excessively thin electrolyte layers and specialized fabrication techniques.
3:15 PM - B3.3
Low-Temperature Protonic Conductivity in Bulk Nanometric Transition Metal Oxides Synthesized by Field Assisted Rapid Sintering.
Filippo Maglia 1 , Ilenia Tredici 1 , Monica Dapiaggi 2 , Umberto Anselmi Tamburini 1
1 Chemistry, University of Pavia, Pavia Italy, 2 Earth Science, University of Milan, Milan Italy
Show AbstractRecent investigations have evidenced that fully dense nanocrystalline oxides, such as 8 mol. % yttria stabilized zirconia and 20 mol. % gadolinium doped ceria, exhibit modifications of their transport properties when their grain size is reduced below 20-30 nm. In particular, a drastic change in the conduction mechanism was observed, evidenced by the onset of an unusually elevated conductivity in humid atmosphere for temperatures up to 150-200°C. This unprecedented conductivity was strongly dependent on the water partial pressure and showed a distinct isotopic effect, suggesting the possibility of a protonic transport mechanism in oxides otherwise characterized by the migration of the sole oxygen anions. This protonic conductivity was shown to strongly increase with reducing the grain size suggesting the possibility that nanostructure can induce drastic modification in the conduction mechanism of ceramic electrolytes. A similar, and possibly larger, effect in oxides other than the few so far investigated can be expected and must be experimentally explored. Moreover, a firm interpretation of this unusual conduction behavior is not at hand and the role played by bulk lattice defects (in particular oxygen vacancies), grain boundaries, and residual porosity on the proton conductivity needs to be further investigated. In this work we investigated the proton conduction, in wet atmosphere, of several bulk nanometric ceramics, including ceria, zirconia, alumina and titania at different values of doping with lower valence oxides. These oxides, synthesized in form of nanopowder, were densified using the high pressure field assisted sintering (HP-FARS) technique. In the HP-FARS method the densification is performed under pressures up to 1 GPa inside dies made in SiC and graphite that are heated through the passage of a high-intensity low voltage current. With this approach heating rates as high as 1000°C/min can be achieved. Thanks to the high applied pressure and the fast heating rates, full or nearly full densification is usually obtained at temperatures considerably lower than the one used in conventional sintering. Moreover, densification cycles are usually limited to few minutes. The coupling of low temperature and short duration is the key feature that allows to obtain densification with limited grain growth and/or interdiffusion.Under optimal sintering conditions grain growth was almost suppressed and it was possible to produce high density samples (relative density > 95%) with a grain size similar to that of the starting nanopowder (below 20 nm). The effect of the grain size, porosity and doping level on the proton conductivity was investigated by AC impedance under wet atmosphere in the temperature range between 50 and 400°C in the attempt to provide further information to shed light on the basic proton transport mechanism in nanometric oxides.
3:30 PM - **B3.4
Proton Conducting Ceramic Cells: Optimization of Performance and Durability Studies in Intermediate Temperature Fuel Cell: CONDOR Project.
Mathieu Marrony 1 , Julien Dailly 1 , Philippe Baranek 2 , Olivier Joubert 3 , Samuel Noirault 3 , Alexis Grimaud 4 , Fabrice Mauvy 4 , Jaouad Salmi 5 , Jonathan Deseure 6 , Gilles Taillades 7 , Jacques Roziere 7 , Eric Louradour 8
1 , European Institute for Energy Research, Karlsruhe Germany, 2 , Electricité de France, Moret-sur-Loing France, 3 IMN, University of Nantes, Nantes France, 4 ICMCB, University of Bordeaux, Pessac France, 5 , Marion Technologies, Verniolle France, 6 , LEPMI-INPG, St Martin D'Hères France, 7 ICG-AIME, University of Montpellier II, Montpellier France, 8 , Ceramiques Techniques Industrielles, Salindres France
Show AbstractProton Conducting Ceramic Fuel Cell (PCFC) has received considerable interest in recent years. This technology operating below 650°C represents one of the alternative routes in order to overcome main technological bottlenecks remained in Solid Oxide Fuel Cell (700-900°C), such as the high degradation level of cells under thermal and dynamic cycling operation and the use of costly ceramic oxide materials. CONDOR project (2009-2011) objectives were to develop advanced proton conducting ceramic fuel cells and optimize their performance in the intermediate temperature domain of operation. It was financially supported by French Government under the French National Research Agency (ANR) Program. Within a strict collaboration between French academic and industrial partners the work consisted on:- The development of advanced proton conducting electrolyte materials and highly competitive electrodes with optimized synthesis and working processes.- The physico-chemical and electrochemical characterizations of materials between 400 and 650°C of operating temperature range. Especially, the CO2 tolerance and sintering properties of cell were studied. - The scale-up of materials and their integration into a complete PCFC cell - The degradation issues and durability level of Protonic ceramic cell under various operating conditions. From this study, baseline perovskite rare earth doped barium cerate (noted BaCe0.9Y0.1O3-d) and more innovated electrolyte (BaCe0.6Y0.3Nb0.1O3-d, Ba2In2(1-x)Ti2xO5+x.1-x with x=0.2) and cathode materials (Pr2NiO4+d) have been assessed. Cell performances from 50 mW/cm2 to beyond 200 mW/cm2 have been reached in the range of 500 - 650°C of operating temperature. Long term testing in galvanostatic mode has been led during few hundred hours. Finally, critical discussion and prospective research in Proton Conducting Ceramic cells are treated.
4:00 PM - B3: PC-Ceramics
BREAK
B4: SOFC Thin Films and Surfaces
Session Chairs
Monday PM, November 28, 2011
Constitution B (Sheraton)
4:30 PM - **B4.1
Micro-Patterned Model Electrodes in SOFC- and SOEC-Related Materials Research.
Juergen Fleig 1
1 , TU Vienna, Vienna Austria
Show AbstractThin film microelectrodes or micro-patterned electrodes are powerful tools for investigating the electrochemical and chemical processes affecting and determining the polarization resistances in solid oxide fuel cells (SOFCs) or solid oxide electrolysis cells (SOECs). This is exemplified by a number of experiments on electrode- as well as electrolyte-related processes. For example, i) up to three different reaction paths of oxygen reduction were unambiguously identified and quantified for Pt electrodes on YSZ by I-V measurements, impedance spectroscopy and SIMS analysis including tracer incorporation; also the role of impurities and grain boundaries were analyzed. ii) The relation between chemical surface composition or structure and electrochemical polarization was investigated on mixed conducting oxide electrodes such as doped LaCoO3 and LaFeO3. Degradation phenomena and their relation to overpotential and gas atmosphere are discussed. iii) Micro-patterned electrodes are very advantageous when aiming at an in-depth analysis of ion conduction in thin oxides films. The effect of grain boundaries in YSZ thin films could be separated despite superimposing stray capacitances and additional structural analysis also revealed the effect of microstructure and strain on the ion conduction process in thin films.
5:00 PM - B4.2
Enhanced Oxygen Reduction Activity of Surface Modified Lanthanum Strontium Cobaltite (LSC) Epitaxial Thin Films for SOFCs.
Ethan Crumlin 1 , Eva Mutoro 1 , Sung-Jin Ahn 1 , Dongkyu Lee 1 , Michael Biegalski 2 , Hans Christen 2 , Yang Shao-Horn 1
1 Electrochemical Energy Laboratory, MIT, Cambridge, Massachusetts, United States, 2 Center of Nanophase Materials Sciences, Oak Ridge National Laboratory, Oak Ridge, Tennessee, United States
Show AbstractThe efficiency of state-of-the-art SOFCs (solid oxide fuel cells) using O2/H2 is limited by the ORR (oxygen reduction reaction) at the cathode. Advanced electrode materials with enhanced ORR activity are needed–especially for SOFC’s operating at intermediate temperatures (500-800 °C). Mixed electronic and ionic conducing perovskites, such as La1-xSrxCoO3-δ with 0 < x < 1 (LSC113) showing high oxygen ion diffusivity and surface exchange properties, are promising candidates.
We demonstrated that surface modification1,2 of LSC113 (x = 0.2) epitaxial thin films3 can strongly influence their ORR kinetics, and is thus a promising method to accelerate the ORR of SOFC cathodes: a Sr-modified (Sr(OH)2/SrCO3/SrO) LSC113 surface showed an enhanced oxygen surface exchange coefficient, kq, by 1 order of magnitude compared to unmodified epitaxial LSC113 films,2 and 1-3 orders of magnitude improvement were obtained for (La0.5Sr0.5)2CoO4±δ decorated surfaces.1 As these results suggest that a higher Sr concentration on the surface can be beneficial for fast oxygen exchange, we explore the influence of increased Sr content in the epitaxial perovskite base film (LSC113, x = 0.4) in this study. Interestingly, similar kq values were observed for unmodified LSC113 films with x = 0.2 and x = 0.4, and also for LSC214 surface modification on both different LSC base films. These results indicate that not only the film Sr concentration but also the Sr-containing surface phase impact ORR activity.
[1] E.J. Crumlin, E. Mutoro, S.-J.Ahn, G.J. la O’, D.N. Leonard, A.Borisevich, M.D. Biegalski, H.M. Christen, Y. Shao-Horn, J. Phys. Chem. Lett., 2010, 1, 3149. [2] E. Mutoro, E.J. Crumlin, M.D. Biegalski, H.M. Christen, Y. Shao-Horn, Energy Environ. Sci. 2011, in press (doi:10.1039/C1EE01245B). [3] G.J. la O’, S.J. Ahn, E. Crumlin, Y. Orikasa, M.D. Biegalski, H.M. Christen, Y. Shao-Horn, Angew. Chem. Inter. Ed., 2010, 49, 5344-5347.
5:15 PM - B4.3
Effects of Epitaxial Strain on Defect Thermodynamics in Perovskite Thin Films for Solid Oxide Fuel Cells.
Milind Gadre 1 , Yueh-Lin Lee 1 , Narasimhan Swaminathan 2 , Dane Morgan 1 2
1 Materials Science Program, University of Wisconsin-Madison, Madison, Wisconsin, United States, 2 Materials Science and Engineering, University of Wisconsin-Madison, Madison, Wisconsin, United States
Show AbstractThe efficiency of Solid Oxide Fuel Cells depends strongly on the oxygen reduction reaction (ORR) rate on the cathode. Recent studies have suggested that large enhancements in defect thermokinetics and catalytic rates may be possible through use of epitaxially strained materials. Using ab-initio methods to simulate defect energetics under epitaxial strain, we quantify the effects of strain on oxygen stoichiometry in La1-xSrxCoO3-δ (or LSC, at x=0.125) thin-films. We find at most a 2-3 fold increase in the vacancy concentration (at near 1000K) compared to bulk LSC over the range of strains from -2% (compressive) to about 4% (tensile). The results of this study suggest that epitaxial strain alone has a relatively weak effect on LSC oxygen vacancy concentration under SOFC conditions.
5:30 PM - B4.4
The Fabrication and Electrochemical Properties of Strained YSZ/GDC Thin Films.
Jun Jiang 1 , Weida Shen 2 , Joshua Hertz 2
1 Materials Science and Engineering, University of Delaware, Newark, Delaware, United States, 2 Mechanical Engineering, University of Delaware, Newark, Delaware, United States
Show AbstractSolid electrolytes are a key component in solid oxide fuel cells (SOFCs). Among the materials used as electrolytes, yttria-stabilized zirconia (YSZ) and samarium/gadolinium doped ceria (SDC/GDC) are most commonly used, due to their relative stability and moderately high ionic conductivity. Recently, a number of researchers have reported nanoscale thin films to have highly improved conductivity. The presence of interfaces and lattice strain are suggested as possible causes, but the results remain controversial and difficult to repeat. In particular, heteroepitaxial growth—especially on substrates with high lattice parameter mismatch to the film—can lead to interfacial defect structures that are strongly dependent on film thickness and other details of the deposition. Here, we report thin films of YSZ and GDC fabricated by magnetron sputtering on various substrates (Si, MgO, Al2O3, and LiAlO2,) in order to determine the effects of the substrate lattice parameter. Reactive sputtering with pure metal targets (Zr, Ce, Y, and Gd) was used for high purity and control of dopant concentration. Impedance spectroscopy-based conductivity measurements of the films will be presented, in addition to structural and chemical characterization.
5:45 PM - B4.5
Micro-Solid Oxide Fuel Cell Membrane: On the Interplay of Strain and Ionic Conductivity for Fully Crystalline to Biphasic Amorphous-Crystalline Electrolyte Films.
Jennifer Rupp 1 , Bilge Yildiz 2
1 Material Science and Engineering Department, Massachusettes Institute of Technologies, Cambridge, Massachusetts, United States, 2 Nuclear Science and Engineering Department, Massachusettes Institute of Technologies, Cambridge, Massachusetts, United States
Show AbstractToday`s micro-Solid Oxide Fuel Cells require electrolytes as thin films to allow for low ohmic resistances in electrolytes, and cell designs with less than half a micron in thickness. The overall targeted cell operation is below 700°C to assure that the micromachinable substrate support (Si, glass-ceramics) remains unharmed. However, most of the electrolyte thin films are not necessarily fully crystalline at these low processing and operation temperatures. Their electric conduction properties, as well as the overall cell performances, depend on the electrolyte microstructure, such as its degree of crystallinity, presence of strains, and grain-grain boundary ratios. Despite the importance of these microstructural traits on transport properties, it remains unclear how crystallization, strain state and ionic conductivity interplay, and an adequate model describing this interplay for standard phase pure ceria-based films is missing.In materials science, time–temperature–transformation (TTT) diagrams express the conversion rates of equal phase transformations during cooling. The most prominent materials for which TTT diagrams are used are steels, alloys, metallic-glasses, glasses, and glass-ceramics. In the first part of this presentation we will focus on the new concept of TTT-diagrams for crystallization of micro-fuel cell electrolyte films based on experimental data. Secondly, we discuss these TTT crystallization diagrams towards the new TTS-strain diagrams, which represent the strain relaxation kinetics for a given level of crystallinity. Lastly, we will demonstrate the theoretical limits of the effects of lattice strain on the ionic conductivity in crystalline ceria, primarily through the impact of strain on the energy barriers in anion migration, assessed using first principles based calculations. The relevance of these “TTT crystallization and TTS strain diagrams” is discussed with respect to the electrolyte`s ionic conductivity and predictions on the suited micro-fuel cell processing and operation conditions.
B5: Poster Session I
Session Chairs
Maria Luisa Di Vona
Joshua Hertz
Philippe Knauth
Harry Tuller
Tuesday AM, November 29, 2011
Exhibition Hall C (Hynes)
9:00 PM - B5.1
Facile Nonhydrolytic Sol-Gel Route to Mesoporous Mixed-Conducting Tungsten Oxide.
Gabriele Orsini 1 , Vincenzo Tricoli 1
1 Chemical Engineering, University of Pisa, Pisa Italy
Show AbstractMesoporous, mixed-valence tungsten oxides were synthesized by a straightforward, nonhydrolytic sol-gel method utilizing 1-butanol / tert-butanol mixtures as the gelling solvent. Composition of alcohol mixture has sensible effect on mesoporous characteristics of final product. By tuning synthesis and processing conditions specific surface area up to 140 m2/g was achieved with pore volume in excess of 0.5 cm3/g and fairly monodispersed pore-size around 18 nm. Presence of tungsten in WV-state besides WVI-state, as revealed by XPS, determines existence of oxygen vacancies in the structure. That confers important n-semiconducting characteristics upon these materials as demonstrated by EIS. Oxygen-vacancy concentration can effectively be varied by tuning conditions of thermal treatment, with strong impact on electrical properties. Electron conductivity of c.a. 20 S/cm was registered at room temperature for oxide subjected to treatment at 500°C. Upon wetting or humidification, these materials acquire also sensible proton-conduction characteristics. Proton conductivity in excess of 0.015 S/cm was measured at room temperature. As a result, these mesoporous oxides do exhibit concurrent electron and proton conduction properties under humidified conditions.Apparently, the porosity characteristics accompanied by mixed electron/proton conduction, make these materials especially appealing as conducting, mesoporous substrates utilizable in a variety of electrochemical systems, including fuel cells.
9:00 PM - B5.10
Hydration and Proton Transfer in Perfluoro Ionomers: An Ab Initio Study.
Jeffrey Clark 1 , Stephen Paddison 1
1 Chemical & Biomolecular Engineering, University of Tennessee, Knoxville, Tennessee, United States
Show AbstractElectronic structure calculations were performed to study the effects local hydration, neighboring side chain connectivity, and protogenic group separation have in facilitating proton dissociation and transfer in fragments of 3M ionomers under minimally hydrated conditions. Two different types of ionomers, each consisting of a poly(tetrafluoroethylene) (PTFE) backbone, were considered: (1) perfluorosulfonic acid (PFSA) ionomeric fragments at different equivalent weights containing two pendant side chains of distinct separation each functionalized by a terminal sulfonic acid group with chemical formula CF3CF(–O(CF2)4SO3H)(CF2)nCF(–O(CF2)4SO3H)CF3, where n = 5 and 7 which correspond to equivalent weights (EWs) of 590 and 690 grams ionomer per mole acid, respectively, and (2) imide-based fragments with multiple and distinct acid groups per side chain containing structural and chemical differences which mediated the distance separating the acidic groups; two of these were structural isomers with protogenic group separation determined by the location of a sulfonic acid group on a phenyl ring (with chemical formula CF3CF2CF(-O(CF2)4SO2(NH)SO2C6H4SO3H)CF3 with the sulfonic acid group located in either the meta or the ortho position), and a third imide-based fragment had protogenic groups separated by electron withdrawing –CF2– groups.
9:00 PM - B5.12
Fuel Cell Exhaust Treatment; High Rates of H2 + O2 Recombination by Ti0.98Pd0.02O2-δ Coated on Cordierite Monolith.
Bhaskar Mukri 1 , M. Hegde 1
1 Solid State and Structural chemistry unit, Indian Institute of Science , India, Bangalore, Karnataka, India
Show AbstractThe combustion of hydrogen gas is an exothermic reaction; its enthalpy of reaction is -286 kJ/mol. In fuel cell which utilizing H2, the exhaust should be the free from H2 for the safe environment, otherwise, it will explode. In some cases, excess H2 has to be supplied for maintain a stable voltage in electrochemical fuel cell which induces to increase unreacted H2 in exhaust gas. This problem will solve if introduce catalytic treatment on unreacted hydrogen in exhaust gas. On these criteria, we coated Ti0.98Pd0.02O2-δ catalyst on pre wash coated cordierite monolith by solution combustion method. Hydrogen and oxygen (in air) recombination reaction was carried out over catalyst( 100 mg) coated monolith inserted in fix bed reactor( quartz tube) which connected with temperature controller and in series attached a small pump to circulate the gas through reactor and one small reservoir to store the excess air. Experiment has done by injecting known amount of pure H2 gas into the excess air circulating through catalyst at space velocity, 2,550 h-1. H2 + O2 reaction occurred at room temperature with moderate rates and at higher temperature i.e.50 °C, H2 gas is combusted within 3 min in the mentioned space velocity and rate of the reaction is 36 µmoles/g/s. This catalyst is used in one of the Indian company; they succeeded 97% conversion by inserting several monoliths.References:1.S. Sharma and M. S. Hegde, ChemPhysChem, 2009, 10, 637 – 640.2.N. R. Elezovic et al., Phys. Chem. Chem. Phys., 2009, 11, 5192–5197.3.P.D. Lund et al., Int. J. Hydogen Energy, 1997, 22, 707–713.
9:00 PM - B5.13
Synthesis of Pd-Based Core-Shell Catalysts for Cathode and Anode PEMFC.
Seung Jun Hwang 1 , Sung Jong Yoo 1 , Suk-Woo Nam 1 , Tae-Hoon Lim 1 , Soo-Kil Kim 1
1 Fuel Cell Research Center, Korea Institute of Science and Technology, Seoul Korea (the Republic of)
Show AbstractThe development of low-temperature fuel cells for mobile vehicle applications has tremendously developed over several decades through experimental progress and studies of designing superior catalytic systems by computational simulation. Nonetheless, there are still many rooms for an electrocatalysis research area in proton exchange membrane fuel cells (PEMFCs): 1) overcome a sluggish kinetics and low durability of oxygen reduction reaction (ORR) with minimum amounts of Pt, 2) develop a non-Pt metal catalyst selectively reactive to hydrogen oxidation reaction (HOR) for high shut-down/startup stability. In this regard, recent interests of core-shell nanostructures have been extensively focused in the design of ORR catalysts with high activity and durability because of its structural advantages: high utilization of Pt shell and non noble core materials. To date, reports on the synthesis of Pd or Pt based core-shell nanoparticles (NPs) for the application of ORR can be classified by synthetic approach: seed mediated sequential method, galvanic-replacement reaction, and structural rearrangement technique (de-alloying or segregation). However, studies on the well defined multi-metallic core-shell nanoparticles with size below 10 nm are still relatively rare, besides it is far from certain that they could be applied to MEA single cell level. In addition, significant improvement in the design of anode materials as well as that of cathode materials also must be realized to solve the problem of cathode degradation during the shut-down/startup conditions in PEMFCs.We report herein the facile synthetic route carbon-supported Pd based core-shell NPs: PdM@Pt and Pd@PdM, designed for selectively active toward ORR and HOR respectively and single cell MEA test of their performance and durability attests to evaluate a realizable possibility. New synthetic methods were developed for monodisperse carbon supported Pd based core alloy NPs and novel chemical tools for a Pt shell deposited selectively on the core NPs. The resulting PdM@Pt catalyst has an activity of 3.37 mA/cm2 at 0.9 V (vs RHE) which is about 1.8 times higher than that of commercial 40 wt % Johnson-Matthey Pt/C catalyst with excellent stability. Also the activity of prepared Pd@PdM electrocatalysts showed better activity than that of commercial Pt/C catalyst. Also superior performance of the single cell which prepared with core-shell catalysts was explained by the in-depth study from X-ray Synchrotron and DFT calculations.
9:00 PM - B5.14
Stainless Steel Bipolar Plates Coated with Electrically Conductive CNT/ Fluorocarbon Resin Composite Film as Anticorrosion Treatment.
T. Seimiya 1 , T. Nakashima 1 , H. Kuribayashi 1 , S. Ishikawa 1 , T. Hisano 1 , D. Fukushiro 1 , K. Yoshida 1 , Y. Shishido 1 , R. Kuwabara 1 , Yoshiyuki Show 1
1 , Tokai University, Hiratsuka Japan
Show AbstractStainless steel (SS) bipolar plate for fuel cell (FC) has advantages of high manufacturability and mechanical strength. The fuel cell using the SS bipolar plates generally shows shorter lifetime than that of carbon bipolar plates, because the surface of the SS bipolar plate is corroded during the operation of fuel cell.In this presentation, eelectrically conductive composite film was formed from the carbon nanotube (CNT) and fluorocarbon resin was coated on the SS bipolar plate as anti-corrosion coating film, because both CNT and fluorocarbon resin are chemically stable materials.The CNT/fluorocarbon resin composite film was formed from dispersion fluids of the CNT and the fluorocarbon resin. CNT dispersion was made from multi-wall type CNT. Cellulose derivatives were added into water to disperse the CNT. Water based commercial fluorocarbon resin dispersion was used in this study. The dispersion fluids of the CNT and the fluorocarbon resin were mixed and stirred by applying the ultrasonic wave. The CNT/ fluorocarbon resin dispersion was applied to stainless steel bipolar plate at the thickness 50 micro meter. The bipolar plates were at 350 oC for 10min.Pure fluorocarbon resin showed the low conductivity below measuring limit. The CNT/ fluorocarbon resin composite film of 25% CNT showed high conductivity of 6S/cm. The conductivity increased up to 30S/cm with an increase in the CNT concentration up to 75%. This result indicates that the CNTs form the electrical network in the material and modify the film into electrically conductive material.This film was coated on the bipolar plates of a fuel cell. The fuel cell using the bare stainless steel bipolar plates showed maximum output power of 1.7W. The bipolar plate coated with the composite film showed the maximum output power of 2.7W. Impedance analyzer measurement for these FCs indicated that the composite film coating decreased the contact resistance between the bipolar plate and the MEA. Therefore, the FC fabricated with the metal bipolar plate, which is coated with the CNT/ fluorocarbon resin composite film, shows high output power. This result indicates that the CNT/ fluorocarbon resin composite film is useful for anticorrosion coating to bipolar plate of fuel cell.In this presentation, the polarization curve measurements were also carried out for SS bipolar plate coated with the CNT/ fluorocarbon resin composite film in order to characterize durability of this SS bipolar plate.
9:00 PM - B5.15
Superprotonic Conduction in LiH2PO4 as Revealed by High-Resolution Nuclear Magnetic Resonance.
Jin Jung Kweon 1 , Kyu Won Lee 1 , Do-wan Kim 1 , Hyun Jin Cho 1 , Cheol Eui Lee 1 , Kwang-Sei Lee 2
1 , Department of Physics and Institute for Nano Science, Seoul Korea (the Republic of), 2 , Department of Nano Systems Engineering, Gimhae Korea (the Republic of)
Show AbstractHydrogen-bonded proton conductors, which can be used in fuel cells in the intermediate temperature range, are recently attracting great interest. Prominent electrical conductivity of LiH2PO4 (LDP) distinguishes LDP from other KH2PO4 (KDP)-family members. We have studied charge dynamics in the hydrogen-bonded LiH2PO4 (LDP) by means of 1H, 31P, and 7Li nuclear magnetic resonance (NMR) measurements, in an attempt to understand the origin of the extraordinarily high electrical conductivity of the system. High-resolution NMR techniques enabled us to distinguish dynamics of the two different types of hydrogen bonds in the structure, with different bond lengths. It is revealed that the protonic motion, primarily associated with the longer hydrogen bond type, rather than the Li ionic motion, dictates the electrical conductivity.
9:00 PM - B5.16
Cathode Materials for Low Temperature Protonic Oxide Fuel Cells.
Matthew Sharp 1 , John Kilner 1
1 Department of Materials, Imperial College London, London United Kingdom
Show AbstractAs with solid oxide fuel cells (SOFCs) based on oxygen ion conducting electrolytes, work with protonic ceramic membrane fuel cells (PCMFCs) focuses on reducing operating temperatures. The key to achieving this temperature reduction lies in understanding the cathode processes, transport numbers of the cell components and mechanisms of proton conduction, in addition to seeking new potential materials.
The cathode processes of the protonic cell are regarded to be more complex compared with cells based on oxygen ion conducting electrolytes, and there appears to be some dispute in the literature as to the exact requirements of the cathode, and if these requirements can be met with single phase materials. In a purely proton conducting electrolyte, it would appear that the optimum cathode should be a mixed proton/electron conductor. However, as the splitting of O2 at the cathode may be a rate limiting step, there are reports of comparable performance with the more traditional mixed hole-oxide ion conductors.
Recently, attention has converged on layered perovskites as a promising new family of materials for cathode use in SOFCs. GdBaCo2O5+δ (GBCO) is one such material suggested for use on both SOFCs based on oxygen ion conducting electrolytes [1] and for PCMFCs. [2]
Analogous to previous work done to determine oxygen surface exchange (k*) and oxygen tracer exchange (D*) coefficients in GBCO, using the isotope (18O/16O) exchange depth profile (IEDP) method [3], we present our findings from determining proton surface exchange using the same method.
The same material has also been characterised electrically as part of a symmetrical electrochemical system using a BaCe0.5Zr0.3Y0.16Zn0.04 (BCZYZ) electrolyte (GBCO/BCZYZ/GBCO), by means of impedance spectroscopy measurements. GBCO has been shown to be chemically compatible with BCZYZ up to 1000 °C. The GBCO/BCZYZ/GBCO symmetrical cell was tested under dry and humid (H2O/D2O) air environments in the temperature range of 200 – 700 °C.
The microstructure of the symmetrical cells, sintered at different temperatures, has been studied using SEM, and is also presented in this work.
1.Tarancón, A., J. Peña-Martínez, D. Marrero-López, A. Morata, J.C. Ruiz-Morales, and P. Núñez, Solid State Ionics, (2008) 179 2372-2378
2.Lin, B., S. Zhang, L. Zhang, L. Bi, H. Ding, X. Liu, J. Gao, and G. Meng, Journal of Power Sources, (2008) 177 330-333
3.Tarancon, A., S.J. Skinner, R.J. Chater, F. Hernandez-Ramirez, and J.A. Kilner, Journal of Materials Chemistry, (2007) 17 3175-3181
9:00 PM - B5.17
Multicapillary Electrospray for Solid Acid Fuel Cell Electrode Fabrication.
Aron Varga 1 , Yong Hao 1 , Sossina Haile 1 , Mary Louie 2 , Konstantinos Giapis 2 , Nicholas Brunelli 2
1 Department of Materials Science and Applied Physics, California Institute of Technology, Pasadena, California, United States, 2 Department of Chemical Engineering, California Institute of Technology, Pasadena, California, United States
Show AbstractState-of-the-art solid acid fuel cells (SAFCs) incorporate CsH2PO4 as the electrolyte and composite electrodes formed of the electrolyte material, Pt as an electrocatalyst, and C as an electronic conductor. It has been shown that the electrode overpotentials in SAFCs monotonically decrease with decreasing size of the electrolyte particles in the composite electrode structure. This observation has motivated the development of an electrospray method for the creation of highly porous, interconnected fractal structures of CsH2PO4 with ~100nm feature sizes for application in SAFC electrodes. In this work we report the development of a multicapillary electrospray system, expanding on the original single capillary system, as a means of increasing the deposition rate to technologically relevant values. Here we adopt a computation-assisted experimental approach to design an optimized multicapillary electrospray system that allows high throughput while maintaining an excellent uniformity of the deposited nanostructure. More specifically, the geometrical configuration of the capillary tips was optimized via a finite element method, solving the 3-dimensional Laplace equation for electric field and equipotential surfaces with the objective of generating the most uniform electric field at the substrate. It is assumed that the Coulomb force on the highly charged aerosol particles dominates over any other force, e.g. gravitational and drag force. Hence the trajectory of the aerosol follows the electric field lines, making it the dominant parameter influencing the uniformity of the deposited nanostructure. It has been found that introduction of passive metallic pillars, placed in a ring surrounding the active capillaries, establishes a uniform electrostatic field directed toward the substrate. The best results were obtained when the length of the pillars was limited to ¾ of the length of active capillaries.Based on these calculations, we have fabricated a multicapillary electrospray apparatus with three active capillaries and nine passive pillars, arranged in an equilateral triangle geometrical footprint. The resulting electrode structures were characterized via optical and scanning electron microscopy. Significantly improved uniformity of the nanostructure was observed using the design parameters obtained via the numerical calculations, and compared to structures obtained with multijet systems not including passive pillars and/or height restrictions.
9:00 PM - B5.18
Proton Migration in Potassium-Doped Barium Phosphate.
Yong-Chan Jeong 1 , Dae-Hee Kim 1 , Byung-Kook Kim 2 , Yeong-Cheol Kim 1
1 School of Energy, Materials & Chemical Engineering, Korea University of Technology and Education, Cheonan, Chungnam, Korea (the Republic of), 2 High Temperature Energy Materials Center, Korea Institute of Science and Technology (KIST), Seoul Korea (the Republic of)
Show AbstractProton migration in potassium-doped barium phosphate (K-doped Ba3(PO4)2) was investigated using density functional theory. Four O ions formed a tetrahedron with a phosphorus ion positioned in the center. In the PO4 tetrahedron, three O ions (O1) were located in a layer perpendicular to the [001], and an O ion (O2) in the next layer. A K ion substitution for the Ba ion in the O2 layer was preferred, because it has less O ions than the Ba ion in the O1 layer. A proton preferred to be attached to the nearest O ion from K ion. The proton migration in the O1 ion layer required an overall energy barrier of 0.92 eV, which was higher than the reported experimental results (0.53-0.58 eV). On the other hand, an overall energy barrier (0.49 eV) for the proton migration in the O2 ion layer was well matched with the experimented ones.
9:00 PM - B5.19
Intra-Octahedral Proton Transfer in Undoped Barium Zirconate and Barium Cerate.
Yong-Chan Jeong 1 , Dae-Hee Kim 1 , Byung-Kook Kim 2 , Yeong-Cheol Kim 1
1 School of Energy, Materials & Chemical Engineering, Korea University of Technology and Education, Cheonan, Chungnam, Korea (the Republic of), 2 High Temperature Energy Materials Center, Korea Institute of Science and Technology (KIST), Seoul Korea (the Republic of)
Show AbstractIntra-octahedral proton transfer in undoped cubic barium zirconate (BaZrO3) and orthorhombic barium cerate (BaCeO3) was investigated using density functional theory. The Zr-O-Zr unit in cubic BaZrO3 is straight, while the Ce-O-Ce unit in orthorhombic BaCeO3 is bent, due to the bigger Ce ion than the Zr ion in the ABO3 perovskite crystal structure. O ions in the structure form interconnected octahedrons with B ions positioned in their centers and A ions positioned among the octahedrons. A proton attached to an O ion of an octahedron can transfer intra-octahedrally to a neighboring O ion that is also part of the octahedron. In BaZrO3, the proton transferred by bending the straight Zr-O-Zr unit with an energy barrier of 0.22 eV. In BaCeO3, the proton transferred by rotating the already bent Ce-O-Ce unit with an energy barrier of 0.26 eV.
9:00 PM - B5.2
Polymer Blends for Conducting Membranes.
Wenwen Huang 1 , Meng Zhao 2 , Fan Yang 2 , Kiefer Geers 3 , Lorne Farovitch 4 , Leonard James Macisco, Jr. 5 , Tyler Swob 6 , Thomas Smith 2 , Peggy Cebe 1
1 Department of Physics and Astronomy, Tufts University, Medford, Massachusetts, United States, 2 Chemistry and Microsystems Engineering, Rochester Institute of Technology, Rochester, New York, United States, 3 Biology, Gallaudet, Washington, DC, District of Columbia, United States, 4 Biomedical Engineering, Texas A&M University, College Station, Texas, United States, 5 National Technical Institute for the Deaf, Rochester Institute of Technology, Rochester, New York, United States, 6 Applied Mathematics, Rochester Institute of Technology, Rochester, New York, United States
Show AbstractWe are investigating the morphology and thermal chemical characteristics of composite films (membranes) comprised of poly(vinylidene fluoride) (PVDF) and polymers derived from ionic liquid imidazolium monomers. The potential utility of such membranes in capacitive electronic devices, especially in proton exchange membrane fuel cells (PEMFC)) is of particular interest. In the present research, the morphology, dielectric characteristics and crystalline habit of PVDF, in semicrystalline composite films comprised of PVDF and vinylimidazolium polymers was studied. In these materials, conditions such as choice of solvent, drying conditions and thermal treatment can affect the crystal phase, crystallite size, and degree of crystallinity of PVDF as well as the distribution of the minor component the vinylimidazolium polymer. PVDF imparts mechanical strength and chemical stability to the composite films, and because of its high crystal melting point (Tm > 160°C), serves to improve the high temperature stability of resulting membranes. The goal is to make a thin, high strength membrane that will exhibit substantial ionic. Thin composite films comprised of PVDF/ poly(1- ethyl-3-vinylimidazolium salts) and PVDF/poly(1-ethyl-3-methyl-4-vinylimidazolium salts) have been fabricated and the nature of the PVDF crystalline polymorph and degree of crystallinity have been evaluated as a function of the volume fraction of imidazolium polymer.
9:00 PM - B5.20
Correlation between Crystal Structures and Proton Conduction in Lanthanum Phosphates - A First Principles Study.
Kazuaki Toyoura 1 , Naoyuki Hatada 1 , Yoshitaro Nose 1 , Tetsuya Uda 1
1 Department of Materials Science and Engineering, Kyoto University, Kyoto Japan
Show AbstractRare-earth phosphates were recently reported as a class of proton conductors, particularly ortho- and poly-phosphates (LnPO4 and LnP3O9), having great potentials for high proton conductors. The crystal structures of the two compounds are largely different, which can lead to the difference in the proton conduction mechanism. In ortho-phosphates, all PO4 tetrahedra are independent, while poly-phosphates have corner-shared PO4 tetrahedra forming the infinite PO4 chains. The present study has theoretically addressed the correlation between the crystal structures and the proton conduction in rare-earth phosphates, taking lanthanum ortho- and poly-phosphates (LaPO4 and LaP3O9) as a model system.All the computational studies were based on first-principles calculations, which were performed using the projector augmented wave method implemented in the VASP code. The generalized gradient approximation parameterized by Perdew, Burke and Ernzerhof was used for the exchange-correlation term. The plane wave cutoff energy was 400 eV. The 5s, 5p, 6s, and 5d orbitals for lanthanum, 3s and 3p for P, 2s and 2p for oxygen, and 1s for hydrogen were treated as valence states. For finding proton conduction paths, first, proton sites were determined by evaluation of the potential energy surface (PES) with the fixed atomic positions and the following structural optimization. Then, proton migration paths and their energy profiles were evaluated using the nudged elastic band method.Protons generally reside around oxide ions in oxides, and both lanthanum phosphates, LaPO4 and LaP3O9, are no exception. Oxide ions are crystallographically classified into four (O1~O4) in LaPO4, and into five (O1~O5) in LaP3O9. O1 and O5 oxide ions in LaP3O9 are shared by two PO4 tetrahedra, to form infinite PO4 chains along c-axis. According to our calculations on the PES and the structural optimization, protons reside around all the oxide ions in LaPO4, while only around O3 and O4 in LaP3O9. This means protons do not prefer corner-shared oxide ions and show selective preference even in not-shared oxide ions depending on the local environment.The calculated proton conduction paths showed great difference in the conduction mechanism between the two phases. In LaPO4, protons almost isotropically migrate over a long range by way of all oxide ions, whose potential barrier height is 0.7 eV. In contrast, protons in LaP3O9 show dominant conduction along c-axis by repetition of rotations around O3 and O4 and hoppings between the rotational orbits. The potential barrier height along c-axis is 0.4 eV, which is much lower than that of conduction in ab-plane, ~ 1.0 eV.Thus the structural difference in PO4 tetrahedral network between ortho- and poly-phosphates largely affects the proton conduction mechanism. Using the same analogy, control of oxygen polyhedral network is a way to improve the proton conductivity in oxides, taking proton’s selective preference to some oxide ions into consideration.
9:00 PM - B5.21
Theoretical Calculation for Maximum Diffusion Coefficient of Proton in Barium Zirconate.
Jin-Hoon Yang 1 , Dae-Hee Kim 1 , Yong-Chan Jeong 1 , Byung-Kook Kim 2 , Yeong-Cheol Kim 1
1 School of Energy, Materials & Chemical Engineering, Korea University of Technology and Education, Cheonan, Chungnam, Korea (the Republic of), 2 High Temperature Energy Materials Center, Korea Institute of Science and Technology (KIST), Seoul Korea (the Republic of)
Show AbstractDoped barium zirconate is one of the most promising potential candidates for high-temperature proton conductors due to its high proton conductivity and sound chemical stability. A proton transfers from an oxygen ion to a neighboring oxygen ion, and rotate around an oxygen ion to migrate within the perovskite-structured materials. This proton migration mechanism, the combination of transfer and rotation, has been studied using density functional theory. There were two pathways for proton transfer, intra-transfer and inter-transfer, and their energy barriers were 0.21 and 0.71 eV, respectively. Therefore, the proton preferred the intra-transfer with the lower energy barrier than the inter-transfer. Maximum diffusion coefficient of the proton in a bulk 2×2×2 barium zirconate super cell was theoretically calculated. The maximum diffusion coefficient of the proton was obtained using a calculated attempt frequency of 5.72×1012 Hz; The value was 4.35×10-4 cm2/s, and agreed well with experimentally obtained one (10-4 cm2/s).
9:00 PM - B5.22
Optimization of Samarium Doped Ceria Nanopowder Suspension for Electrostatic Spray Deposition of Thin Film Electrolyte for Solid Oxide Fuel Cells.
Younggeul Jung 1 , Jinyi Choi 1 , Jeonghee Kim 1 , Junghoon Kim 2 , Dongwook Shin 1 2
1 Department of Fuel Cells and Hydrogen Technology, Hanyang University, Seoul Korea (the Republic of), 2 Division of Materials Science & Engineering, Hanyang University, Seoul Korea (the Republic of)
Show AbstractThe effect of different solvents, dispersants and solid loading amount on the suspension stability was investigated using sedimentation experiments. Dispersion of samarium doped ceria (SDC) nanopowder of average particle size ~20 nm in different solvent mixture along with PVB, fish oil, Triton-X and dibutyl phtalate as dispersants or binder has been studied. Well-dispersed SDC nanopowder suspensions based on Toluene/IPA with different additives were developed and characterized for electrostatic spray deposition process. In this study, anode supported SDC thin films for intermediate temperature solid oxide fuel cells (IT-SOFCs) were successfully fabricated using optimized suspensions with optimum conditions of electrostatic spray deposition. The morphologies of the prepared SDC thin films were studied by scanning electron microscopy (SEM). The electrostatic spray deposited SDC films were determined to be homogeneous, crack-free and well adherent to the anode substrate.
9:00 PM - B5.23
Spray Pyrolysis Deposition of Thin La0.6Sr0.4CoO3-δ Solid Oxide Fuel Cell Cathodes.
Zhen Yang 1 , Jaeyeon Hwang 2 3 , Thomas Ryll 1 , Ji-Won Son 2 , Michel Prestat 1 , Ludwig Gauckler 1
1 , ETHZ, Zurich Switzerland, 2 , Korean Institute of Science and Technology, Seoul Korea (the Republic of), 3 , Korea University, Seoul Korea (the Republic of)
Show AbstractSpray pyrolysis constitutes a cost-effective alternative to vacuum-based deposition techniques, such as pulsed laser deposition and chemical vapor deposition, to produce thin film SOFC components [1]. Its versatility in terms of processing parameters (e.g. deposition temperature, precursor concentration, flow rate, type of solvent) allows fabricating a large variety of films with various microstructures. In this work, nanoporous La0.6Sr0.4CoO3-δ (LSC) cathodes are sprayed on yttria-stabilized zirconia (YSZ) and gadolinium-doped ceria substrates (GDC). As-deposited layers are dense and amorphous. The desired perovskite phase, electrical conductivity and porosity develop upon annealing at ca. 600-700°C.The integration of sprayed LSC electrodes on NiO-YSZ supported SOFC will be discussed with focus on the thermomechanical stability, the LSC/YSZ chemical compatibility and the need of a GDC interlayer between YSZ and LSC. Since the oxygen reduction kinetics of the mixed ionic-electronic conducting LSC cathode is believed to be limited by the oxygen exchange at the air/perovskite interface, the effect of nanograin size and cathode thickness on the electrochemical cell performance between 500 °C and 600 °C will be reported. A SOFC power density comparison will be made between cells with sprayed LSC and cells with pulsed laser deposited LSC [2].[1] Muecke et al., Solid State Ionics 178 (2008) 1762.[2] Noh et al., Fuel Cells, 10 (2010) 1057.
9:00 PM - B5.24
Ultra-Thin Low Temperature Solid Oxide Fuel Cells and Limits on Dimensionality Reduction for Improved Performance.
Kian Kerman 1 , Bo-Kuai Lai 1 , Shriram Ramanathan 1
1 , Harvard, Cambridge, Massachusetts, United States
Show AbstractMinimizing ohmic loss across electrolytes in solid oxide fuel cells (SOFCs) operating in the low temperature regime (below 600°C) requires significant reduction of layer thickness. We have tested the ultimate limits of this reduction by creating free standing thin film SOFCs using yttria stabilized zirconia (YSZ) electrolytes and porous Pt electrodes. Stable open circuit potential has been observed for electrolytes as thin as 27 nm and performance of over 1 W/cm2 has been achieved at temperatures as low as 500°C. [1] Operation in alternative fuels, such as methane, has also been demonstrated in this temperature range. [1,2] Complexity in the morphological behavior of metallic electrodes and motivation to engineer new materials for stable low temperature SOFC applications will be discussed. References[1] K. Kerman et al. J. Power Sources 196 (2011) 2608-2614.[2] B.K. Lai et al. J. Power Sources 196 (2011) 6299-6304.
9:00 PM - B5.25
Properties of the Gadolinium Doped Ceria Self-Supported Films at the Low Temperature.
Victor Shelukhin 1 , Ilya Zon 1 , Igor Lubomirsky 1
1 Materials and Interfaces, Weizmann Institute of Science, Rehovot Israel
Show AbstractGd-doped ceria is one of the most promising oxygen ion conductors for applications in SOFCs. Despite more than three decades of studies, a number of issues related to the interplay between mechanical and electrical properties remain unknown. To elucidate this link we investigated substrate-supported and self-supported films of Au\ Ce0.8Gd0.2O1.9 (420±20 nm)\Au with impedance spectroscopy (1 Hz-1 MHz; 40-450 K). Above 120 K, both types of films have similar bulk dielectric constant, which is field-independent (no charge trapping). The grain boundary conductivity for both types of films freezes out below 150 K. Upon cooling till 40 K, the dielectric constant of the substrate-supported films decreases continuously but remains within the range of 20.5±2.0. All investigated (at least 17 samples) self-supported films exhibit small (~2%) but well detectable instability of the dielectric constant with the range 90-120 K. This instability is accompanied by the minimum of the loss tangent. Furthermore, below this interval self-supported films exhibit dependence of the dielectric constant on applied voltage and hysteretic behavior. This strongly suggests that below 90 K, the self-supported films undergo structural changes. The comparison of the lattice parameter at 300 K and 90 K, indicates that the substrate-supported films contract upon cooling with the thermal expansion coefficient close to that of the bulk values, whereas the self-supported films do not exhibit contraction at all. The most probable explanation of the observed effect is ordering of the oxygen vacancies due to the local lattice distortions we reported earlier (A. Kossoy and all, Adv.Func.Mat., 19, 4, 634, 2009).
9:00 PM - B5.26
Anode-Supported LSGMC Films for IT-SOFCs: Synthesis, Characterization and Processing.
Francesco Bozza 1 , Alessia Falsetti 1 , Oliver Schaef 2 , Philippe Knauth 2 , Enrico Traversa 1 3 , Riccardo Polini 1
1 , University of Rome Tor Vergata, Rome Italy, 2 , Université de Provence-CNRS, Marseille France, 3 , International Research Center for Materials Nanoarchitectonics, MANA-NIMS, Tsukuba Japan
Show AbstractPerovskites with composition La1-xSrxGa1-yMgyO3-δ, with δ=(x+y)/2, are among the most promising electrolyte materials for intermediate temperature SOFCs (IT-SOFCs). These electrolytes exhibit large ionic conductivities at 600–800 °C over a wide range of oxygen partial pressures. For x=0.2 and y=0.2, La0.8Sr0.2Ga0.8Mg0.2O2.8 shows an oxygen-ion conductivity of approximately 0.1 S/cm at 750 °C, comparable with that of YSZ at 1000 °C. Thus, LSGM-based SOFCs can be operated at 750 °C, or at even lower temperatures by using LSGM films. LSGM ion conductivity can be further increased by doping Co for gallium. La0.8Sr0.2Ga0.8Mg0.2−zCozO3−δ (LSGMC) powders containing different amounts of Co (z = 0.05 and 0.085) were prepared by a citrate sol–gel method. The powders were used to prepare both highly phase-pure LSGMC sintered pellets and, for the first time, anode-supported films using a simple and easily scalable technique such as Electrophoretic Deposition (EPD). LSGMC materials were subjected to X-ray photoelectron spectroscopy (XPS) characterization. XPS data confirmed the presence of the dopants in the material and allowed to identify two different chemical states for Sr2+ and oxygen, both related to the oxygen deficient perovskite structure of LSGMC. The conductivity of LSGMC sintered pellets containing different amounts of Co ions in the B sites of the perovskite lattice was assessed by electrochemical impedance spectroscopy (EIS) in the 250–750 °C temperature range. Conductivity values andapparent activation energies were in good agreement with previously published data referring to materials with same composition, but prepared by solid-state route. LSGMC powders (with z = 0.085) were deposited by electrophoretic deposition (EPD) onto a green membrane containing lanthanum-doped ceria (La0.4Ce0.6O2-x, LDC), a binder, and carbon powders. The LSGMC/LDC bilayer obtained by EPD was cofired at 1490 °C for 2 h. A dense and crack-free 8-µm-thick LSGMC film supported on a porous skeleton of LDC was obtained. The LDC porous skeleton was then infiltrated with Ni nitrate and calcined to obtain a cermet anode.The combined use of proper powder synthesis and film processing routes has thus proven to be a viable way for manufacturing anode-supported LSGMC films.
9:00 PM - B5.27
Reduction of the Fabrication-Induced Stress of YSZ-Membranes on Si.
Markus Piechotka 1 , Florian Kuhl 1 , Torsten Henning 1 , Benjamin Pachner 1 , Bruno Meyer 1 , Peter Klar 1
1 I. Physical Institute, JLU Giessen, Giessen Germany
Show AbstractYSZ is probably the best understood and most used solid electrolyte for high temperature solid oxide fuel cells (SOFC). Since sufficient current densities are only achieved at elevated temperatures above 500 °C, there is an urgent need for miniaturization of the fuel cell, so called µSOFCs, in order to optimize the currents. To achieve a lower resistivity and thus a higher current density at a constant temperature it is necessary to produce thinner YSZ membranes. These membranes are generally fabricated from YSZ thin films on Si substrates.A main issue of these membranes is to minimize the strain in the membrane due to the Si substrate. This strain leads to a bulging of the membranes due to stress relaxation. However, stress gradients along certain directions in-plane of the membrane may still exist depending on the membrane shape, i.e. diagonals of square-shaped membranes. Two approaches of minimizing the strain problem may be followed: the use of corrugated membranes instead of flat ones or alternatively an optimization of the membrane’s geometric shape.Membranes with higher symmetry yield lower stress near the membrane/thin-film borders and along high symmetry directions. Anisotropic etching of the Si substrate leads in general to a square geometry. Using specially designed masks for the etching process can provide geometries with higher symmetry, e.g. octagons from cross-shaped masks under the right etching conditions.In this work we will compare the shape of fabricated membranes with the simulated membrane geometry to confirm the considerations above. SEM, Raman and Laser microscope techniques are used to investigate the strain-induced curvatures of the membranes.
9:00 PM - B5.3
Control of Water Uptake for Polymer Electrolyte Membranes Based on Poly(phenylene) Derivatives.
Satoru Obayashi 1 , Masahiro Yoshizawa-Fujita 1 , Yuko Takeoka 1 , Masahiro Rikukawa 1
1 , Sophia University, Chiyoda-ku, Tokyo Japan
Show AbstractSulfonated aromatic polymers such as poly(p-phenylene)s have been widely investigated as polymer electrolyte membrane (PEM) materials for fuel cell applications due to their high thermal stability, high proton conductivity, and low in cost. However, sulfonated aromatic polymers have low mechanical properties under hydrous conditions. Swelling an excess amount of water causes the dimensional change of PEMs. Therefore, the control of water uptake for PEMs based on poly(phenylene) derivatives is one of critical demands for fuel cell applications. In order to control their water uptake, sulfonated poly(4-butylbenzoyl-1,4-phenylene)s (S-PBuBP) having alkyl groups on the phenyl group were synthesized. The sulfonated monomer, 2-butyl-5-(2,5-dichloro-benzoyl)-benzenesulfonic acid 2,2-dimethyl-propyl ester (NS-BuDBP), was polymerized via nickel-catalyzed coupling polymerization. The weight-average molecular weight of NS-PBuBP was determined by GPC measurement to be 102,000. S-PBuBP was synthesized by the deprotection of NS-PBuBP with diethylamine hydrobromide. The ion exchange capacity of S-PBuBP was 3.16 meq g-1. The sulfonation level calculated from the elemental analysis of S-PBuBP was consistent with the feed molar ratio of NS-BuDBP. The thermal stability of S-PBuBP was investigated by using TG-DTA. S-PBuBP showed no weight loss up to 210 °C, which was almost the same with those of other sulfonated poly(phenylene)s. The water absorption number of S-PBuBP increased with increasing relative humidity and was lower than that of sulfonated poly(4-phenoxybenzoyl-1,4-phenylene) (S-PPBP) (2.84 meq g-1) despite the higher IEC value. The water uptake of S-PBuBP was 30% under 90%RH at 80 °C. The percentage of freezable water in all the water absorption number was determined by DSC measurements to be about 15% under 100%RH, indicating that S-PBuBP had a high ratio of non-freezing water. It was suggested that the introduction of alkyl groups suppressed the adsorption of free water that was not intimately bound to the polymer. S-PBuBP in the dry state showed the tensile strength of 51.1 MPa and the ultimate elongation of 4%. In the hydrous state, the tensile strength was 21.4 MPa, which was higher than that of S-PPBP (Mw = 128,000). The proton conductivity of S-PBuBP increased with increasing relative humidity and was 1.73×10-1 S cm-1 under 90%RH at 80 °C.
9:00 PM - B5.4
Synthesis and Characterization of TMPd-Au (TM= Ni, Co, Cu) Nanoparticles for Electrocatalytic Applications.
Sally Ho 1 , Shouheng Sun 1
1 Chemistry, Brown University, Providence, Rhode Island, United States
Show AbstractWith high conversion efficiencies and benign byproducts, fuel cells have emerged as alternative power sources. Mainstream commercialization is hindered by the scarcity and high cost of the nanocatalysts; as such, research has been directed towards the development of catalysts limiting precious metal usage with a focus on increasing activity and durability through the incorporation of other elements. We report our progress on surfactant-mediated synthesis of transition-metal palladium based alloy nanoparticles with composition and size control. These nanoparticles were subsequently used as seeds for the selective nucleation of growth and nucleation of gold, resulting in the formation of dumbbell shaped nanoparticles. Preliminary results show increased specific activity of the dumbbell nanoparticles compared to their single metal counterparts for the formic acid oxidation. This study shows the activity of nanoparticles can be enhanced through via a multimetallic catalyst.
9:00 PM - B5.5
Improvement of Activity for Oxygen Reduction Reaction by Strong Metal-Metal Oxide Interaction in the Precious Metal Supported on Metal Oxide-Carbon Composite Supports.
Seon-ah Jin 1 , Dae Jong You 1 , Kang Hee Lee 1 , Chanho Pak 1
1 Energy Lab, Samsung Advanced Insitute of Technology, Yongin, Gyunghi0do, Korea (the Republic of)
Show AbstractThe polymer electrolyte membrane fuel cells (PEMFCs) have been regarded as a next systems that have a lot of potential applications in transportation, power generation, and portable electronic devices, due to their high energy-conversion efficiency, low temperature of operation, and environmental benefits. PEMFC are about to commercialize for the residential and portable power applications according to the decent efforts from the academia, governments and industry. However, there are still challenges about the durability and cost of the fuel cells for expanding the market size. Recently, catalyst nanoparticles having core-shell structure based on Pt and non-Pt elements has been explored to overcome the above issues for the PEMFC. Adzic and coworkers reported the precious metal core-Pt shell catalyst had a higher oxygen reduction reaction activity and stability than Pt catalyst [1]. In addition, Pd-based catalyst showed an improved oxygen reduction reaction (ORR) activity using intermetallic compound formed via heat treatment of Pd on the metal oxide-carbon composite support [2]. In this study, the effect of interaction between metal oxide core and metal shell on the ORR activity was investigated using sequential impregnation of metal precursor on the preformed metal oxide-carbon composite support and high temperature reduction process. The activity for ORR by these catalysts was enhanced, which attributed to the strong metal-metal oxide interaction. [1] K. Sasaki, J.X. Wang, N. Marinkovic, K. More, H. Inadan and R.R. Adzic, Electrochim. Acta 55 (2010) 2645-2652.[2] S.-A. Jin, K. Kwon, C. Pak and H. Chang, Catal. Today 164 (2011) 176-180.
9:00 PM - B5.6
Dioxygen Reduction Study of Doped Carbon Nanowalls Deposited on the Surface of Glassy Carbon Electrodes.
Joshua McClure 1 2 , Jackson Thornton 3 , Rongzhong Jiang 2 , Deryn Chu 2 , Jerrome Cuomo 3 , Peter Fedkiw 1
1 Chemical and Biomolecular Engineering, NC State University, Raleigh, North Carolina, United States, 2 Sensors and Electron Devices Directorate, Army Research Lab, Adelphi, Maryland, United States, 3 Materials Science and Engineering, North Carolina State University, Raleigh, North Carolina, United States
Show AbstractAnion exchange membrane fuel cells (AEMFCs) use OH- conducting polymer electrolytes to separate the anode from the cathode. AEMFCs use expensive platinum and platinum-group metals (PGMs) for anode and cathode electrocatalysts. However, the use of OH- conducting polymer materials creates a high pH environment that is less corrosive than traditional acidic proton exchange membrane fuel cells (PEMFCs), thus possibly allowing less expensive non-PGM electrocatalysts for the oxygen reduction reaction (ORR). Nitrogen-doped graphene-like materials have been given attention as a potential non-PGM electrocatalyst. Furthermore, nitrogen-doped graphene-like materials have been reported to reduce O2 more efficiently to OH- in basic media than non-doped carbon materials, and may potentially replace transition-metal electrocatalysts or electrocatalyst supports. In this study, a radio frequency (RF) N2 plasma post-processing treatment is used to grow and subsequently dope nitrogen and oxygen into plasma-enhanced chemical vapor deposited (PECVD) carbon nanowalls (CNWs). CNWs are directly grown on glassy carbon (GC) disk electrodes in a fabricated quartz-disk holder, and the electrochemical properties are studied using rotating ring disk electrode (RRDE). The CNWs show kinked walls perpendicular to the GC disk as observed by scanning electron microscopy (SEM), and the CNW-covered GC disks are placed into a Teflon-shrouded electrode using a specially-designed assembly block. This process allows for high-throughput screening of PECVD grown graphene-like materials. The materials are subsequently doped using nitrogen and oxygen and a RRDE study of the dioxygen reduction properties yields results pertaining to the mass and specific activities as a function of doping concentration and other processing conditions. X-ray photoelectron spectroscopy (XPS) is used to probe the surface functional groups present before and after nitrogen doping. After plasma treatment, nitrogen and oxygen are shown to be present with a broad atomic percent incorporation. It is found that precursor materials with higher starting oxygen content lead to an increase in nitrogen incorporation. All samples are compared using Micro-Raman spectroscopy to provide ID/IG and fwhm information for the bonding character of the carbon materials before and after nitrogen doping. Finally, select nitrogen-doped materials that exhibit superior properties compared to non-doped materials are made in bulk amounts, and various metals including Pd and Ag are added to the surface of these doped graphene-like materials using different deposition methods. Select carbon materials are evaluated with FE-TEM and energy dispersive spectroscopy (EDS).
9:00 PM - B5.7
Composite Membranes Based on SPEEK and Functionalized Titania for Polymer Electrolyte Membrane Fuel Cell.
Maria Luisa Di Vona 1 , Emanuela Sgreccia 1 , Philippe Knauth 2 , Gerhard Auer 3
1 , Dip. Scienze e Tecnologie Chimiche, University of Rome Tor Vergata, Rome Italy, 2 , Université de Provence, Marseille France, 3 , Crenox Pigments GmbH, Krefeld Germany
Show AbstractPolyaromatic polymers, such as polyetherketones (PEEK), show a chemical, mechanical and thermal stability like that of fluorinated polymers, but at low cost. Another interesting aspect of polyaromatic polymers is the possibility of functionalization reactions, such as sulfonation. SPEEK shows rather large conductivity when sulfonated, but its mechanical, solubility and morphological properties progressively deteriorate with the degree of sulfonation (DS), because acid groups directly linked to the aromatic hydrophobic backbones cannot assemble in phase separated domains. The introduction of an inorganic filler into the ionic conductor may stabilize the polymeric phase, overcome the temperature barrier limit, reduce fuel crossover, and improve the mechanical strength of the material without sacrificing important polymer properties necessary to operate in FCs. We have studied composites of SPEEK with surface-functionalized TiO2, one with hydrophilic (trihydroxy-propane) and one with hydrophobic molecules (silicon oil). Composites with hydrophilic TiO2 show large agglomeration of oxide particles and an inhomogeneous microstructure, but the agglomeration of titania particles together with segregation of sulfonic acid groups gives high proton conductivity. The composites with hydrophobic TiO2 present a very homogeneous microstructure with well dispersed oxide nanoparticles. However, this composite presents relatively low proton conductivity. It is clear that further fine-tuning of the surface treatment is worthwhile to get an optimal compromise between high conductivity and homogeneous microstructure.References1. M. L. Di Vona, E. Sgreccia, S. Licoccia, M. Khadhraoui, R. Denoyel and P. Knauth, Chem. Mater. 20, 4327 (2008).2. M. L. Di Vona, E. Sgreccia, A. Donnadio, M. Casciola, J. F. Chailan, G. Auer and P. Knauth, J. Membr. Sci. (2011), 369, 536–544 (2011).3. G. Auer, E. Sgreccia, M. L. Di Vona, Brennstoffzellmembran, Patent Application DE 10 2009 006493 A1.
9:00 PM - B5.8
Proton-Conducting Polymers: Relations between Macromolecular Structure, Water Activity and Proton Mobility.
Philippe Knauth 1 , M. Luisa Di Vona 2
1 LCP-MADIREL, University of Provence-CNRS, Marseille France, 2 Dip. Scienze Tecnologie Chimiche , University of Roma Tor Vergata, Roma Italy
Show AbstractSulfonated Aromatic Polymers (SAPs) are credible alternative polymer electrolytes for Proton Exchange Membrane Fuel Cells. Objective of the development is to obtain a suitable proton-conducting polymer for use at intermediate temperatures (typically 120°C) and under low relative humidity and to improve long-term durability.In our recent work, we focus on the study of physico-chemical properties of various SAP, including Sulfonated Poly-Ether-Ether-Ketone (SPEEK) with various Degree of Sulfonation, but also Sulfonated PolyPhenylSulfone (SPPSU) and cross-linked derivatives, obtained by innovative synthesis procedures or by optimized thermal annealing. [1-4]In this presentation, we will discuss the water activity and proton mobility in the acid solutions present inside the polymer matrix. [5] These data are obtained from water uptake isotherms and proton conductivity measurements by impedance spectroscopy. The presence of the polymer matrix is observed in several aspects.The effect on water activity can be taken into account by the visco-elastic properties of the polymer, introducing their yield stress. The water activity of various SAP and Nafion tends to be very similar at intermediate humidification levels. The effect on proton mobility can be discussed taking into account the tortuosity of the membranes and the percolation threshold of the nanometric aqueous channels inside the matrix. 1. E. Sgreccia et al., J. Power Sources, 192, 353-359 (2009).2. M. L. Di Vona et al. J. Phys. Chem. B, 113, 7505–7512 (2009).3. M.L. Di Vona et al., J. Membrane Sci., 354, 134-141 (2010).4. E. Sgreccia, M. L. Di Vona, P. Knauth, Int. J. Hydrogen Energy, 36, 8063-8069 (2011).4. P. Knauth et al., J. Electrochem. Soc., 158, B159-165 (2011).
9:00 PM - B5.9
Improvement of Electrochemical Activity of Pt/MWCNT Catalyst for Proton Exchange Membrane Fuel Cell.
Battsengel Baatar 1 , Bayardulam Jamiyansuren 1 , Munkhshur Myakhlai 1 , Baasandorj Myagmarsuren 1
1 Chem Tech, NUM, Ulaanbaatar Mongolia
Show AbstractIn last years the carbon nanotubes have been studied as an advanced metal catalyst support for proton exchange membrane fuel cell. This study focuses on the sonochemical treatment of multi walled carbon nanotubes (MWCNTs) as a platinum supporting material for proton exchange membrane fuel cell (PEMFC) by mixture of sulfuric acid and nitric acid and also mixture of sulfuric acid and hydrogen peroxide. X-ray diffraction (XRD) and Infrared (IR) spectroscopy were used to characterize the surface of sonochemically treated MWCNT and nanostructured electrocatalyst Pt/MWCNT. According to the experimental results of this work, the surface of MWCNT can be more successfully functionalized with hydroxyl and carboxyl groups after sonochemical treatment by mixture of sulfuric acid and nitric acid. The particle size of prepared Pt –electrocatalyst on MWCNT was determined 3.4 nm by XRD. Electrochemical activity of electrocatalyst was studied by cyclic voltammetry.
Symposium Organizers
Maria Luisa Di Vona University of Rome Tor Vergata
Joshua Hertz University of Delaware
Philippe Knauth University of Provence
Harry L. Tuller Massachusetts Institute of Technology
B6: PEM Theory
Session Chairs
Tuesday AM, November 29, 2011
Constitution B (Sheraton)
10:00 AM - **B6.1
The Effects of Nanoscale Confinement on Proton Mobility in Model Perfluorosulfonic Acid Systems.
Bradley Habenicht 1 , Stephen Paddison 1
1 Chemical & Biomolecular Engineering, University of Tennessee, Knoxville, Tennessee, United States
Show AbstractProton exchange membrane (PEM) fuel cells still utilize perfluorosulfonic acid (PFSA) ionomers as the electrolyte. Upon hydration these solid polymers exhibit a nanophase-separated morphology with the water confined to domains of only a few nanometers. Significant effort continues in the development of PEMs that possess high proton conductivity (> 0.10 S/cm) under low humidity conditions. The characteristic dimensions of the phase-separated morphology of hydrated PFSA ionomers along with the acidity, density, and distribution of the sulfonic acid groups determines the transport of both water and protons.In an effort to understand the effects of confinement on proton transfer in PFSA ionomers at minimal hydration carbon nanotubes (CNTs) were functionalized with –CF2SO3H groups and hydrated with 1 to 3 water molecules per sulfonic acid. The distance between sulfonate groups was systematically varied from 6 to 8 Å and three different CNTs were used to determine the effects of nanoscale confinement. The inner walls of the CNT were either functionalized with fluorine atoms to a provided localized negative charge or left bare to provide a more delocalized charge distribution. It was shown that decreasing the distance between sulfonate groups increased proton dissociation, as well as the interactions between water molecules. As the sulfonate distance increased, connectivity amongst the water molecules decreased as they formed more isolated clusters around the sulfonate groups. The sulfonate distance and geometry was the most dominant factor in proton dissociation, however, the hydrophobic environment and nanoscale confinement became more important as the distance between sulfonate groups increased. Implications of the results from these ideal systems on low equivalent weight PFSA membranes will be discussed.
10:30 AM - B6.2
Lattice Boltzmann Simulation of Multiphase Transport in Nanostructured Cathode Catalyst Layer for Proton Exchange Membrane Fuel Cells.
Christopher Stiles 1 , John Elter 1 , Yongqiang Xue 1
1 College of Nanoscale Science and Engineering, SUNY Albany, Albany, New York, United States
Show AbstractWe present a 2D mesoscopic model of multiphase transport in an ordered nanostructured cathode catalyst layer (CCL) for proton exchange membrane fuel cells (PEMFC) applying the Lattice Boltzman equation (LBE). In the ordered nanostructured CCL, nanotubes/nanowires are used as support materials for Pt catalyst, upon which a thin layer of proton-conducting polyer is deposited, which are then aligned along the main transport direction of the various species. Diffusive wall boundary conditions are established to account for the catalytic reactions in the multicompoent mixtures within the CCL based on an accurate interpolation scheme. Results from the LBE model of the reactive microflow are then compared with a finite-element Navier-Stokes solver in terms of the effects on the performance of the nanostructured CCL due to varying nanotube/nanowire length, spacing and surface wettability.
10:45 AM - B6.3
First Principle Transition State Study of Oxygen Reduction Reaction on Pt (111) Surface Modified by Subsurface Transition Metals.
Zhiyao Duan 1 , Guofeng Wang 1
1 Department of Mechanical Engineering and Materials Science, University of Pittsburgh, Pittsburgh, Pennsylvania, United States
Show AbstractTo improve the efficiency and simultaneously reduce the production cost of proton exchange membrane fuel cells (PEMFC), much research effort has been devoted to alloying Pt cathode with other transition metals to find novel electrocatalysts of PEMFC. In particular, surface segregation process (in which precious Pt enriches the outermost layer and transition metals enrich the subsurface layer of the catalyst surface) was found useful in enhancing the activity of the Pt alloy electrocatalysts. In this study, we have performed first-principle density functional theory calculations to investigate how subsurface transition metal M (M = Ni, Co, or Fe) affects the energetics and mechanisms of oxygen reduction reaction (ORR) on the outermost Pt mono-surface layer of Pt/M (111) surfaces. In this work, we found that the subsurface Ni, Co, and Fe could down-shift the d-band center of the Pt surface layer and thus weaken the binding of chemical species to the Pt/M (111) surface. Moreover, the subsurface Ni, Co, and Fe could modify the heat of reaction and activation energy of various elementary reactions of ORR on these Pt/M (111) surfaces. Our DFT results revealed that due to the influence of the subsurface Ni, Co, and Fe ORR would adopt hydrogen peroxide dissociation mechanism with an activation energy of 0.15 eV on Pt/Ni (111), 0.17 eV on Pt/Co (111), and 0.16 eV on Pt/Fe (111) surface, respectively, for their rate-determining O2 protonation reaction. In contrast, ORR would follow peroxyl dissociation mechanism on pure Pt (111) surface with activation energy of 0.79 eV for its rate-determining O protonation reaction. Thus, our theoretical study explained from a reaction kinetics point of view that the subsurface Ni, Co, and Fe could lead to multi-fold enhancement in catalytic activity for ORR on the Pt mono-surface layer of Pt/M (111) surfaces.
11:00 AM - B6: PEM theory
BREAK
B7: PEM Electrodes I
Session Chairs
Tuesday PM, November 29, 2011
Constitution B (Sheraton)
11:30 AM - B7.1
Characterization of High-Surface-Area PtRu/Carbon Direct Methanol Fuel Cell Catalysts Functionalized via Nitrogen Implantation.
Ryan O'Hayre 1 , Svitlana Pylypenko 1 , Kevin Wood 1 , Arrelaine Dameron 2 , Tim Olson 2 , Kevin O'Neill 2 , Steven Christensen 2 , David Ginley 2 , Thomas Gennett 2 , Tim Holme 4 , Karren More 3 , Albina Borisevich 3 , Huyen Dinh 2
1 Metallurgical and Materials Engineering, Colorado School of Mines, Golden, Colorado, United States, 2 , National Renewable Energy Laboratory, Golden, Colorado, United States, 4 Materials Science and Engineering, Stanford University, Stanford, California, United States, 3 , Oak Ridge National Laboratory, Oak Ridge, Tennessee, United States
Show AbstractThe activity and durability of fuel cell catalyst materials can be significantly influenced by catalyst-support interactions. Functionalization of carbon supports with nitrogen has been shown to enhance catalyst-support interactions, and therefore affect catalyst performance and utilization. Initial insight into the role of the nitrogen on the catalyst dispersion, stability and catalytic activity will be presented using model nitrogen-implanted highly-oriented pyrolitic graphite (HOPG)/catalyst systems combined with Density Functional Theory (DFT) calculations to further our understanding of the possible effect of the nitrogen functionalities and aid in the design of the N-doped high-surface area functional support. We will then discuss the level of nitrogen doping that can be achieved on commercially-relevant high surface area materials, such as Vulcan and Graphitic Vulcan, and detail chemical and morphological changes associated with the implantation. We will show that ion implantation leads to formation of various functional nitrogen groups, such as pyridinic, pyrrolic and graphitic nitrogen and discuss their potential effect on catalyst performance. Analysis of the catalyst surface morphology with high resolution transmission electron microscopy (TEM) demonstrates that nitrogen doping affects nucleation of the Pt catalyst nanoparticle phase. Further, we disclose Electron energy loss spectroscopy (EELS) imaging data demonstrating, for the first time, remarkable correlation between the location of Pt catalyst nanoparticles and nitrogen sites.
11:45 AM - B7.2
Low-Temperature Seeding-Assisted Synthesis of Monodispersed Hyperbranched PtRu Nanoparticles and Their Electrocatalytic Activity in Methanol Oxidation.
Yujing Li 1 , Yu Huang 1 2
1 Materials Science and Engineering, University of California, Los Angeles, Los Angeles, California, United States, 2 California NanoSystems Institute, University of California, Los Angeles, Los Angeles, California, United States
Show AbstractPt-Ru nanoparticles (NPs) are attracting major interests as anode electrocatalysts for methanol oxidation. Different synthetic approaches have been developed to obtain PtRu NPs with different sizes and compositions. In our work, we report a new approach to synthesize PtRu NPs with hyperbranched (HB) morphology by a Pt seeding-assisted growth mechanism at room temperature. As-synthesized PtRu NPs can be well dispersed in aqueous solution. The ratio of the Ru/Pt can be controlled between 1/5 to 1 by manipulating the injection of Ru precursor (RuCl3). By exploring the growth mechanism, it has been found that the reduction of Ru undergoes a Ru2+ intermediate and further to zero valence. The investigation of electro-oxidation of methanol indicates that the HB PtRu NPs enhance the oxidation current density by 3 folds compared with PtRu NPs with irregular shapes and 2 times that of commercial PtRu black. We proposed that the enhancement can be partly assigned to the existence of high-index facets exposed on the particle surface, confirmed by high resolution transmission electron microscopy, and partly assigned to the structure factor of the HB morphology based on the commonly accepted bifunctional mechanism of methanol oxidation, because the methanol molecule and oxygen atom, adsorbed on different branches have the chance to react due to the small steric spacing between branches.
12:00 PM - B7.3
Composite Layer-by-Layer/Electrospun Polymer Electrolyte Membranes for Use in Direct Methanol Fuel Cells.
Matthew Mannarino 1 , David Liu 2 , Paula Hammond 2 , Gregory Rutledge 2
1 Department of Materials Science & Engineering, Massachusetts Institute of Technology, Cambridge, Massachusetts, United States, 2 Department of Chemical Engineering, Massachusetts Institute of Technology, Cambridge, Massachusetts, United States
Show AbstractThe advancement of electrochemical energy devices such as direct methanol fuel cells (DMFCs) is critically dependent on the improved performance of thin solid polymer electrolytes used in the proton exchange membrane (PEM). The essential properties for the polyelectrolyte PEM used in DMFCs include high ionic conductivity, low fuel/charge crossover, and mechanical stability. PEM fabrication by electrostatic layer-by-layer (LBL) assembly of sulfonated poly(2,6-dimethyl-1,4-phenylene oxide) and poly(diallyl dimethyl ammonium chloride) [sPPO/PDAC] has been shown to provide ionic conductivity comparable to that of the industry standard, Nafion®, while achieving a two order of magnitude reduction in methanol crossover; however, LBL-assembled PEMs suffer from poor mechanical integrity when fully hydrated. Improvements in the mechanical performance of these multilayer assembled PEMs can be achieved by integrating the PEM within a mechanically robust, porous nanofiber matrix. Electrospinning can be used to create these porous nanoscale polymer fiber scaffolds to provide mechanical support as well as mimic the percolated, fibrillar structure of water-swollen Nafion®. The combination of the two processes to create a composite LBL/nanofiber membrane allows for decoupling of the structure and mechanical properties of the membrane from the chemical and transport properties; thus, the nanofiber mat and LBL deposition can each be tailored independently of each other and then combined to create the optimal composite PEM. Poly(trimethyl hexamethylene diamine terephthalamide) [PA 6(3)T], was used as the electrospun nanofiber “endo-skeleton” for the PEM due to its high strength, tunable fiber diameter and relative ease of fabrication. The mechanical properties of the PA 6(3)T mats can be tailored post-spinning by heat treatment without significantly affecting the porosity. The robustness of the nanostructured composite membranes were found to be drastically improved over the freestanding LBL films without significantly affecting the transport properties. These novel composite PEMs have been tested in a DMFC and preliminary results have shown higher OCV (compared to Nafion®) as expected from reduced methanol permeability and the potential for improved fuel cell output with further optimization.
12:15 PM - B7.4
Conductive Tungsten Oxide Nanowires-Supported Pt Nanodendrites as Efficient Electrocatalysts for Methanol Oxidation.
Youngjin Ye 1 , Jin Joo 2 , Byungkwon Lim 3 , Jinwoo Lee 1
1 Department of Chemical Engineering, Pohang University of Science and Technology (POSTECH), Pohang Korea (the Republic of), 2 Department of Applied Chemistry, Kyungpook National University, Daegu Korea (the Republic of), 3 School of Advanced Materials Science and Engineering, Sungkyunkwan University, Suwon Korea (the Republic of)
Show Abstract Platinum (Pt) nanoparticles are the most effective electrocatalysts for reactions involving small organic molecules such as methanol and ethanol. Their catalytic activity highly depends upon their morphology. Design of Pt nanostructures, therefore, has a significant importance to enhance their catalytic activity. Among the various nanostructures, Pt nanodendrites have attracted great interest for use as electrocatalysts in fuel cell applications, since their relative large surface area and interconnected structures intrinsic to the dendritic morphology lead to the enhanced catalytic activity toward specific reactions such as oxygen reduction and methanol oxidation. Pt nanoparticles supported on tungsten oxide are known to be efficient catalysts in methanol oxidation for the following reasons. First, tungsten oxide is known to form a hydrogen bronze that facilitates dehydrogenation during methanol oxidation. Second, the CO intermediates, which act as poison on the catalyts for the methanol oxidation, can be oxidized by the hydroxyl groups on the surface of tungsten oxide. In spite of these advantages, enhancement of catalytic activity with Pt supported on tungsten oxide is limited due to the poor electrical conductivity of typical tungsten oxide (WO3). In this work, we report the simple colloidal synthesis of Pt nanodendrites supported on conductive tungsten oxide (W18O49) nanowires as efficient electrocatalysts for methnol oxidation reaction. Tungten oxide nanowires grown along the [010] direction have critical role in growth of dendritic structures of Pt. We found that the synthesized nanoparticles exhibit 1.4 times higher mass activity and 9.3 times higher specific activity for methanol oxidation than those of Pt/C commercial catalyst. High CO tolerance and durability were confirmed by the CO stripping and chronoamperometry experiments. Our simple and viable method can be extended to the synthesis of morphology-controlled Pt nanostructures supported on various metal oxides as efficient and durable anode electrocatalysts for direct methanol fuel cells.
12:30 PM - B7.5
A General Protocol for Synthesizing Pt-Sn/C Catalysts via the Polyol Method for Ethanol Electrooxidation.
Jim Lee 1 , Bo Liu 1 , Zhi-Wen Chia 1 , Zhen-You Lee 1
1 Chemical & Biomolecular Engineering, National University of Singapore, Singapore Singapore
Show AbstractThe direct ethanol fuel cells (DEFCs) have the salient advantage of using a high-energy density (~ 8 kWh/kg) liquid fuel of low toxicity that can be produced renewably (i.e. “bioethanol”). The major technical challenge of DEFCs is the slow kinetics of the ethanol oxidation reaction (EOR) at the anode. Pt-Sn/C catalysts are currently the most active anode catalysts for ethanol electrooxidation at low potentials. Pt-Sn/C catalysts can be prepared by many methods. Among them the polyol method where ethylene glycol is used as a solvent, a reducing agent and a capping agent (via its partially oxidized products), is the most effective for depositing small catalytic metal nanoparticles (~3 nm) on the carbon catalyst support. However, there are significant differences in the published details of the preparation of Pt-Sn catalysts by the polyol method such as the synthesis conditions, and catalyst composition and catalyst performance for ethanol electrooxidation. A systematic investigation of the effects of synthesis parameters can therefore contribute to improving the preparation and performance of the Pt-Sn/C catalysts for ethanol oxidation.We have carried out a fairly comprehensive determination of the effects of the synthesis parameters. We found the percentage of Sn on the surface was often higher than in the bulk, indicating surface enrichment effects driven by the greater affinity of Sn for oxygen than for Pt. We also found that adequate HCl acidification (to pH<2) after the synthesis was necessary for the complete transfer of the Pt-Sn colloids formed to the carbon support. 100% utilization of the Sn precursor was possible if water was present as a co-solvent in the polyol synthesis with careful control of the ethylene glycol to water ratio (1:1 was optimal). The addition of NaOH solution to the synthesis solution for pH adjustment before ethylene glycol reduction was the key to forming sufficiently small metal nanoparticles. We also found that a Pt:Sn ratio of 3:1 was best for ethanol electrooxidation.
12:45 PM - B7.6
Highly Active Iridium/Iridium–Tin/Tin Oxide Heterogeneous Nanoparticles as Alternative Electrocatalysts for the Ethanol Oxidation Reaction.
Xiaowei Teng 1
1 Chemcial Engineering, University of New Hampshire, Durham, New Hampshire, United States
Show AbstractEthanol is becoming a promising fuel for low–temperature direct fuel cell reactions. However, the implementation of ethanol fuel cell technology has been hindered by the lack of low-cost, highly active anode catalysts. Here we have studied Iridium (Ir) based binary catalysts as low-cost alternative electrocatalysts replacing platinum (Pt)-based catalysts for the direct ethanol fuel cell (DEFC) reaction. We report the synthesis of carbon supported Ir-Sn catalysts with an average diameter of 2.7 ± 0.6 nm through a “surfactant–free” wet chemistry approach. The complementary characterization techniques, including aberration–corrected scanning transmission electron microscopy (STEM) equipped with electron energy loss spectroscopy (EELS), X–ray diffraction (XRD), X–ray photoelectron spectroscopy (XPS), and X–ray absorption spectroscopy (XAS), are used to identify the “real” heterogeneous structure as of Ir/Ir-Sn/SnO2, which consist of an Ir-rich core, and an Ir-Sn alloy shell with SnO2 present on the surface. The Ir-Sn/C heterogeneous catalyst exhibited high electrochemical activity towards the ethanol oxidation reaction compared to the commercial Pt/C (ETEK), PtRu/C (Johnson Matthey) as well as PtSn/C catalysts. Electrochemical measurements and density functional theory (DFT) calculations demonstrate that the superior electro-activity is directly related to the high degree of Ir-Sn alloy formation, as well as the existence of non-alloyed SnO2 on surface. Our cross–disciplinary work, from novel “surfactant–free” synthesis of Ir–Sn catalysts, theoretical simulations, catalytic measurements, to the characterizations of “real” heterogeneous nanostructures, will not only highlight the intriguing structure-property correlations in nanosized catalysts, but also have a transformative impact on the commercialization of DEFC technology by replacing Pt with low cost, highly active Ir-based catalysts.
B8/C5: Joint Session: SOFC Materials Characterization I
Session Chairs
Juergen Fleig
Harry Tuller
Tuesday PM, November 29, 2011
Constitution B (Sheraton)
2:30 PM - **B8.1/C5.1
FIB/SEM Reconstruction and 3D Simulations of SOFC Electrodes.
Ellen Ivers-Tiffee 1 3 , Jochen Joos 1 , Thomas Carraro 2 , Moses Ender 1
1 Institut für Werkstoffe der Elektrotechnik (IWE), Karlsruher Institut für Technologie (KIT), Karlsruhe Germany, 3 DFG Center for Functional Nanostructures (CFN), Karlsruher Institut für Technologie (KIT), Karlsruhe Germany, 2 Institut für Angewandte Mathematik (IAM), Universität Heidelberg, Heidelberg Germany
Show AbstractThe microstructures of high performance La0.58Sr0.4Co0.2Fe0.8O3-δ (LSCF) and Ni/8YSZ electrodes are reconstructed using a dual-beam focused ion beam / scanning electron microscopy (FIB/SEM) system. This method has already proven potential for the detailed analysis of microstructures [1-2]. The corrected reconstruction data are the basis for the calculation of the microstructure parameters (i) volume-specific surface area of the individual phases (ii) volume/porosity fractions, (iii) tortuosity and in case of composite electrodes (iv) triple phase boundary density. These parameters constitute the basis to calculate electrode performance via simplified microstructure models and the accurate determination of these parameters will be shown. However, it would be desirable to fit the reconstructed microstructure directly into a more accurate 3D-model. Therefore a 3D finite element method model was developed, which enables a direct use of the corrected 3D FIB/SEM data. The model is able to calculate (among other things) the spatial distribution of oxygen concentration and the area specific resistance of the electrode. First results of this model, including a parameter sensitivity analysis, are presented.[1] J. R. Wilson, W. Kobsiriphat, R. Mendoza, H. Y. Chen, J. M. Hiller, D. J. Miller, K. Thornton, P. W. Voorhees, S. B. Adler, and S. A. Barnett, nature materials, 5 (7), p. 541 (2006).[2] J. Joos, T. Carraro, A. Weber, and E. Ivers-Tiffée, J. Power Sources, 196, (17), p. 7302 (2010).
3:00 PM - B8.2/C5.2
Imaging Analysis of Aggregation Behavior in Reduced NiO-YSZ.
Laxmikant Saraf 1 , David King 1 , Chongmin Wang 1 , A. Lea 1 , Zihua Zhu 1 , James Strohm 1 , Donald Baer 1
1 , Pacific Northwest National Laboratory, Richland, Washington, United States
Show AbstractExploring overlooked properties of traditional materials used for solid oxide fuel cell (SOFC) is as important as the development of new materials to improve its ion transport at the intermediate temperature range. NiO-YSZ has been extensively studied as a SOFC anode due to high catalytic activity and affordability NiO to steam reform hydrocarbons for hydrogen generation in anode supported and direct hydrocarbon fuel feed SOFCs. In this study, we explore high resolution imaging analysis of reduced NiO-YSZ to establish its direct correlation with energy dispersive X-ray spectroscopy (EDS) chemical mapping. The correlation among NiKα maps with scanning transmission electron microscopy (STEM) indicate Ni/NiO aggregation behavior in extensively reduced NiO-YSZ. Widely known reduction reaction of NiO into Ni and stability of YSZ in reducing conditions can also be visualized by correlating ZrKα, NiKα and OKα maps. The nickel mobility on the widely varying bulk and intra-particle length scales is discussed in the context of reducing conditions. The aggregation behavior of Ni/NiO in NiO-YSZ is compared with growth and aggregation of pure fluorite structure materials frequently used in SOFCs to discuss the impact of reducing conditions and temperature on grain growth and transport properties.
3:15 PM - **B8.3/C5.3
Microstructural and Electrochemical Studies of Solid Oxide Fuel Cell Durability.
Scott Barnett 1
1 Materials Science, Northwestern Univ, Evanston, Illinois, United States
Show AbstractThis talk will describe accelerated testing of solid oxide fuel cell (SOFC) durability combining 2D and 3D imaging with detailed electrochemical characterization. The aim of accelerated testing is to predict performance over ~40,000 h lifetimes, but meaningful extrapolation of the data requires accurate mechanistic models of degradation mechanisms; quantitative imaging is an aid to developing such models. A few examples of degradation studies will be discussed. First, degradation of cathodes consisting of Gd-doped Ceria infiltrated with (La,Sr)(Fe,Co)O3 is described, and a model based on coarsening of LSCF nano-particles is used to explain the data. Second, 3D FIB-SEM studies are presented showing structural and electrochemical changes in Ni-YSZ anode active layers upon extended annealing, including a surprising effect where pores become increasingly isolated. Third, structural and electrochemical changes in LSM-YSZ electrodes during cyclic operation, between fuel cell cathode mode and electrolyzer anode mode, will be discussed.
3:45 PM - B8.4/C5.4
Correlating Nanostructure and Ion Conductivity in Gadolinium and Praseodymium Doped and Co-Doped Cerias for Solid Oxide Fuel Cell Electrolytes.
William Bowman 1 2 , Albert Talin 2 , Renu Sharma 2 , Vaneet Sharma 1 , Peter Crozier 1
1 School for Engineering of Matter, Transport and Energy, Arizona State University, Tempe, Arizona, United States, 2 Center for Nanoscale Science and Technology, National Institute of Standards and Technology, Gaithersburg, Maryland, United States
Show AbstractRare-earth doped ceria (CeO2) is a potential candidate material for intermediate temperature (500 °C to 700 °C) solid-oxide-fuel-cell (IT-SOFC) electrolytes. Ceria doped with aliovalent dopants has been found to possess high oxygen-ion conductivity in this temperature range. Understanding the relationship between nanostructure and ionic conductivity is essential to provide fundamental knowledge of the atomic-level migration mechanisms of oxygen ions in these electrolyte materials to allow for their optimization. Here we investigate the variation in ion conductivity with dopant concentration for a series of Pr-doped, Gd-doped and Pr/Gd-co-doped materials synthesized using a spray-drying technique. Ionic conductivity measurements are made using impedance spectroscopy and will be presented for these samples as well as pure ceria specimens. Grain size distribution and composition is expected to affect the results and we present data on these parameters for our samples, determined using scanning electron microscopy (SEM) with energy dispersive x-ray spectroscopy (EDX). Similarly, the segregation of dopant atoms to grain boundaries is thought to have a significant effect on oxide ion transport through doped ceria. We discuss the correlations between the nanostructure compositional heterogeneity – measured using high spatial resolution electron energy-loss spectroscopy in a scanning transmission electron microscope – and ionic conductivity. We compare our results with those generated by Dholabhai et al [1,2], who have used density functional theory (DFT) and a kinetic-lattice Monte Carlo (KLMC) model to investigate the variation in ion conductivity with dopant concentrations for single crystal binary and tertiary oxides.References:[1] P. P. Dholabhai, J. B. Adams, P. Crozier, R. Sharma, "Oxygen vacancy migration in ceria and Pr-doped ceria: A DFT+U study," The Journal of Chemical Physics, vol. 132, Mar. 2010. [2]P. P. Dholabhai, J. B. Adams, P. Crozier, R. Sharma, "A density functional study of defect migration in gadolinium doped ceria," Physical Chemistry Chemical Physics, no. 12, May 2010; pp. 7904-7910.
4:30 PM - **B8.5/C5.5
Compositional Studies of SOFC Cathode Surfaces by Low Energy Ion Scattering (LEIS).
John Kilner 1 2 , Monica Burriel 1
1 Materials, Imperial College,London, London United Kingdom, 2 I2CNER, Kyushu University, Kyushu Japan
Show AbstractOne of the major obstacles to the optimization of electrodes for high temperature electrochemical devices, such as the cathode for the SOFC or the anode for the SOEC, is the current rudimentary understanding of the oxygen surface exchange process. Despite decades of isotopic, electrochemical and theoretical studies we still have a rather poor understanding of the way that the oxygen in the gas phase interacts with the surface of an oxide. Part of the problem is that we do not understand how the outer surface composition and surface structure relate to the bulk composition, and other factors such as the presence of impurities, under the operating conditions relevant to the SOFC (or SOEC). It has thus become imperative that we investigate the surface composition of these materials so that models of the exchange process can be based upon realistic terminations of the bulk. Low Energy Ion Scattering (LEIS) is a method for the determination of the composition of the outermost atomic layers of materials with high precision and is thus extremely useful for the study of SOFC materials. In this contribution the principles of LEIS will be described with particular attention to their application to the conventional cathode materials such as the perovskites LSM and LSCF, and newer materials such as the Ruddlesden-Popper and double perovskite materials.
5:00 PM - B8.6/C5.6
Neutron Scattering Studies of Fluorite Structured SOFC Electrolytes.
Stefan Norberg 1 2 , Stephen Hull 2 , Sten Eriksson 1 , Dario Marrocchelli 3 , Paul Madden 4
1 Department of Chemical and Biological Engineering, Chalmers University of Technology, Gothenburg Sweden, 2 The ISIS Facility, Rutherford Appleton Laboratory, Chilton United Kingdom, 3 Department of Nuclear Science and Engineering, Massachusetts Institute of Technology, Cambridge, Massachusetts, United States, 4 Department of Materials, University of Oxford, Oxford United Kingdom
Show AbstractFuel cell technology currently attracts significant attention since these devices show considerable potential for efficient power generation in stationary, portable and transport applications. Solid oxide fuel cells (SOFCs) show much promise, given that they can use a variety of fuels such as natural gas, biogas, hydrogen, gasified coal and hydrocarbons. This variation in useable fuels, from renewable energy resources to traditional carbon based fuels, can additionally be utilised with high fuel efficiency, up to 85% for combined heat and power systems, by the direct electrochemical conversion of these fuels into electricity and heat.A core component within a solid oxide fuel cell (SOFC) is the impermeable solid electrolyte, which consists of a polycrystalline oxide ceramic operating at temperatures between 1073 K and 1273 K. The current SOFC electrolyte of choice is yttria stabilized zirconia (YSZ, Zr1-xYxO2-x/2) which for, x > 0.16, adopts the cubic fluorite phase. The oxygen anion conductivity, σ, increases with increasing x, until a maximum value (σ ~ 10-2 Ω-1 cm-1 at 1000 K) is reached at an yttria concentration close to the lower stability limit of the cubic fluorite phase. It is possible to increase the anion conductivity in YSZ by substituting Y3+ by Sc3+ and scandium stabilized zirconia (SSZ) electrolytes show good potential for use in SOFCs operating at temperatures below ~1000 K. However, from the crystal structure point-of-view, SSZ is rather more complex than its YSZ counterpart and the stability field of the highly conducting cubic fluorite structured phase is more limited in composition and temperature. An alternative to the doped zirconias is doped ceria, e.g. Ce1-xMxO2-x/2 with M = Y3+, Gd3+, etc., which also adopts the fluorite structure, but with a larger lattice constant compared to YSZ, displays higher ionic conductivities and offers the possibility of operating SOFCs at temperatures between 873 K and 1073 K.The authors have used neutron total scattering data to probe the local cation and anion ordering in numerous fluorite structured electrolytes, e.g. yttria-doped ceria, yttria- and scandia-doped zirconia, and reduced ceria, in order to access the roles of the cation-anion, cation-vacancy and vacancy-vacancy interactions determining the oxide conductivity in these systems. The results obtained by reverse Monte Carlo (RMC) analysis of the total scattering data have been correlated with impedance spectroscopy and molecular dynamics (MD) studies. The combination of RMC and MD has allowed us to carefully map out the distribution of vacancies in relation to the host and dopant cations, vacancy clustering and oxygen anions in each of these systems which makes it possible to determine the structural factors inhibiting oxygen ion conductivity. These results and their implications will be presented.
5:15 PM - B8.7/C5.7
Local Measurements of Oxygen Vacancy Content and Homogeneity in SOFC Cathode Materials from High-Resolution STEM Images.
Albina Borisevich 1 , Donovan Leonard 1 , Young-Min Kim 1 , Michael Biegalski 2 , Hans Christen 2 , Stephen Pennycook 1 , Sergei Kalinin 2
1 Materials Science and Technology Division, Oak Ridge National Laboratory, Oak Ridge, Tennessee, United States, 2 Center for Nanophase Materials Sciences, Oak Ridge National Laboratory, Oak Ridge, Tennessee, United States
Show AbstractSpatial distribution and dynamics of oxygen vacancies in the material are key parameters determining functionality of solid oxide fuel cell (SOFC) cathodes in the oxygen reduction/evolution reactions. Global chemical expansivity measurements have demonstrated that lattice parameters are very sensitive to the overall oxygen content. However, to evaluate contributions of defects and interfaces to the oxygen transport properties, we need to examine oxygen distribution at the atomic scale. Here, we describe an approach to local oxygen concentration mapping using unit-cell-by-unit-cell lattice parameter mapping by aberration-corrected Scanning Transmission Electron Microscopy (STEM). We examine lantanum/strontium cobaltite (LSCO), which was shown to exhibit good ORR activity in thin film form [1]. Several compositions of LSCO were grown by Pulsed Laser Deposition on Yttria-stabilized Zirconia (YSZ), La0.3Sr0.7Al0.65Ta0.35O3 (LSAT) and NdGaO3 (NGO) substrates. The examined films often exhibit oxygen vacancy ordering, either partial (on YSZ) or uniform (on NGO and LSAT). By mapping lattice parameters of the modulated structures, we are able to quantitatively determine local oxygen content, from the parent stoichiometric perovskite structure (La,Sr)CoO3 to highly oxygen-deficient (La,Sr)CoO2.5 brownmillerite. Lattice parameter maps and Electron Energy Loss (EELS) spectra recorded in the vicinity of grain boundaries, interfaces, and dislocations show local changes in oxygen content and electronic states. Principal Component Analysis (PCA) based statistical methods are developed for automatic determination of characteristic sizes of ordered domains and classification of the types or ordering. These studies provide insight into the phase evolution and defect chemistries in cobaltite-based SOFC cathodes under operational conditions.* This research is sponsored by the Materials Sciences and Engineering Division (AYB, DNL, YMK, SJP) and Scientific User Facilities Division (DNL, MDB, HMC, SVK), Office of BES of the U.S. DOE, and by appointment (YMK) to the ORNL Postoctoral Research Program administered jointly by ORNL and ORISE.[1] G. Jose la O’, et al., Angew. Chem. Int. Ed., 49, (2010).
5:30 PM - B8.8/C5.8
Spatially Resolving Surface Reduced Phases in SOFC Ion Conducting Materials.
Robert Walker 1 , John Kirtley 1 , David Halat 1 , Bryan Eigenbrodt 2
1 Chemistry and Biochemistry, Montana State University, Bozeman, Montana, United States, 2 Chemistry and Biochemistry, University of Maryland, College Park, Maryland, United States
Show AbstractVibrational Raman scattering, X-ray absorption spectroscopy (XAS), and electrochemical impedance spectroscopy were used to characterize the effects of ambient oxidizing and reducing atmospheres on the structural and electronic properties of high temperature ion conducting materials commonly used in SOFCs. These studies were performed in functioning devices at temperatures up to 715C. Raman scattering experiments showed that yttria stabilized zirconia (YSZ) formed a reduced phase that remained stable even when cooled to room temperature and exposed to air. This reduced phase extended approximately 5-10 nm into the bulk. Furthermore, experiments carried out under potential control show clearly that polarizing the SOFC can deplete oxide concentration even further, and this electrochemically depleted oxide region extends hundreds of microns away from the nominal electrode/electrolyte three phase boundary. Complementary ex-situ XAS data show that this surface reduced phase arises primarily from partial reduction of zirconium and not yttrium, and that the observed increase in surface conductivity is the result of excess electron density, not more facile oxide ion transport. In contrast, ceria shows behavior similar to YSZ at high temperatures, namely exposure to a reducing atmosphere leads to a surface reduction, but such a phase is not stable and can not be isolated under room temperature conditions. This observation is attributed to the mixed valence character of the cerium ion as well as ceria's smaller activation energy for oxide diffusion relative to YSZ.
B9: Poster Session II
Session Chairs
Maria Luisa Di Vona
Joshua Hertz
Philippe Knauth
Harry Tuller
Wednesday AM, November 30, 2011
Exhibition Hall C (Hynes)
9:00 PM - B9.1
Properties of Composite Membranes with S-PEEK and Nanodiamond.
Brunella Maranesi 2 1 , Hongying Hou 1 , Philippe Knauth 1 , Riccardo Polini 2 , M. Luisa Di Vona 2
2 Dip. Scienze Tecnologie Chimiche, University of Roma Tor Vergata, Roma Italy, 1 LCP-MADIREL, University of Provence, Marseille France
Show AbstractThe manufacture of composite materials can improve the properties of proton-conducting polymers used as separation membranes in PEM fuel cells. We have investigated composite membranes obtained by dispersion of nanodiamond particles in a sulfonated PEEK matrix. Sulfonated PEEK is a major proton-conducting aromatic polymer. Nanodiamond has been studied for various applications and can be functionalized with different surface groups. For use in proton-conducting membranes, surface functionalization with proton-donating groups is a promising approach. In this preliminary work, we have studied the properties of membranes made using pristine nanodiamond from diverse origins for a first assessment of the potential properties. The composites were analysed by various techniques, including Thermogravimetric Analysis, Water Vapor Uptake, Mechanical Tensile Tests and Dynamic Mechanical Analysis (DMA).
9:00 PM - B9.10
Novel Trimetallic PtIrCo Electrocatalysts for Oxygen Reduction Reaction.
Rameshwori Loukrakpam 1 , Jin Luo 1 , Bridgid Wanjala 1 , Chuan-Jian Zhong 1
1 Department of Chemistry, State University of New York at Binghamton, Binghamton, New York, United States
Show AbstractThe ability to nanoengineer the activity and stability of multimetallic alloys is important for the design of advanced fuel cell catalysts. This presentation describes the results of an investigation of PtIrCo trimetallic nanoparticle electrocatalysts supported on carbon for oxygen reduction reaction. The trimetallic nanoparticles with controllable composition and size (1-5 nm) were synthesized by nanoengineered synthesis and processing methods. Carbon-supported trimetallic nanoparticles were thermally treated in the temperature region 400-900 degree C under different reactive and non-reactive environments. The nanostructured surface and phase properties were characterized using a wide range of characterization techniques. Important insights were gained into the formation of surface oxides on the nanoparticle surfaces under different processing conditions were gained based on analysis of the XAFS and XPS data. Detailed nanostructures of the trimetallic alloy catalysts were examined with the aid of high-energy XRD studies. These catalysts were shown to exhibit enhanced electrocatalytic activity and stability for oxygen reduction reaction depending on a combination of the size, composition, lattice, and temperature parameters. The comparison between trimetallic alloy of PtIrCo and bimetallic alloys of PtIr and PtCo will also be discussed, along with their potential applications in PEMFCs.
9:00 PM - B9.11
Gold Nanoparticle Enhancement for Polymer Electrolyte Membrane (PEM) Fuel Cell.
Cheng Pan 1 , Kenny Kao 2 , Sisi Qin 1 , Miriam Rafailovich 1
1 Materials Science & Engineering, Stony Brook University, Stony Brook, New York, United States, 2 Electrical Engineering, Stanford University, Stanford, California, United States
Show AbstractPEM fuel cell technology is one of the most promising future alternative energy sources because it has relatively low operating temperature, high power density, quick response, pollution-free operation. However, its relatively low power output compared to that of its price has prevented it from many practical applications. Gold nanoparticles have been widely known to possess special capabilities. Marvrikakis et al have predicted that gold nanoparticles that are platelet shaped and have direct contact to the substrate to be the “perfect” catalysts. In our experiment, hydrophobic, thiol-functionalized and spherical gold nanoparticles (around 2nm in diameter) were synthesized through two-phase method developed by Brust et al. When a solution containing these particles is spread at the air water interface, X-ray reflectivity and EXAFS spectroscopy indicate that some of the gold atoms are removed, as the water displaces the hydrophobic thiol chains from the particle surface, resulting in platelet shaped particles. Furthermore, after these nanoparticles are spread on the surface of water in a Langmuir-Blodgett (LB) trough where surface pressure can be applied to compress them, they form LB film consisting of one or more monolayers. This LB film can then be deposited onto a solid surface, such as the Nafion membrane where the particle surface can make direct contact with electrodes and hydrogen/oxygen gases, and take effect.We find that there is an optimal surface pressure for forming gold nanoparticles monolayer to achieve the highest enhancement of output power (up to 80%). X-ray reflectivity and transmission electron microscopy (TEM) reveal the depth profiling and surface morphology of gold nanoparticles layers formed at different surface pressures. In order to determine the origin of the reaction we performed cyclic voltametry and oxygen reduction reaction measurements, but find no significant enhancement. Therefore we speculated that the reaction may be due to CO2. We measured the effect of the particles with different mixed gases and found the larger enhancement occurred only when CO2 was present. Particles were also deposited at the anode and cathode separately and the effect was only observed when the particles were at the cathode. Therefore, we think the effect of gold nanoparticles comes from inducing some reaction related to CO2. Real time detection and analysis while operating fuel cell and more electrochemistry experiments will be done to explore the exact role of gold nanoparticles.
9:00 PM - B9.12
Nanoscale Electrocatalyst Used to Improve Performance of Proton Exchange Membrane Fuel Cells.
Jingbo Liu 1 , Di-Jia Liu 2 , Zhiping Luo 3
1 Chemistry, Texas A&M University-Kingsville, Kingsville, Texas, United States, 2 The Division of Chemical Sciences, Argonne National Laboratory, Argonne, Illinois, United States, 3 Microscopy and Imaging Center, Texas A&M University, College Station, Texas, United States
Show AbstractThis study focuses on the improvement of the performance of proton exchange membrane fuel cells (PEMFCs) using platinum modified aligned carbon nanotubes (Pt-ACNT) as cathodic nanocatalyst. It was found that the PEMFC electrochemical behaviour was improved over prolonged time periods, compared to the current designs. The carbon nanotubes are prepared using chemical vapor deposition and decorated by Pt using an amphiphilic wet-chemistry method. The PEMFC devices are then constructed using these aligned Pt-ACNT as cathode. The electrochemical analyses of these devices indicate the maximum power density occurs at 860 mWcm-2 and current density reaches 3200 mAcm-2 in O2, respectively. It is important to point out that the Pt usage is decreased to less than 0.2 mgcm-2. The morphology of Pt-ACNT catalyst depicted that the diameter of CNT can be controlled within 4-15 nm and length from 8-20 µm. The unique alignment allows for rapid gas diffusion and chemisorption on the catalyst surfaces. High utilization of Pt also contributes to the PEMFC performance. The sp2 hybridization of carbon atoms provides high mechanical strength and also allows for the p electron in carbon atoms transferring to the unoccupied d-orbitals of Pt. This phenomenon can further enhance the interactions between ACNT and Pt atoms, which reinforces the stability of the cathode materials under oxidative environment. In addition to the stability of Pt- ACNTs, the hydrophobicity of the ACNTs can prevent cathode flood and favor water management, which consequently improves gas transport in the PEMFC electrode.
9:00 PM - B9.13
Microstructural Characterization of Pt-Based Nanowires for Fuel Cell Electrocatalysts.
Kelly Perry 1 , Brian Larsen 2 , Kenneth Neyerlin 2 , Bryan Pivovar 2 , Karren More 1
1 Materials Science and Technology Division, Oak Ridge National Laboratory, Oak Ridge, Tennessee, United States, 2 , National Renewable Energy Laboratory, Golden, Colorado, United States
Show AbstractPt-based electrocatalyst nanowires synthesized from Cu or Ag templates have the potential to enhance the electrocatalytic activity and durability in polymer electrolyte membrane (PEM) fuel cell cathodes. Recently, high surface area graphitized carbon and carbon nanotube supports have been investigated to impart enhanced support corrosion-resistance and improved Pt attachment to the support material; [1] however, the cathode catalyst may still degrade via several contributing mechanisms, including Pt dissolution/redeposition, Pt coalescence, and/or Pt migration. Nanowire structures may result in greater access to Pt catalytic surfaces (via extended surfaces). Previous research has been focused on the synthesis of Pt-based nanowires from Ag templates.[2,3] Pt growth on Cu nanowires by galvanic displacement has also been reported previously.[4] The galvanic displacement process used for the synthesis of these materials involves a large number of reactant variables including temperature, solvent, ligand, stoichiometry and post-processing. Analysis of different nanowire structures typically revealed a porous nature of the walls and identified residual transition metal template material. This presentation will be focused on characterizing the morphology, microstructure, and composition of Pt nanowires as related to processing conditions used and electrochemical performance. Reference:1. Wang, C.; et al. Nano Letters 4, 345 (2004)2. Sun, Y.; et al. Advanced Materials 15, 641 (2003)3. Chen, Z.; et al. Angewandte Chemie 46, 4060 (2007)4. Pivovar, B. 2011 Annual Merit Review Proceedings Fuel Cells www.hydrogen.energy.govResearch supported by the Fuel Cell Technologies Program, Office of Energy Efficiency and Renewable Energy, U.S. Department of Energy. Microscopy research supported by Oak Ridge National Laboratory’s Shared Research Equipment (SHaRE) User Facility, which is sponsored by the Office of Basic Energy Sciences, U.S. Department of Energy.
9:00 PM - B9.15
Effect of Porous YSZ Microstructure on the Performance of LDC – LST Impregnated Anode for SOFC Applications.
Milad Roushanafshar 1 , Jing-Li Luo 1 , Adrien L. Vincent 1 , Karl. T. Chuang 1 , Alan R. Sanger 1
1 Chemical & Materials Engineering, University of Alberta, Edmonton, Alberta, Canada
Show AbstractOne recently developed approach for preparing electrodes for solid oxide fuel cells is impregnation of electrode materials into a porous structure. In this method porous structures are prepared by mixing the structural material (e.g. electrolyte) with a combustible pore former before sintering at high temperature to ensure strong interparticular contact within the contiguous porous electrolyte so formed. A solution containing an electrode catalyst material then is impregnated into the porous structure, followed by calcination. This process has several advantages over alternative electrode preparation methods including: use of higher sintering temperature for preparing the porous structure, enhanced interface contact between electrode and electrolyte, synthesis of electrode material at low temperature and avoiding co-sintering of different electrode constituents. In this research the anode material was prepared by impregnation of La0.4Ce0.6O2-δ and La0.4Sr0.6TiO3±δ into a porous YSZ structure. YSZ porous structures were made by mixing YSZ (TOSOH) with different types of pore formers at different concentrations in order to vary the porosity of the structure. In addition, YSZ-TOSOH was calcined at 1600 °C to increase its particle size. Different YSZ mixtures were made by mixing the as received YSZ powders with calcined YSZ powders to determine the effect of particle size on the microstructure and electrochemical performance of their structures. Dilatometry was used to evaluate the effects of pore formers and particle size on the sintering behaviour of the structures. Scanning electron microscopy was used to investigate the microstructure development and impregnation progress. The performances of different anode structures were determined using electrochemical impedance spectroscopy methods.
9:00 PM - B9.16
Synthesis of Mesoporous Gadolinium Doped Ceria - Platinum Composite.
Hoi Yung 1 , Kwong Yu Chan 1 , Frank Leung-Yuk Lam 1
1 Chemistry, The University of Hong Kong, Hong Kong Hong Kong
Show AbstractOxygen reduction at the cathode has long been the rate determining step in solid oxide fuel cells (SOFCs) as a result of decreasing operating temperature. Mixed ionic-electronic conductors (MIECs) often used to aid cathode kinetics inevitably react with electrolyte materials in long term operations. Composite cathodes consist of ionic conductors, i.e. gadolinium doped ceria (GDC) or yttrium stabilized bismuth oxide (YSB), and electronic conductors with extended three phase boundary (TPB) has been proposed to eliminate these side reactions. We attempted here the synthesis of a mesoscale composite cathode composed of uniform channels of a fast ionic conductor, i.e. GDC impregnated with a good electronic conductor, e.g. Pt. We used KIT-6 mesoporous silica as the hard-template for GDC synthesis and chemical vapor deposition for the impregnation of the electronic conducting phase. TEM results showed good penetration of Pt into the mesoporous GDC. Unlike conventional composite cathode synthesis, the novel structure consists of mesoporous single-crystal like GDC and the connectivity of each phase is not limited by the percolation threshold. The results showed that severe surface interaction between Pt and GDC at elevated temperatures destroyed the intertwined structure. The study indicates the importance of surface interactions between electrode and electrolyte materials.
9:00 PM - B9.17
The Chemical Compatability of Ba0.5Sr0.5Co0.8Fe0.2O3-δ Cathodes for LSGM Based SOFCs.
Yeliz Ekinci 1 , Ridvan Demiryurek 2 , Cinar Oncel 2 , Nuri Solak 1 , Mehmet Ali Gulgun 2
1 Metallurgy and Material Engineering, Istanbul Technical University, Istanbul Turkey, 2 Material Science and Engineering, Sabanci University, Istanbul Turkey
Show AbstractIn this study, the compatibility of Ba0.5Sr0.5Co0.8Fe0.2O3-δ (BSCF) as a cathode material was investigated for La0.8Sr0.2Ga0.83Mg0.17O2.815 (LSGM) electrolyte based solid oxide fuel cells (SOFCs). Mixture of nickel oxide and samarium doped ceria (NiO-SDC) was used as an anode material and lanthanum doped ceria (LDC) was used as a protective layer. The SOFCs were designed as NiO-SDC/LDC/LSGM/BSCF. The chemical compatibility between the electrolyte and cathode materials was characterized by the TG/DTA, XRD, SEM and TEM/EDS techniques as function of thermal treatment time and temperature. XRD results for BSCF-LSGM mixtures showed undesired phase evolution as low as around 700 °C. Furthermore, DTA analysis showed that the reaction actually started above 400 °C. The broad dip (400 °C - 1200 °C) in the DTA curve possibly indicates a diffusional process between cathode and electrolyte materials. As a result of the long term heat treatment, we observed that LSGM electrolyte and BSCF cathode material are chemically uncompatible above 400 °C. Previously LDC (lanthanum doped ceria) protective layer was used between LSGM and NiO/SDC anode material to stop the lanthanum diffusion. It is known that LDC neither reacts with NiO/SDC nor with LSGM. LDC was suggested as a protective layer between LSGM and BSCF layers. The considered cell consists of SDC-NiO/LDC/LSGM/LDC/BSCF which can be use for intermediate temperature around or below 800 °C.
9:00 PM - B9.18
Microstructure Evolution at the Interface Region between Lanthanum Strontium Manganite Cathode and Yttria-Stabilized Ziroconia Electrolyte during Discharge Operation.
Kyosuke Kishida 1 , Haruyuki Inui 1 , Hiroki Muroyama 2 , Toshiaki Matsui 2 , Koichi Eguchi 2
1 Department of Materials Science and Engineering, Kyoto University, Kyoto Japan, 2 Department of Energy and Hydrocarbon Chemistry, Kyoto University, Kyoto Japan
Show AbstractSolid oxide fuel cells (SOFCs) composed of yttria-stabilized zirconia (YSZ) electrolyte and lanthanum strontium manganite (LSM) cathode have been studied most extensively as a model SOFC system. It has been considered that the electrochemical reactions at the cathode side of the fuel cell occur at the triple phase boundary (TPB) where the LSM cathode, YSZ electrolyte and oxidant gases are in contact with each other. Extensive studies of the SOFCs have revealed the occurrence of the so-called activation behavior at the initial stage of the SOFC operation and also the cathode side degradation under certain operation conditions. The detailed mechanisms of both the activation and degradation behavior are, however, still controversial. Since the operating temperature is very high about 1000°C, the performance of the SOFCs is greatly affected by the solid state reactions between LSM and YSZ and its resultant microstructural and compositional variations near the TPBs, the macroscopic variation of the active TPB length and so on. Most previous works on the microstructural and compositional variations at the TPB regions have been carried out using scanning electron microscopy (SEM) in this field and therefore, the nano- and submicron-scale information of microstructure and defect structure variations at the very surface of the TPBs and inside the YSZ and LSM near the TPBs are very limited. In the present study, we prepared model cells each composed of porous (La0.8Sr0.2)0.97MnO3 cathode, 8mol% Y2O3-stabilized ZrO2 electrolyte and porous Ni-YSZ cermet anode. Microstructure, defect structure and chemical composition of the TPB regions in the cathode side of the model cells were investigated transmission electron microscopy (TEM), scanning transmission electron microscopy (STEM) equipped with energy dispersive X-ray spectroscopy (EDS).Extensive amount of defects such as dislocations are observed in the YSZ grains adjacent to the LSM/YSZ interface in the as-prepared cells. These defects are totally disappeared in the specimens exhibiting the activation behavior. Since the defect concentration in the YSZ electrolyte affects its ionic conduction properties, the annihilation process of defects in the YSZ near the interface region is expected to be closely related to the occurrence of the activation behavior. In the case of the degraded cells, the surface of the YSZ electrolyte near the TPB regions are found to be covered by thin amorphous layers (~50nm in thickness) enriched with La and Mn. In addition, the crack formation at the LSM/YSZ interface and the formation of the low density regions of the LSM cathode adjacent to the interface are observed. The formation of the amorphous layer on the YSZ surface and the crack at the LSM/YSZ interface is considered to be partly responsible for the degradation of the cathode side the cells by reducing the active length of the TPBs.
9:00 PM - B9.19
Long-Term Evaluation of Candidate SOFC Materials in a 3-Cell Short Stack Geometry.
Yeong-Shyung Chou 1 , Edwin Thomsen 1 , Jung-Pyung Choi 1 , Jeffry Stevenson 1 , Gordon Xia 1 , Jeff Bonnette 1 , William Voldrich 1
1 Energy Materials, Pacific Northwest National Lab, Richland, Washington, United States
Show AbstractRefractory sealing glass, alumina coating, and Ce-modified (Mn,Co) spinel coating are currently studied as candidate materials for sealing and protective conductive coating for planar solid oxide fuel cells (SOFCs). The coating was applied via an ultrasonic sprayer onto ferritic stainless steel AISI441, followed by two steps heat treatment in different atmospheres. In order to mimic the actual SOFC conditions, the coated AISI441 interconnect plates were assembled in a 3-cell short stack using a commercial cell (Ni/YSZ supported YSZ electrolyte with LSM cathode) of 2”x2” sealed with refractory sealing glass. The short stack was tested at 800oC for long-term (6000h) at a constant current mode with mixed fuel of H2:N2=1:1 versus air. Periodic impedance and I-V sweeps were conducted at every 500h. Over the long-term testing periods, two of the three cells showed poor stability while one was rather stable with minimum degradation. Upon completion the stack was disassembled for post mortem analysis. The coated interconnect plates at sealing area and cathode site were sectioned for detailed microstructure and interfacial characterization. The stability of these candidate materials will be discussed.
9:00 PM - B9.2
Synthesis and Characterization of Polyphenylene Based Electrolytes Having Phosphonic Acid Groups.
Wataru Furihata 1 , Masahiro Yoshizawa-Fujita 1 , Yuko Takeoka 1 , Masahiro Rikukawa 1
1 Department of Materials and Life Sciences, Faculty of Science and Technology, Sophia University, Chiyoda-ku, Tokyo Japan
Show Abstract Sulfonated poly(4-phenoxybenzoyl-1,4-phenylene) (S-PPBP) is a promising polymer electrolyte material that exhibits high proton conductivity and high mechanical strength as well as Nafion® membranes. However, electrolyte membranes composed of S-PPBP result in gradual deterioration due to the low chemical stability to radicals, and show low durability in fuel cell operation. In addition, elimination of sulfonic acid groups from hydrocarbon polymers and evaporation of water around 100 °C result in a decrease of proton conductivity and in poor performance for PEFC applications. Because phosphonic acid groups exhibit higher chemical and thermal stability than sulfonic acid groups, polymer electrolyte membranes having phosphonic acid groups are expected to maintain high proton conductivity around 100 °C. In this study, we try to synthesize and evaluate hydrocarbon polymer electrolyte membranes having phosphonic acid groups. Ethyl phosphonated-2,5-dichloro-4’-phenoxybenzophenone (EP-DPBP) that had protective groups was synthesized by using palladium catalyst. The synthesis of EP-DPBP was confirmed by EI-MS, 1H NMR, FT-IR, and elemental analysis. We synthesized ethyl phosphonated poly(4- phenoxybenzoyl-1,4-phenylene) (EP-PPBP) copolymers composed of EP-DPBP and non- phosphonated monomer, 2,5-dichloro-4’-phenoxybenzophenone (DPBP) by Ni (0) coupling reaction. The contents of phosphonic acid groups of EP-PPBP copolymers calculated by H NMR spectra nearly corresponded to the theoretical values, indicating that the content of phosphonic acid groups in the copolymers was controllable by the feed ratio of the EP-DPBP and DPBP. The weight-average molecular weights of the copolymers synthesized from the ratio of EP-DPBP to DPBP was 1 : 1, 1 : 4, and 1 : 9 were 1.51 x 104, 4.05 x 104, and 5.18 x 104, respectively. TG analysis of EP-PPBP copolymers suggested that the initial and second weight loss occurred around 340 °C and 370 °C, which were associated with the removal of ethyl groups and phosphonic acid groups. The weight decreases at 340 °C and 370 °C were consistent to the ratio of the contents of ethyl groups and phosphonic acid groups. EP-PPBP copolymers exhibited high thermal stability than S-PPBP membranes. Phosphonated poly(4-phenoxybenzoyl-1,4-phenylene) (P-PPBP) copolymers was prepared by the deprotection of ethyl groups of EP-PPBP copolymers with bromotrimethylsilane. Proton conductivity and Fenton durabirity of P-PPBP copolymers were evaluated.
9:00 PM - B9.20
Poisoning Effects of SOFC Anodes by Various Alkaline-Earth Elements.
Daisuke Minematsu 1 , Sho Hashimoto 1 , Shunsuke Taniguchi 2 , Yusuke Shiratori 1 3 , Kazunari Sasaki 1 2 3
1 Faculty of Engineering, Kyushu University, Fukuoka Japan, 2 International Research Center for Hydrogen Energy, Kyushu University, Fukuoka Japan, 3 International Institute for Carbon-Neutral Energy Research (WPI), Kyushu University, Fukuoka Japan
Show AbstractIntroductionSolid oxide fuel cells (SOFCs) are attractive as e.g. the household cogeneration system and the power generation system using natural gas, biogas, and coal gas because of their several advantages including multi-fuel capability. For practical applications, we have to consider the poisoning effects by some elements during SOFC operation. For example, alkaline earth oxides may be applied to suppress coke formation on Ni-cermet anodes. Low-cost materials, which are not highly purified, are strongly required for lowering SOFC production costs. Although low-cost materials are very attractive, we cannot ignore small amount of impurities. Trace amounts of impurities may influence SOFC operation. However, almost no reports were available on the effects of such alkaline impurities. Hence, in this study, poisoning effects of SOFC anodes by alkaline-earth metals (magnesium, calcium, strontium and barium) have been analyzed using thermochemical calculation, microstructural analysis, and electrochemical measurements, in order to obtain a general overview of such poisoning effects on SOFC performance.ExperimentalTypical electrolyte-supported cells with scandia-stabilized zirconia (10 mol% Sc2O3-1 mol% CeO2-89 mol% ZrO2) (ScSZ) and Ni-ScSZ cermet anodes were used in this study. Anode powders were prepared by mixing NiO and ScSZ with a specific ratio in ethanol via ball-milling for 24 hours. Electrode layers were screen-printed on ScSZ electrolyte plates using organic binders, followed by sintering at 1300 °C for 3 hours. The anode layer consisted of 2 layers: the weight ratio of the first layer was NiO : ScSZ = 56 : 44, and that of the second layer was NiO : ScSZ = 80 : 20. For cathodes, (La0.8Sr0.2)0.98MnO3 (LSM) powders were prepared, and the cathode layers were screen-printed on the counter side of the ScSZ electrolyte plates, followed by sintering at 1200 °C for 5 hours. For reference electrodes, Pt paste was painted on the cathode side. The thickness of electrolytes was 200 μm. The electrode area was 0.8 cm by 0.8 cm (0.64 cm2).For electrochemical measurements, dry air was supplied to the cathodes, while humidified H2 was supplied to the anodes. The poisoning test was carried out by impregnating aqueous solutions of specific impurities into porous anode layers (5 mol% of Ni). Anode potential was measured at a constant current density of 0.2 Acm-2 at 800 °C.Results and DiscussionThe thermochemical calculation revealed that those elements (Mg, Ca, Sr, Ba) were stable as oxide or hydroxide, and did not react with nickel. MgO and CaO may dissolve into zirconia, while SrO and BaO may react with zirconia to form SrZrO3 and BaZrO3, respectively. These phenomena may cause long-term cell performance degradation.
9:00 PM - B9.22
Tracer Monitoring of Active and Resistive Zones for SOFC Applications.
Juergen Fleig 1 , Markus Kubicek 1 , Katharina Langer-Hansel 1 , Alexander Opitz 1 , Sandra Kogler 1 , Herbert Hutter 1
1 , TU Vienna, Vienna Austria
Show AbstractVoltage driven oxygen tracer injection into a solid electrolyte is a highly attractive method for obtaining information on electrochemically active zones at electrodes on oxide ion conductors for SOFCs. For example, it can be used to monitor the width and location of the electrochemically active regions close to three phase boundaries (TPB). In this kind of experiments avoidance of significant bulk tracer diffusion during voltage load is essential since diffusion would immediately blur the measured tracer image. Examples of such measurements are shown for oxide and metal electrodes on YSZ. Moreover, within a certain reaction path of oxygen reduction, one or more rate determining steps may be relevant and the corresponding resistive regimes can also be mapped in voltage driven 18O incorporation experiments: they manifest themselves as concentration steps or gradients. Examples of measurements on mixed conducting electrodes will be shown and among others reveal the resistive character of interfaces between electrodes and electrolytes.
9:00 PM - B9.23
Enhanced Ionic Conductivity in Oxide Superlattices with Polar Interfaces.
Seong Keun Kim 1 , Chad Folkman 1 , Matthew Highland 1 , Peter Baldo 1 , Dillon Fong 1 , Jeffrey Eastman 1
1 , Argonne National Laboratory, Argonne, Illinois, United States
Show AbstractSince quasi-two-dimensional electron gas behavior was discovered at the interface of LaAlO3 and SrTiO3, electronic phenomena occurring at polar interfaces have received considerable attention. However, the effect of polar interfaces on ionic conduction has not been investigated. We investigate in-plane ionic conduction along negatively charged interfaces in LaFeO3/SrCoO3 superlattices grown by molecular beam epitaxy. Heterostructures containing a high density of FeO2/SrO interfaces are expected to exhibit high oxygen ionic conductivity because such negatively charged interfaces require compensating charges, resulting in increased oxygen vacancy concentrations in the space charge regions. We examine the effects of temperature, oxygen partial pressure, and interface spacing on ionic conduction. Results will be compared to the electrical properties of bulk La1-xSrxCo1-yFeyO3, a well-known mixed ionic-electronic conductor. Preliminary results from an in situ X-ray scattering study of the superlattices in high temperature and variable pressure environments will also be discussed.Work supported by the U. S. Department of Energy under Contract No. DE-AC02-06CH11357.
9:00 PM - B9.24
Combinatorial Optimization of Solid Oxide Fuel Cell Cathode Composition.
Eric Fischer 1 , Peter Bocchini 1 , Joshua Hertz 1
1 Department of Mechanical Engineering, University of Delaware, Newark, Delaware, United States
Show AbstractSolid oxide fuel cells are typically operated at temperatures exceeding 800°C, requiring slow start-up and shut-down procedures, exotic gas-sealing techniques, and expensive components that house the cell itself. In recent years, significant advancements have been made in the materials and processing methods for the electrolyte. Engineering the cathodes to optimize the kinetic reaction rates is now one of the most pressing concerns for this technology. Improved cathode performance can be achieved by replacing individual electron- and ion-conducting phases with a single material capable of both forms of conduction, called a mixed ionic-electronic conductor (MIEC). A number of suitable MIEC materials are known; most of them are chemically similar and crystallize in the perovskite structure. Within these materials, a wide range of compositions can be used. Obtaining results across these compositional ranges using traditional processing is a labor-intensive procedure, and thus finding optimal compositions is a tedious trial-and-error affair.Here, we present research that uses combinatorial film growth to create thin films wherein the composition varies smoothly across the substrate. Libraries of relevant MIEC compositions were fabricated via sputtering. Characterization techniques that can be rapidly performed at many locations on the substrate will be presented. Using these techniques, optimal MIEC compositions within the fabricated libraries can be determined. More importantly, by examining the dependence of these materials parameters upon composition, testable hypotheses for their physical basis are developed. Similar techniques are expected to be broadly useful; however, the techniques do present certain limitations, which will be described.
9:00 PM - B9.3
Synthesis and Characterization of Diblock Copolymers Composed of Poly(phenylene) Derivatives.
Tatusya Oshima 1 , Kensuke Umezawa 1 , Masahiro Yoshizawa-Fujita 1 , Yuko Takeoka 1 , Masahiro Rikukawa 1
1 , Sophia University, Chiyoda-ku, Tokyo Japan
Show AbstractBlock copolymers will be expected to achieve the possibility of further controlling polymer morphology that has effective proton channels. However, the relationship between polymer morphology and proton conductivity is still unclear due to the absence of controlled all ordered structures. In order to overcome such drawback, a novel series of poly(phenylene)-based diblock copolymers with various unit ratios of hydrophilic and hydrophobic parts were synthesized by the catalyst transfer polycondensation. The relationship between microphase separated structures and proton conductivity was investigated.Diblock copolymers were synthesized with hydrophilic monomer, 2,5-dibromo-1,4-di[4-(2,2-dimetylpropoxysulfonyl)phenyl]butoxybenzene, which had neopentyl groups to protect sulfonic acid groups, and hydrophobic monomer, 2,5-dibromo-1,4-dihexyloxybenzene. These block copolymers were characterized by 1H NMR, elemental analysis, and GPC measurements. The number average molecular weights and polydispersities of the diblock copolymers were in the range of 66,300 - 82,600 g mol-1 and 1.15 - 1.32, respectively. It was found that the molecular weights of these copolymers were controllable by changing the feed ratios of monomer and catalyst. The unit ratios of hydrophilic parts and hydrophobic parts were determined by 1H NMR to be 1 : 4.5, 1 : 1.9 and 1 : 0.86, respectively. Sulfonated diblock copolymers were prepared by deprotecting neopentyl groups. Ion-exchange capacity (IEC) values of sulfonated diblock copolymers determined by back titlation were in the range of 0.84 - 2.20 meq g-1. The IEC values were consistent with the unit ratios of hydrophobic parts and hydrophilic parts. The diblock copolymers showed a low water uptake of below 20 wt. % in the range of 30 - 90% RH at 80 °C. The water uptakes of diblock copolymers decreased as the lengths of hydrophobic part increased. The diblock copolymers with the unit ratios of 1.9 : 1 and 0.86 : 1 showed similar water absorption number despite the IEC values. A variety of microphase separated structures were observed by using AFM for diblock copolymers with different unit ratios. The proton conductivity of diblock copolymers increased with increasing IEC at 80 °C and 90% RH. The diblock copolymer membrane with the highest IEC value of 2.20 meq g-1 in this study showed the highest proton conductivity of 160 mS cm-1 at 80 °C and 90% RH. The diblock copolymers with IEC values of 1.77 and 0.84 meq g-1 showed almost the same proton conductivity value at low relative humidity region despite thw IEC values.
9:00 PM - B9.4
A Novel Synthetic Method of Gold Modified Platinum Catalyst and the Application to Electrocatalyst for Fuel Cell.
Toshihiro Ikai 1 , Tomoyuki Nagai 2 , Hisao Kato 1 , Nobuaki Mizutani 1 , Tetsuo Kawamura 1 , Hajime Murata 2 , Yu Morimoto 2 , Ryosuke Jinnouchi 2
1 Metallic & Inorganic Material Engineering, Toyota Motor Corporation, Toyota-cho, Aichi-prefecture, Japan, 2 Electorochemistry Div., Toyota Central R&D Labs., INC., Nagakute, Aichi-prefecture, Japan
Show AbstractGold (Au) modified Platinum (Pt) nano-particle as electrocatalyst has been studied to reduce Pt amount in fuel cell by restraining Pt degradation. In order to modify Au selectively onto Pt surface, one atomic layer of cupper (Cu) was firstly deposited onto Pt surface. Then, Au was modified on Pt by exchanging Au with Cu. A novel synthetic method for catalyst scale-up was found by developing a simple and low-cost Cu deposition technique. Under Potential Deposition (UPD) is a suitable method to deposit one atomic layer of Cu onto Pt, which enable Cu reduce at higher potential than redox potential of Cu by interaction with Pt substrate. For a simple UPD process, the method to apply equilibrium potential between CuSO4 aqueous solution and Cu wire was studied, while the potentiostat is often used to control the potential. Firstly Pt nano-particle deposited carbon black was dispersed in CuSO4 aqueous solution saturated with nitrogen gas. Contacting Pt with Cu wire during agitation caused Cu dissolution from Cu wire by the potential difference between Pt and Cu, then Cu ion in the solution was reduced and deposited on Pt surface. The electrochemical analysis indicated one atomic layer of Cu was successfully deposited onto Pt. Secondly Cu deposited Pt particle on carbon black was dispersed in HAuCl4 aqueous solution to exchange Au with Cu by the difference in redox potential. Au modified Pt catalyst as a product showed better durability during potential cycling test than conventional catalyst, and possibility to reduce Pt amount in fuel cell.
9:00 PM - B9.5
Proton-Conducting Cross-Linked Sulfonated Aromatic Polymers for Fuel Cells Application.
Maria Luisa Di Vona 1 , Brunella Maranesi 1 , Luca Pasquini 1 , Philippe Knauth 2
1 , Dip. Scienze e Tecnologie Chimiche, University of Rome Tor Vergata, Rome Italy, 2 , Université de Provence, Marseille France
Show AbstractThermal stability, hydration and mechanical properties of thermally cross-linked Sulfonated Aromatic Polymers (SAPs) with high ionic exchange capacity (IEC) were measured and compared to untreated samples. The formation of cross-linking greatly stabilizes SAPs in terms of thermal, mechanical, and hydrolytic degradation: they can resist in water even at a temperature of 145 °C with improved mechanical properties. Elemental analysis, acid-base titration, and FTIR spectra consistently indicate that the SAP microstructure stabilization is related to cross-linking of the polymer chains by SO2 bridges, which is promoted by temperature. The analysis by stress–strain tests and Dynamic Mechanical Analysis shows also a large increase of glass transition temperature and mechanical strength. The new method for introducing a certain degree of covalent bonds between adjacent polymeric chains by heat treatment of cast membranes is really economic, since the cross-linking reaction can be performed directly after membrane casting. Due to its simplicity, it is furthermore very suitable for industrial preparation of cross-linked membranes, because the procedure can be easily up-scaled. However, a delicate balance still exists between the hydrophilic character of membranes and their properties.References: 1. M. L. Di Vona et al. J. Phys. Chem. B, 113, 7505–7512 (2009). 2. M.L. Di Vona et al. J. Memb. Sci., 354, 134-141 (2010).
9:00 PM - B9.6
Ternary PtSnRh–SnO2 Nanoclusters: Synthesis and Electroactivity for Ethanol Oxidation Fuel Cell Reaction.
Wenxin Du 1 , Qi Wang 2 , Carlo LaScala 1 , Lihua Zhang 3 , Dong Su 3 , Anatoly Frenkel 4 , Virendra Mathur 1 , Xiaowei Teng 1
1 Department of Chemical Engineering, University of New Hampshire, Durham, New Hampshire, United States, 2 Department of Chemical Engineering, University of Delaware, Newark, Delaware, United States, 3 Center for Functional Nanomaterials, Brookhaven National Laboratory, Upton, New York, United States, 4 Department of Physics, Yeshiva University, New York, New York, United States
Show AbstractEthanol is a promising fuel for low–temperature direct fuel cell reactions due to its low toxicity, ease of storage and transportation, high energy density, and availability from biomass, compared to hydrogen and methanol. However, the lack of effective electrocatalysts for ethanol oxidation reaction is a major hindrance for the commercialization of direct ethanol fuel cell (DEFC) technology. Recently, several studies have indicated that the synergistic effect in ternary systems may render a better electrocatalyst for ethanol oxidation reactions. Here we have systematically studied a series of Pt/Rh/Sn electrocatalysts for the ethanol oxidation reactions. We report the synthesis of carbon supported ternary Pt/Rh/Sn electrocatalyst with the average diameter of less than 3 nm through a Polyol process. Several complementary characterization techniques including high resolution transmission electron microscopy (HRTEM), X-ray diffraction (XRD) and extended X-ray absorption fine structure (EXAFS) were used to identify the coexistence of homogeneously distributed Pt/Sn/Rh random alloy and non-alloyed SnO2 throughout the catalyst. The PtRhSn/C catalyst showed a superior long-term activity and stability towards ethanol oxidation than the commercial Pt catalyst (ETEK). Our data also indicated that the superior performance of PtRhSn/C might result from the electronic effect of the Pt/Sn/Rh random alloy. In particular, both Pt and Rh sites showed more filled d band structure upon homogeneously alloying with Sn, which could mitigate Pt sites from poisoning due to the weak binding to the blocking intermediates. Our study well correlates the structure-property relation of PtRhSn/C in ethanol electro-oxidation, and thus may afford an avenue for designing more effective electrocatalysts in the future. This work has been published in the Journal of Materials Chemistry in May 2011 (Wenxin Du, Qi Wang, Carlo A. LaScala, Lihua Zhang, Dong Su, Anatoly I. Frenkel, Virendra K. Mathura, and Xiaowei Teng, Ternary PtSnRh–SnO2 nanoclusters: synthesis and electroactivity for ethanol oxidation fuel cell reaction. Journal of Materials Chemistry, 2011, 21, 8887-8892).
9:00 PM - B9.7
High Performance Pt Electrocatalyst Well Dispersed in Mesoporous Carbon Support Synthesized via an Unconventional Route of Carbonization over PFA-Protected Dispersed Platinum.
Fujun Li 1 , Kwong-Yu Chan 1 , Hoi Yung 1
1 Chemistry, University of Hong Kong, Hong Kong Hong Kong
Show AbstractOrdered mesoporous carbons, e.g. CMK-3 have been widely investigated as supports for fuel cell catalysts. These structures are synthesized via carbonization of mesoporous silica templates impregnated with a carbon precursor such as sucrose or furfuryl alcohol. Loading Pt and PtRu into the high surface area mesoporous carbon supports faces imperfections of clustering metal nanoparticles, loss of Pt from precursor, and uneven composition of Pt:Ru. An alternative and effective route of synthesizing mesoporous carbon supported Pt nanoparticles is introduced here to overcome these problems. In reverse order to the conventional synthetic route of ethylene glycol method, carbonization occurs after dispersion of platinum. In this process, H2PtCl6 acts as a Pt source and serves as a catalyst for the polymerization of furfuryl alcohol (FA). The polymerized FA around the H2PtCl6 nanoparticles functions as a protecting agent and prevents the growth of Pt nanoparticles in the later high temperature carbonization step. The resulting Pt nanoparticles are highly dispersed in the mesoporous carbon structure, CMK-3, and give a much higher methanol oxidation current when compared with Pt/CMK-3 electrocatalyts prepared via the conventional route.Extending the method to synthesize CMK-3 supported PtRu nanoparticles has achieved high dispersion, uniform composition of Pt:Ru, and high activity towards methanol oxidation. Reference: Fujun Li, Kwong-Yu Chan* and Hoi Yung, "Carbonization over PFA-Protected Dispersed Platinum: An Effective Route to Synthesize High Performance Mesoporous-Carbon Supported Pt Electrocatalyst" J. Mater. Chem. (2011)
9:00 PM - B9.8
Pt Dissolution Behavior of SnO2-Supported PEFC Electrocatalysts.
Yuma Takabatake 1 , Fumiaki Takasaki 1 , Zhiyun Noda 2 , Yusuke Shiratori 1 3 , Shunsuke Taniguchi 2 , Akari Hayashi 2 3 , Kazunari Sasaki 1 2 3
1 Faculty of Engineering, Kyushu university, Fukuoka Japan, 2 International Research Center for Hydrogen Energy, Kyushu university, Fukuoka Japan, 3 International Institute for Carbon-Neutral Energy Research (WPI), Kyushu university, Fukuoka Japan
Show AbstractIntroduction Polymer electrolyte fuel cells are promising power sources for vehicles, co-generation systems, and mobile devices. The durability of their electrocatalysts is one of the most important technological issues. Especially, Pt electrocatalysts supported on carbon materials are suffered from carbon corrosion on the cathode side especially under the start-up and shut-down condition. We are developing cabon-free Pt electrocatalysts using SnO2 as the electrocatalyst support material. The use of SnO2 as an alternative support improves durability under the start/stop voltage cycling, as SnO2 is thermochemically stable under the operational condition. We have reported that the durability test with voltage cycles between 0.9 and 1.3 V revealed that the Pt electrocatalyst supported on SnO2 maintained electrochemical surface area (ECSA) even after 60,000 voltage cycling. Pt dissolution is another major factor causing electrocatalyst degradation. The aim of this study is therefore to clarify the Pt dissolution behavior for SnO2 support.Experimental SnO2 powders were prepared by the co-precipitation procedure. Pt nano-particles were then impregnated on SnO2 by the colloidal method. Pt loading was set to be 20 wt. %. For comparison, Pt-based electrocatalysts supported on carbon black (Vulcan) were prepared by the same colloidal procedure.The Pt dissolution into the electrolyte solution was determined using a three-electrode cell. Cyclic voltammetry was applied to evaluate electrochemical characteristics of the catalysts. In this study, ECSA was determined by hydrogen desorption region obtained in the CV measurements. Durability of the catalysts under the cathode conditions was evaluated by measuring the change in ECSA. In the durability tests, electrocatalysts were subjected to the potential cycles between 0.6 and 0.9 V, where Pt dissolution will occur. After the durability tests, the concentration of Pt in the HClO4 electrolyte solutions was measured by Inductively Coupled Plasma Atomic Emission Spectrometer analysis (ICP-AES). Results and Discussion At the initial stage, ECSA of Pt supported on SnO2 -based materials increased with the number of cycles, followed by a gradual decrease. In the durability tests for Pt/SnO2, Pt/Sn0.98Nb0.02O2, and Pt/C electrocatalysts, the decreasing rates of ECSA were almost independent of support materials. The fraction of Pt dissolved into the electrolyte solution was less than 10% of total Pt supported on the electrocatalysts studied in this study after 10,000 voltage cycles. Pt/SnO2 maintained ca. 80% of Pt even after 60,000 cycles.
9:00 PM - B9.9
Synthesis of Tungsten Carbide and Catalytic Activity of Gold Palladium Platinum on a Tungsten Carbide Support.
Ming Nie 1 , Zhijun Zeng 1 , Qing Li 1 , Xiaoqin Liao 2 , Lizhao Qin 1
1 School of Materials Science and Engineering, Southwest University, Chongqing China, 2 School of Foreign Language, Southwest University, Chongqing, Chongqing, China
Show AbstractThe development of different fuel cells require high property catalytic materials. This report describes the findings of nanoengineered platinum composite catalysts. The catalysts were synthesized by an intermittent microwave heating (IMH) method at an optimized ratio of tungsten to carbon. Examples shown in this report included AuPdPt-WC/C catalysts. By comparison, these novel electrocatalysts could offer the activities that surpass that of the commercial electrocatalysts for oxygen reduction reaction. This phenomenon shows that we have found new composite catalysts. The advantage seemed to come from the interaction between multi-metallic compositions and tungsten carbide which has the capability to enhance the catalytic activity of the metal electrocatalysts. The mechanism of the composite catalysts will also be discussed.
Symposium Organizers
Maria Luisa Di Vona University of Rome Tor Vergata
Joshua Hertz University of Delaware
Philippe Knauth University of Provence
Harry L. Tuller Massachusetts Institute of Technology
B10/C6: Joint Session: SOFC Materials Characterization II
Session Chairs
Wednesday AM, November 30, 2011
Constitution B (Sheraton)
9:30 AM - B10.1/C6.1
Measuring Oxygen Reduction/Evolution Reactions in Fuel Cells on the Nanoscale.
Amit Kumar 1 , Francesco Ciucci 2 , Anna Morozovska 3 , Sergei Kalinin 1 , Stephen Jesse 1
1 CNMS, Oak ridge National laboratory, Oak ridge, Tennessee, United States, 2 Interdisciplinary Center for Scientific computing, University of Heidelberg, Heidelberg Germany, 3 Institute of semiconductor physics, National academy of science of Ukraine, Kiev Ukraine
Show AbstractSolid oxide fuel cells (SOFC) based electrochemical energy conversion systems are one of integral components of current and future energy technologies. The energy conversion in these systems is underpinned by ion and vacancy diffusion, electronic transport and solid-gas and solid-liquid reactions at surfaces and triple phase junctions. One of the critical steps in the SOFC and Li-air battery operation leading to large overpotentials and charge-discharge hysteresis is the kinetics of the oxygen oxidation reaction (ORR). It is important thus to explore the mechanisms behind this enhancement which remain elusive, largely due to the lack of experimental techniques capable of probing ORR on the nanoscale. Oxygen vacancies play a significant role in determining the functionality of electro-resistive devices, non-volatile memories based on resistive switching and solid oxide fuel cells. Traditionally, the study of the role of oxygen vacancies in these processes is limited by high activation temperature and macroscopic measurement techniques. Here, we demonstrate spatially resolved local probing of the thermodynamics and kinetics involving the generation and diffusion of oxygen vacancies by utilizing chemical expansivity of these oxides upon application of concentrated electric fields. Using Band excitation Electrochemical strain microscopy (ESM), a strongly confined electric field at tip is used to drive the oxygen vacancies in these oxide materials and the resulting localized electrochemical strain is detected. A high frequency periodic bias is applied on the oxide material and the PFM tip acts as a probe of the local displacement arising due to migration of oxygen vacancies. Local strain hysteresis loops driven by vacancy diffusion have slow dynamics and thus open up. Mapping the loop opening as a function of the final bias allows establishment of the onset and kinetics of the diffusion process. Signal relaxation measurements enable us to locally characterize the diffusion dynamics of the vacancies. In mixed ionic-electronic oxide systems, we also utilize current-voltage measurements to probe the electronic transport . Correlated mapping of the local oxygen vacancy movement and diffusivity has been achieved with a resolution of ~ 30 nm. The mapping of vacancies is shown on purely ionic oxides (Yttrium stabilized zirconia and Samarium doped Ceria). Systematic mapping of ORR/OER activity on bare and Pt-functionalized yttria-stabilized zirconia (YSZ) surfaces is demonstrated. This approach allows directly visualization of ORR\OER activation process at the triple-phase boundary. Acknowledgement : This material is based upon work supported by research division of Materials Science and Engineering, Office of basic energy sciences, DOE.
9:45 AM - B10.2/C6.2
Highly Anisotropic Oxygen Adsorption and Incorporation Kinetics on (La,Sr)2CoO4+δ Surfaces and Hetero-Interfaces.
Jeong Woo Han 1 , Bilge Yildiz 1
1 Laboratory for Electrochemical Interfaces, Department of Nuclear Science and Engineering, Massachusetts Institute of Technology, Cambridge, Massachusetts, United States
Show AbstractA2BO4 Ruddlesden-Popper family of materials is being considered as interesting cathode candidates for intermediate temperature solid oxide fuel cells (SOFCs) due to the fast oxygen transport in them. Furthermore, recent reports have demonstrated distinctly enhanced oxygen reduction rate (ORR) at the hetero-interface of (La,Sr)CoO3 and (La,Sr)2CoO4+δ, but the mechanism for such enhancement is not yet known. To unravel the governing mechanism for the ORR activity enhancement at this interface, we first investigate the oxygen surface reactions on LaCoO3 (LCO113) and La2CoO4+δ (LCO214) as reference systems, and then probe the same interactions at the hetero-interface of LCO113/LCO214. We recently reported the static and kinetic energetics of the oxygen incorporation and transport on strained LCO113 surfaces, and the interstitialcy diffusion of oxygen in bulk LCO214. Complementary to those results, here we assess the O2 adsorption on and incorporation into the LCO214 surfaces. We perform first principles-based calculations in the density functional theory (DFT) formalism, to provide an atomic scale view of the adsorption and incorporation mechanisms and kinetics. We identified the reaction sites and energies for the O2 adsorption, its dissociation on LCO214 surface and incorporation into the subsurface. Atop La cation in the vicinity of the interstitial path between the LaO planes on LCO214(100) is a significantly stronger adsorption site than on the CoO2 layer terminated on LCO214(001) (that is equivalent to the LCO113(001) surface). Upon adsorption, O2 dissociates into the interstitialcy path, with an energy barrier (0.77 eV) similar to that of dissociation on the LCO113(001) surface and of oxygen migration barrier in the bulk LCO214 and LCO113. Furthermore, lattice strain at the LCO214/LCO113 heterointerface (on LCO214(100)) strengthens the adsorption, and at the same time provides larger space for oxygen incorporation. These two processes balance, and thus, no effective improvement is found for the dissociation and incorporation with increasing tensile strain. Based on our results, the strongly favored adsorption on the (100) plane of LCO214 plays a major role on the recently reported enhancement of the ORR near the LCO214/LCO113 interface, which has the LCO214(100) surface exposed to oxygen.
10:00 AM - B10.3/C6.3
First Principles Kinetic Monte Carlo Simulations of the Interaction of Oxygen with LaMnO3 Surfaces.
Ghanshyam Pilania 1 , R. Ramprasad 1
1 Materials Science, University of Connecticut, Storrs, Connecticut, United States
Show AbstractPerovskite type lanthanum based transition metal oxides are frequently explored as the cathode material for solid oxide fuel cells (SOFCs). Their utility in SOFCs derives from their ability to catalyze the oxygen reduction reaction (ORR), as well as their low cost, high-temperature stability, and adequate thermal expansion properties. Apart from their use in SOFCs these materials are also promising for many other technologically important applications such as photocatalysis and for removal of NOx gases in diesel engine auto-exhausts. The underlying processes in all the above mentioned applications involve interaction of the perovskite surface with the gas phase oxygen. Therefore, acquiring a fundamental understanding of the nature of the interaction between oxygen and the perovskite surfaces is crucial to explain the role of oxygen in such technological processes.Experimental techniques such as temperature programmed desorption and reaction spectroscopies are employed to provide useful insights into the binding energetics of adsorbates or reactants at the solid surfaces. However, the obtained experimental data contains only a limited amount of information on the spatial arrangement of the surface species at a given temperature and pressure. More importantly, such techniques cannot directly distinguish between the various possible elementary or help in the identification of the rate limiting steps involved. Here we have employed first-principles based kinetic Monte Carlo (kMC) simulations to investigate the relative stability of the clean as well as molecular and atomic oxygen covered LaMnO3 surfaces over a vast range of temperatures and oxygen partial pressures. For definiteness, the (001) MnO2-terminated surface was considered. The energetics as well as the activation energies of various surface reactions were computed using density functional theory. The elementary surface reactions included adsorption, desorption, surface dissociation, and the surface diffusion of molecular and atomic oxygen. The computed energetics and barriers were then used in large-scale kMC simulations to predict the surface oxygen content and configuration at various combinations of temperature and pressure, thereby yielding a surface phase diagram. Owing to the state-of-the-art theory, algorithms and computations employed, these results are believed to represent the real situation with high fidelity. On the basis of our surface phase diagram results, we are able to identify the conditions most favored for the dissociative adsorption of molecular oxygen. These are (temperature and pressure) conditions corresponding to partial atomic oxygen coverage. In other words, the “phase boundaries” as predicted by our kMC simulations are identified to be the catalytically active regions for ORR. Our methodology will be applied to study doped oxides (e.g., LSM), and may effectively be used to design materials with enhanced activities at predetermined temperatures and pressures.
10:15 AM - B10.4/C6.4
Structural Characterization of Epitaxial Fluorite-Type Solid Electrolyte Thin Films.
Weida Shen 1 , Jun Jiang 1 , Joshua Hertz 1
1 Department of Mechanical Engineering, University of Delaware, Newark, Delaware, United States
Show AbstractThin film electrolytes are being heavily investigated within both fundamental studies as well as for practical use within thin film and bulk devices. The structural and crystallographic properties of thin films are often highly dependent upon the substrate and growth conditions. As these properties are suspected to consequently affect the electrochemical properties of the films, determination of the processing-property relationships are critical to understanding and, ultimately, improving device performance. Complicating this understanding, in part, is the lack of highly suitable substrates with a close lattice match to the typical fluorite-type solid electrolytes, ceria and zirconia. Here, we present microstructural and crystallographic characterization of films deposited via sputtering onto heteroepitaxial substrates. Particular attention is paid to the presence of lattice strains and interfacial regions with a high concentration of planar defects, as these are supposed causes for the recent reports of high apparent conductivity in these films.
10:30 AM - B10.5/C6.5
Measurement of the Debye Screening Length in an Oxide Ion Conductor.
Marisa Frechero 1 2 , Mirko Rocci 1 , Rainer Schmidt 1 , Mario Diaz-Guillen 1 , Oscar Dura 1 , Alberto Rivera-Calzada 1 , Jacobo Santamaria 1 , Carlos Leon 1
1 Fisica Aplicada III, Universidad Complutense Madrid, Madrid Spain, 2 , On leave from Dpto Quimica- Universidad Nacional del Sur, Bahia Blanca Argentina
Show AbstractBroadband dielectric spectroscopy experiments in a bicrystal of the oxide ion conductor 9 mol % yttria stabilized zirconia (YSZ) with a symmetrical -12°/12° [110] tilt grain boundary have allowed us to measure and characterize ion transport across a single grain boundary. We have obtained important microscopic parameters that determine ion transport properties at the nanoscale such as the built-in potential at the interfacial plane, the space charge layer thickness, and the Debye screening length. The values are found to be in remarkable agreement with the predictions of simple theoretical space charge models, in contrast to previous estimates from measurements on polycrystalline YSZ ceramic samples of similar composition.
11:15 AM - **B10.6/C6.6
Geometrically Asymmetric Electrodes for Probing Electrochemical Reaction Kinetics.
Sossina Haile 1 , Yong Hao 1 , Kenji Sasaki 1 , Mary Louie 1 , WooChul Jung 1
1 , Caltech, Pasadena, California, United States
Show AbstractElectrochemical reactions can exhibit considerable asymmetry, with the polarization behavior of oxidation at a given electrode differing substantially from that of reduction. The reference-less, microcontact electrode geometry, in which the electrode overpotentials are geometrically constrained to the working electrode (by limiting its area) is experimentally convenient, particularly for fuel cell studies, because the results do not rely on accurate placement of a reference electrode nor must oxidant and reductant gases be sealed off from one another. Here, the conditions under which the critical assumption of this geometry applies – that the overpotential at the large-area counter electrode can be ignored – are numerically assessed. Several experimental examples of insight gained from this method are presented.
11:45 AM - B10.7/C6.7
Unreliability of the Simultaneous Determination of kchem and Dchem through Conductivity Relaxation.
Rosemary Cox-Galhotra 1 , Steven McIntosh 1 2
1 Chemical Engineering, University of Virginia, Charlottesville, Virginia, United States, 2 Chemical Engineering, Lehigh University, Bethlehem, Pennsylvania, United States
Show AbstractElectrical conductivity relaxation is utilized to determine the oxygen surface exchange coefficient, kchem, and bulk oxygen diffusion coefficient, Dchem, of mixed ionic and electronic conducting oxides for solid oxide fuel cell cathodes. In this technique, the conductivity of a dense sample is recorded during an instantaneous step change in gas-phase pO2. Bar samples of material are typically utilized, and kchem and Dchem are extracted from each data set. In this study we examine the reliability of this simultaneous fit procedure for bar samples of La0.6Sr0.4Co0.2Fe0.8O3-δ (LSCF 6428). We suggest that discrepancies in the literature reported values of these parameters are due to the existence of multiple solutions to the data fit, which render this technique unreliable for bulk samples. To obtain accurate values of kchem and Dchem, the sample thickness must be varied significantly such that analysis occurs completely in the kchem regime (thin film) or Dchem regime (thick sample) and the number of adjustable parameters collapses to one.LSCF 6428 was synthesized using a modified Pechini procedure. The powder was calcined, pressed into pellets and sintered at 1523K for 12 h. Bar samples 1.2 cm x 0.5 cm x ~0.07 cm were cut from these dense (>95% theoretical), polished pellets and four-point Au conductivity contacts attached. Relaxation measurements were performed in six logarithmically spaced pO2 steps from 100% to 3.3% O2. Full details available elsewhere [1].The values of kchem and Dchem for LSCF 6428 determined in our study were within one to two orders of magnitude greater than those previously reported [2,3]. Direct comparison of our electrical conductivity data with published values [3] suggested that our sample was nominally identical. Furthermore, measurements on samples prepared identically yielded results within 0.1 orders of magnitude. The samples do not appear to be problematic. We then turned our attention to the fitting procedure and investigated the influence of the number of roots determined on the resulting values of kchem and Dchem. We found a strong variation in especially kchem with the number of roots, but no significant change in the quality of the fit. From this we conclude that the simultaneous determination of both parameters from a single data set is flawed due to the presence of multiple, equally correct solutions of kchem and Dchem. As mentioned previously, using thin film samples for conductivity relaxation allows Dchem to be eliminated from the analysis, resulting in a one-parameter fit of kchem. We will demonstrate this method for dense, polycrystalline thin film samples of the layered perovskite PrBaCo2O5+δ (PBCO), deposited onto SrTiO3 substrates using spray pyrolysis. References[1] R. Cox-Galhotra and S. McIntosh, Solid State Ionics,181 (2010) 1429.[2] H.J.M. Bouwmeester, et al., J. Solid State Electrochem., 8 (2004) 599.[3] J.A. Lane, et al., Solid State Ionics, 121 (1999) 201.
12:00 PM - B10.8/C6.8
Detailed Electrochemical Analysis of Nanoscaled La0.6Sr0.4CoO3-δ as Intermediate Temperature SOFC Cathode.
Jan Hayd 1 3 , Levin Dieterle 2 3 , Dagmar Gerthsen 2 3 , Andre Weber 1 , Ellen Ivers-Tiffee 1 3
1 Institut für Werkstoffe der Elektrotechnik (IWE), Karlsruher Institut für Technologie (KIT), Karlsruhe Germany, 3 DFG Center for Functional Nanostructures (CFN), Karlsruher Institut für Technologie (KIT), Karlsruhe Germany, 2 Laboratorium für Elektronenmikroskopie (LEM), Karlsruher Institut für Technologie (KIT), Karlsruhe Germany
Show AbstractLow-temperature operation (400 to 600 °C) of solid oxide fuel cells has generated new concepts for materials choice, interfacial design and electrode microstructures. Nanoscaled and nanoporous La0.6Sr0.4CoO3-δ thin film cathodes derived from metal-organic precursors (metal organic deposition, MOD) with a film thickness of 200 nm and an average grain and pore size in the sub 100 nm regime were investigated with the focus on the reaction kinetics by a systematic temperature (T = 400 – 600°C) and oxygen atmosphere (pO2 = 0.01 – 0.5 atm) variation. Electrochemical impedance spectroscopy was applied, followed by a detailed data analysis including calculating the distribution function of relaxation times (DRT) and CNLS fit. Five processes were identified. Four processes are temperature activated, whereas one process at low frequencies exhibits a slight deactivation with temperature. Furthermore, the three low and mid frequency processes are oxygen partial pressure dependent, whereas the two high frequency processes remain unaffected by pO2 variations. We report a record performance for nanoscaled LSC cathodes of 9 mΩxcm2 at 600 °C, 75 mΩxcm2 at 500 °C and 1.95 mΩxcm2 at 400 °C, measured in synthetic air. These results were, in the most part, facilitated by a substantial increase of the inner surface area of the porous thin film cathode, but also nanoparticulate Co3O4 might be the cause of further enhanced oxygen exchange kinetics.
12:15 PM - B10.9/C6.9
Investigation the Rate Determining Steps of Oxygen Reduction on LSCF Cathode Using Nonlinear EIS.
Ning Xu 1 , Jason Riley 1 , John Kilner 1 , Cortney Kreller 2
1 Materials, Imperial College London, London United Kingdom, 2 Chemical Engineering, University of Washington, Seattle, Seattle, Washington, United States
Show AbstractLanthanum cobaltite substituted with strontium and iron, La0.6Sr0.4Co0.2Fe0.8O3-δ (LSCF), has attracted much attention as a promising candidate for intermediate temperature solid oxide fuel cells (IT-SOFC) in the past decade, [1] [2] because of its high mixed ionic-electronic conductivity and good thermal stability. As a consequence of the high ionic-electronic conductivity, oxygen reduction can take place competitively along the surface of the LSCF grains and/or through the bulk of the electrode material. [3] A systematic understanding of the rate limiting processes under different operation conditions has yet to be achieved.Compared to the traditional electrochemical impedance spectroscopy (EIS), nonlinear EIS (NLEIS) has been demonstrated to be more powerful in separating entangled mechanisms and distinguishing theoretical models with subtle differences. Wilson et al. [4] [5] performed NLEIS analysis on strontium-doped lanthanum cobaltite (LSC) and revealed that O2 reduction on this cathode material is limited by dissociative adsorption.In this work, NLEIS measurements are adopted as an extension to the polarization dependent EIS measurements which were performed on a symmetric cell with gadolinium-doped ceria (CGO) as the electrolyte. LSCF ink made from ball-milling commercial powder with ink vehicle was screen-printed onto both sides of a dense CGO pellet (sintered at 1200 oC for 5h) to form a symmetric cell. Cross sectional SEM was used to characterize the microstructure of the electrode-electrolyte interface. Cross-sectional SEM was used to characterize the microstructure of the electrode-electrolyte interface. Obvious distortions were found between the EIS results under different excitations when the cell is operated in the low temperature regime (<500 oC), while no distortions were observed at high temperature (>700 oC); this might imply a switch of the dominant process. The dominant process of low operation temperature is therefore more nonlinear. NLEIS measurements were then carried out at the same temperature points, the results of which showed very interesting features in harmonic responses. For example, the appearance of appreciable even harmonic responses on the symmetric cell suggests an asymmetric anodic/cathodic mechanism. Moreover, harmonic responses were also detected at high temperature with similar amplitudes to those at low temperature in NLEIS; whereas in the polarization dependent EIS results, the nonlinearity at high temperature was completely masked by the increased fundamental response.[1] A. Esquirol, N. Brandon, J. Kilner, and M. Mogensen, J. Electrochemical Society, 151 (2004) 1847;[2] J. Lane, S. Benson, D. Waller and J. Kilner, Solid State Ionics 121 (1999) 201;[3]M. Prestat, J. Koenig and L. Gauckler, J. Electroceram 18 (2007) 87;[4] J. Wilson, M. Sase, T. Kawada and S. Adler, Electrochemical and Solid-State Letters 10 (2007): 86;[5] J. Wilson, D. Schwartz and S. Adler, Electro. Acta, 51 (2006), 1389.
12:30 PM - B10.10/C6.10
A New La0.5Sr0.5Mn0.5Co0.5O3-δ Anode for Low-temperature Solid Oxide Fuel Cells.
Ainara Aguadero 1 2 , Domingo Perez-Coll 3 , Jose Antonio Alonso 1 , Stephen Skinner 2 , John Kilner 2
1 , ICMM-CSIC, Madrid Spain, 2 Materials, Imperial College London, London United Kingdom, 3 , ICV-CSIC, Madrid Spain
Show AbstractIn this work we have developed a new oxygen-defective La0.5Sr0.5Mn0.5Co0.5O3-δ perovskite as an anode for low temperature solid oxide fuel cells (SOFC) (< 600 C). The reduction of the oxygen-stoichiometric La0.5Sr0.5Mn0.5Co0.5O3-δ perovskite oxide at 500 C for 6h leads to a hypostoichiometric phase with oxygen hypostoichiometry of δ = 0.6(1) oxygen atoms per formula unit. The neutron power diffraction study reveals a slight deviation from the cubic symmetry that can be structurally defined in the Pbnm space group, with a random distribution of the metals over the A and B positions of the perovskite and oxygen vacancies. The quantity of oxygen refined in the structure is O2.52(2) with high values of isotropic thermal factors (up to 4.5(4) Å2 for O1 and 6.3 (1) Å2 for O2) in the 150 to 600 C temperature range indicating significant mobility of oxide ions in this structure; on the other hand, this material has shown an extraordinary reaction rate and selectivity for the conversion of alkylaromatics, for instance p-xylene in TPA, with respect to the standard homogeneous catalyst [1]. The thermal expansion coefficient has been observed to be around 14x10-6 K-1 while the polarization resistance values with ceria-based electrolytes in H2(10%) vary from 0.02 to 2 Ωcm2 in the 600 to 350 C temperature range, suggesting this material as a promising low-temperature SOFC anode.[1] A. Aguadero, H. Falcón, J. M. Campos-Martín, J. L. García-Fierro, J. A. Alonso Angewandte chemie international edition. Accepted DOI : 10.1002/anie.201007941
B11: PEM Membranes II
Session Chairs
Wednesday PM, November 30, 2011
Constitution B (Sheraton)
2:30 PM - **B11.1
New Hybrid Inorganic-Organic Proton Conducting Membranes Based on Nafion and [(ZrO2)*(Ta2O5)0.119] Oxide Core-Shell Nanofiller.
Vito Di Noto 1 , Matteo Piga 1 , Enrico Negro 1 , Guinevere Giffin 1 , Sandra Lavina 1
1 Department of Chemical Sciences, University of Padova, Padova, Padova, Italy
Show AbstractThe current state-of-the-art proton-conducting membranes for application in fuel cells and electrolysers are perfluorinated ionomers such as Nafion® and Aquivion®. These materials feature excellent chemical and electrochemical stability and very high proton conductivity in fully-hydrated conditions. However, perfluorinated ionomers do not yield good performances in a dry state and at temperatures higher than 80-90°C. To overcome these deficiencies, a new family of hybrid inorganic-organic membranes based on Nafion and a “core-shell” nanofiller consisting of ZrO2 nanoparticles acting as the “core” covered by a thin layer of Ta2O5 as the “shell” is proposed. Six hybrid membranes with a nanofiller content of 3, 5, 9, 11, 13 or 15 wt% are prepared by a standard solvent-casting procedure. These systems are extensively characterized by thermoanalytical techniques (water uptake determination, HR-TGA, MDSC, DMA), vibrational spectroscopy (FT-IR ATR), SEM, HR-TEM, and broadband electric spectroscopy (BES). In general, the addition of nanofiller reduces the water uptake and improves the mechanical properties of the hybrid membranes as compared to pristine Nafion. Promising conductivities are obtained for the hybrid membranes at T=115°C (7.5x10-2 Scm-1 at 9wt% nanofiller vs. 3.3x10-2 Scm-1 for Nafion). The interplay between the structure and the proton conduction mechanism is investigated and reveals the presence of two electric polarizations associated with structural inhomogeneities of the materials. Finally, the best performing hybrid membrane (9 wt% nanofiller) is used to manufacture a membrane-electrode assembly (MEA) which is tested in single fuel cell configuration. The results demonstrate an improved fuel cell performance at low hydration levels in comparison with pristine recast Nafion.
3:00 PM - B11.2
Effect of Pretreatment on Morphology and Transport Properties of PFSA Membranes.
Ahmet Kusoglu 1 , Adam Weber 1
1 , Lawrence Berkeley National Laboratory, Berkeley, California, United States
Show AbstractIonomers are multi-functional, ion-conductive materials that are suitable for electrochemical devices for energy applications. Perfluorosulfonic-acid (PFSA) membranes in particular are commonly used as the base material for developing ion-conductive membranes, especially for polymer-electrolyte fuel cells (PEFCs). Transport properties of PFSA membranes, which are critical for the performance of PEFCs, strongly depend on the temperature and their water content. Also, the methods used for membrane preparation, such as as-received, drying at elevated temperature, or boiling in water, are known to alter the membrane's water content significantly. However, the effect of the membrane's thermal history on its transport properties and morphology has not been examined in detail in the literature. In this talk, we present our findings on the effect of pretreatment on the water content, morphology at the nanoscale, and ionic conductivity and transient water-uptake behavior of Nafion PFSA ionomer at different temperatures and humidities. The tests were conducted using membrane samples that are as-received (from the manufacturer), predried (at elevated temperatures) and preboiled (in water) prior to the measurements. Preboiling the membranes is found to increase the overall water uptake and conductivity compared to the predried and as-received membranes. In addition, we performed small-angle X-ray (SAXS) experiments to investigate the morphology of the swollen membranes as a function of humidity using samples with different pretreatment history. The SAXS data shows that the nanostucture of the membrane changes with pretreatment which affects the size of the water domains and the distance between the crystalline domains in the matrix. Our results indicate a strong correlation between the structure and properties of PFSA ionomers, and it is shown for the first time that this relationship and not just the absolute values depend on pretreatment method. Thus, pretreatment and thermal histories of ionomer membranes have important influence on membrane's transport and electrochemical properties and could potentially change the functionality of ionomers. The findings of this work can be helpful for exploring the methods to control the structure-property relationship of ionomers and for developing alternative materials for energy applications. AcknowledgementThis work was funded by the Assistant Secretary for Energy Efficiency and Renewable Energy, Office of Fuel Cell Technologies, of the U. S. Department of Energy under contract number DE-AC02-05CH11231.
3:15 PM - B11.3
New Insights into the Microstructure of PFSA Ionomers: A Cord Length Distribution Analysis (CLD) of Small-Angle X-Ray Scattering (SAXS) Data.
Simone Mascotto 1 , Klaus-Dieter Kreuer 2 , Giuseppe Portale 3 , Carla Cavalca de Araujo 2
1 Dipartimento di Ingegneria dei Materiali e Tecnologie Industriali, Università degli Studi di Trento, Trento Italy, 2 , Max-Planck Institut für Festkörperforschung, Stuttgart Germany, 3 DUBBLE BM26, ESRF, Grenoble France
Show AbstractThe unique properties of PFSA ionomers such as Nafion are generally considered to be closely related to their particular microstructure which is generally studies by small angle x-ray scattering. Since a straight forward interpretation of SAXS spectra is generally not possible (simply because they do not contain sufficient information), most approaches are making use of structural models (spherical, cylindrical, lamellae), which are not able to resolve unambiguously the nanostructure of the membrane, giving then too many different possible solutions.In the present work, Nafion and Hyflon SAXS curves are evaluated by means of a parametrization model based on basic analytical functions. This approach, called Chord Length Distribution (CLD), does not need structural models and is particularly appropriate to characterize the structure of two-phase systems like Nafion. This method does not provide the full structural information but certain aspects, such as the average size of the nanodomains, prevalent length scales, correlation lengths, and the specific interface area.In particular, the microstructure of the ionomers was studied by SAXS controlling different experimental condition (temperature, hydration level and aging). One of the most interesting results, by the application of the CLD, is that the water confined in the membrane is organized in domains of ca. 1 nm separated by “polymer walls” of ca. 2 nm. Furthermore, it was found that the exposition at elevated hydration levels increases the size and the distribution of the water domains, while the raise of temperature and time of aging shrinks the polymer nanostructure.
3:30 PM - B11.4
Elaboration of Nanostructured and Highly Proton Conductive Membranes for PEMFC by Ion Track Grafting Technique.
Enrico Gallino 1 , Marie-Claude Clochard 1 , Thomas Berthelot 2 , Emmanuel Balanzat 3 , Gerard Gebel 4 , Arnaud Morin 5
1 Laboratoire des Solides Irradiés, CEA Saclay-Ecole Polytechnique-CNRS, Palaiseau France, 2 SPCSI, CEA Saclay, Gif sur Yvette France, 3 CIMAP, CEA-CNRS-ENSICAEN, Caen France, 4 INAC-SPRAM, CEA Grenoble, Grenoble France, 5 LITEN-LCPEM, CEA Grenoble, Grenoble France
Show AbstractDespite some serious drawbacks (high cost, conductivity losses at high temperature, water swelling shortening the membrane durability), Nafion® is still the reference as membrane for PEMFC. In order to develop a new type of proton conductive membrane, our strategy is based on the utilization of swift heavy ions (SHI) grafting process to create nanometric cylindrical proton conductive pathways, in the thickness direction of the membrane, to enhance proton conduction from the anode to the cathode. The mechanical and dimensional stability of the proton exchange membrane was insured by the pristine PVDF matrix. In particular, a poly(vinyl di-fluoride) (PVDF) matrix was irradiated with SHI to obtain radically active latent tracks in the polymer film. Styrene was then radiografted and further sulfonated into these irradiated cylindrical regions, leading to sulfonated polystyrene (PVDF-g-PSSA) domains within PVDF. The role of the grafting degree and fluence of irradiation of the PVDF matrix on PVDF-g-PSSA membranes properties (chemical composition, ion exchange capacity, water uptake) was investigated. Then, a membrane-electrode assembly (MEA) was prepared and fuel cell tests have been performed. The cell temperature was progressively increased from 50°C to 80°C. Polarization curves and electrochemical impedance spectroscopy (EIS) at different current densities were used to evaluate the membrane-electrode assembly (MEA) performances.Our results clearly show that PVDF-g-PSSA membranes with a grafting degree of about 140% (PVDF-g-PSSA 140%), obtained after irradiation at a fluence of 1010 ions/cm2, lead to proton conductivities ranging from 30 mS/cm to 60 mS/cm depending on the operating conditions. These values are close to those of a Nafion® membrane tested in the same conditions. However, the durability of these membranes is limited to about 70 hours due to high stiffness of the membrane that weakens mechanical properties during fuel cell operation. To increase the durability, one solution was to decrease the fluence. The decrease of the fluence leads to membranes with lower grafting yield (about 45%). However, despite the lower grafting degree and the lower amount of sulfonated groups, fuel cell performances are similar to those of (PVDF-g-PSSA 140%) membrane. This result indicates that the cylindrical nanocomposite structure plays a key role in the enhancement of the proton conductivity. Moreover, the good fuel cell performances are associated to adequate mechanical properties that improve the durability of the membrane. In conclusion, our work demonstrates that SHI grafting is a powerful and low cost (about 200 US$/m2 of membrane) technique to obtain a specific and controlled nano-scale structure allowing a good trade-off between adequate mechanical stability and high proton conductivity.
3:45 PM - B11.5
Nano-Engineered Proton and Electron Conducting Materials for Fuel Cells Application.
Chau Tran 1 , Vibha Kalra 1
1 Chemical and Biological Engineer, Drexel University, Philadelphia, Pennsylvania, United States
Show AbstractWe report novel results on fabrication and characterization of hybrid nanofiber mats that conduct both electrons and protons simultaneously. The ultimate aim is to develop porous catalyst supports (for proton exchange membrane fuel cells) with well-defined triple phase boundary, necessary for efficient transport of electrons, protons and oxygen gas to the catalyst sites for the oxygen reduction reaction to take place at the cathode. Nanofibers have been fabricated using a process called electrospinning that uses strong electric field to thin a polymer solution or melt jet forming ultra thin fibers with diameters in the range of 50-500nm. As a first step, nanofibers of polyacrylonitrile (PAN)/Nafion blends have been fabricated over a wide range of compositions by varying PAN from 10% to 60 wt%. Fast evaporation of solvent (~200 nl/s) and high elongational flow rate (~105 s-1) during electrospinning allowed us to prevent phase separation and develop a co-continuous morphology of PAN and Nafion in the nanofibers. Nanofibers were microtomed into thin 60-80 nm sections and characterized using transmission electron microscopy (TEM) to confirm the internal morphology in nanofibers both along the fiber axis and perpendicular to the axis. In addition, preliminary measurements using impedance spectroscopy showed a sufficient proton conductivity of PAN/Nafion fiber mats, indicating the existence of a continuous percolating network of Nafion within the nanofibers (resulting in uninterrupted proton transport). As a second step, multi-walls carbon nanotubes (MWCNTs) have been incorporated in PAN/Nafion nanofibers to impart electron conductivity. Owing to the affinity of MWCNTs with PAN, these electron conducting nanotubes can be confined in the PAN phase to achieve percolation at a much smaller volume fraction. Smooth nanofibers with MWCNTs aligned along the fiber axis have been fabricated, which facilitates the formation of a percolating network of MWCNTs for efficient electron transport.In addition to developing multi-functional catalyst supports for fuel cells, nanofibers of PAN/Nafion blends have also been used to fabricate high surface area, uniformly porous nanofibers of pure carbon or pure Nafion by selective removal of Nafion (followed by high temperature treatment) or PAN respectively. While porous carbon nanofibers can have a wide range of applications including gas purification and catalyst support for batteries, high surface area porous Nafion nanofibers can be used to develop super-sensitive gas sensors.
4:00 PM - B11: PEM mem 2
BREAK
B12: PEM Materials II
Session Chairs
Wednesday PM, November 30, 2011
Constitution B (Sheraton)
4:30 PM - **B12.1
Novel Polymer Electrolyte Membrane Materials with Segmented Block and Comb Copolymer Architecture.
Michael Guiver 1 2 , Nanwen Li 1 , Chenyi Wang 1 , Young Moo Lee 1
1 ICPET, M-12, National Research Council Canada, Ottawa, Ontario, Canada, 2 WCU Department of Energy Engineering, Hanyang University, Seoul, 133-791, Korea (the Republic of)
Show AbstractAmong the challenges facing hydrocarbon-based (HC) PEMs is their tendency to swell excessively in a humidified environment, leading to a loss of mechanical integrity, as well the marked decrease in conductivity observed in a reduced-humidity environment that would be encountered when operating a fuel cell at elevated temperatures. In addition, since fuel cell membrane electrode assemblies are almost universally constructed using Nafion ionomer as a glue to bind the catalyst to the PEM, a dimensional mismatch and mechanical failure leading to electrode delamination occurs when there are significant differences in swelling behaviour between the interface. In order to design PEMs that maintain adequate conductivity in environments that range from fully humidified to 50% relative humidity, without excessive changes in dimensional stability, careful consideration must be given to design structural architecture that can induce phase separation.Our current research focuses on designing PEM architecture, which contains segmented structures with densely-spaced sulfonic acid groups in the conducting block, allowing self-organization of polymers into hydrophilic proton-conducting domains and hydrophobic domains. New types of blocky PEM architecture, which include segmented copolymers, wholly aromatic comb copolymer systems, and tri-blocks have been constructed, and the PEM properties of these are compared. Among these, wholly aromatic comb copolymer architecture has not previously been reported. Some of the PEMs exhibit unusually low dimensional swelling in the planar direction and good proton conductivity under partially hydrated conditions relative to other HC-PEMs.
5:00 PM - B12.2
Proton Dynamics in Pyridinium-Based Protic Ionic Liquids.
Jason Simmons 1 , Timothy Jenkins 1 , Jeffery Thomson 2 , Don Gervasio 3
1 , NIST Center for Neutron Research, Gaithersburg, Maryland, United States, 2 , Oak Ridge National Lab, Oak Ridge, Tennessee, United States, 3 , University of Arizona, Phoenix, Arizona, United States
Show AbstractIonic liquids have found widespread use in a number of applications, especially as electrolytes in electrochemical capacitors and PEM fuel cells. The protic ionic liquids (PILs), formed by mixing Brønsted acids and bases, are particularly interesting given their high ionic conductivities, wide temperature range of operation, and intrinsically anhydrous conduction. Ideally, PILs will be incorporated into polymer membranes to enable their application in fuel cells. Here we discuss the proton and hydrogen dynamics in a group of pyridinium-based PILs, both as free ionic species as well as covalently grafted onto a polymer backbone, with an eye to understanding their proton activity in electrochemical applications. Using quasielastic neutron scattering (QENS), we are able to differentiate between the different hydrogen dynamics in each PIL, motions which can consist of vehicular transport of molecular ions and internal vibrational and rotational dynamics in addition to proton conduction. We are able to extract both the energetics of each motion as well as the spatial extent of the motions such as hydrogen jump distances and diffusivities. The QENS measurements afford a picture of the detailed molecular mechanism underlying the hydrogen dynamics and ultimately inform upon the measured electrochemical proton conductivity.
5:15 PM - B12.3
Synthesis and Characterizations of Novel Non-Platinum N4 Macrocyclic Cobalt Catalyst for Fuel-Cell Application.
Indrajit Shown 1 , Kuei Hsien Chen 1 2 , Li-Chyong Lin Chen 2 , C. Wang 3 , S. Huang 2 , S. Chang 2 , Y. Fu 3 , Ken Wong 4
1 Institute of Atomic and Molecular Sciences (IAMS), Academia Sinica, Taipei Taiwan, 2 Center for Condensed Matter Sciences, National Taiwan University, Taipei Taiwan, 3 Department of Materials Science and Engineering, National Taiwan University of Science and Technology, Taipei Taiwan, 4 Department of Chemistry, National Taiwan University, Taipei Taiwan
Show AbstractPoor oxygen reduction reaction (ORR) kinetics and the increasing price with extremely rare earth Pt catalyst on fuel cell are the most limiting factors slowing the commercialization of fuel cell. Recently the developments of unconventional novel non-platinum catalysts including transition metal N4-macrocycles such as phthalocyanine and phorphyrin are known to catalyze oxygen reduction reaction. Using bio mimetic approach to synthesized new catalysts for energy conversion is one of the revolutionary dreams. One of the structures present in many enzymes is the corrinoid structure. N-4 macrocyclic chemistry has recently received a new propel and it has been shown to be a versatile ligand capable of coordinating transition metals without significant distortion of the macrocycle plane. The particular ligand behavior of corroles can be of interest for its catalytic application in redox reaction. The N-4 macrcocyclic compound acts as a trianionic ligand, different from both corrins and porphyrins, which are, respectively, monoanionic and dianionic ligands. Furthermore, the ability of corroles to stabilize higher oxidation states of the metal as compared to porphyrins makes its coordination chemistry particularly interesting. Metallo macrocyclic compounds are the potential active catalyst for the various transformations. In this study we synthesized Co(III)-N-4 macrocyclic complexes catalyst with moderate yield for oxygen reduction reaction in fuel cell application after pyrolyzed. The pyrolysis process of the synthesized catalyst will decrease the activation energy of the reaction and increases the catalytic efficiency of ORR in fuel cell. This is first time reported pyrolyzed Co(III)-N-4 macrocyclic as non platinum catalyst for fuel cell application. In PEMFC test the prepared catalyst gives a current density of 743 mA cm-2 with a maximum power density of 218 mW cm-2. Whereas TMPP(5,10,15,20 tetrakis (4-methoxyphenyl) porphyrin) shows a current density of 374 mA cm-2 with a maximum power density of 122 mW cm-2.
5:30 PM - B12.4
Novel Quaternary Catalyst with High Current Density for Direct Methanol Fuel Cell.
Aditi Halder 1 , Sanjeev Mukerjee 1
1 Chemistry and chemical biology, Northeastern University, Boston, Massachusetts, United States
Show Abstract The platinum-based electrocatalysts exhibit exclusively the requisite reactivity and stability in the acidic environment of Direct Methanol Fuel Cell. The state-of the art PtRu catalysts witnessed its own issues of dissolution of ruthenium and hence the anode catalysts with improved activity and durability is on constant demand. Here we report the development of two novel ternary and quaternary catalysts containing platinum, ruthenium, gold and lead. The core-shell ternary catalyst has PtRu as core and lead on the shell and the quaternary catalyst comprised of inner core of PtRu alloy surrounded by nano-shell lead and gold. Both the catalysts showed the higher current density than the commercial PtRu catalysts. The long term chronoamperometry carried out at 550 mV also showed good durability compared to commercial catalyst. Lead (Pb) had shown promoting effect on the electro-oxidation of alcohols and organic fuels and found to be resistant to CO poisoning. The controlled CO adsorption experiments carried out to evaluate the role of Pb in CO poisoning. The use of trace amount of gold improves the stability of both ruthenium and lead; hence imparts the extra stability of PtRu@PbAu/C catalysts. The electrochemical, microstructural and compositional studies have been investigated out for both the ternary and quaternary catalysts by Cu under-potential deposition (UPD), transmission electron microscopy (TEM), X-ray diffraction (XRD) and X-ray absorption spectroscopy (XAS) analysis. Electrochemical experiments and in-situ XAS analysis confirmed the role of lead and gold in the in the PtRu@Pb/C and PtRu@PbAu/C catalysts. The performances of these catalysts under fuel cell operating conditions have been carried out to estimate their power density and energy efficiency.
5:45 PM - B12.5
The Electrical and Corrosional Properties of Vinyl Ester Composite Coated on the Stainless Steel Bipolar Plate for PEM Fuel Cell.
Yang-Bok Lee 1 , Kyung-Min Kim 1 , Eun-Ji Hwang 1 , Dae-Soon Lim 1
1 Materials Science and Engineering, Korea University, Seoul Korea (the Republic of)
Show AbstractPolymer electrolyte membrane fuel cell (PEMFC) is a promising energy generation source for a home station and automobile. Bipolar plates are one of the most important components of a PEM fuel cell stack. Bipolar plates have many functions such as supporting of stack, distribution of air and fuel, and current collector of generated electrons. Therefore, bipolar plates need many requirements; high electrical conductivity, mechanical strength and corrosion resistance, low volume and weight, and low fabrication cost. For commercial use, stainless steel bipolar plate has developed alternative to commercial graphite bipolar plate. The stainless steel bipolar plates are high electrical conductivity and mechanical strength, and low fabrication cost. However, those need a conductive passivation coating owing to low corrosion resistance under PEM fuel cell operation condition. Therefore, corrosion is the main technical issue with the stainless steel bipolar plates. Many coating materials on the stainless steel bipolar plate have been developed, such as noble metals, carbon, ceramic, conducting polymer and polymer composites. Compared to other coating materials, a polymer composite coating can be formed easy on metal surfaces. However, high contact resistance was generated between composite layer and stainless steel. Previous reported paper shows that grown carbon nanotubes on the stainless steel improve the electrical property between composite layer and stainless steel plates. In this study, vinyl ester composite coated on the stainless steel bipolar plates were fabricated by painting method and investigated with electrical and corrosional properties. For improvement of electrical property, carbon nanotubes were grown on the stainless steel before the composite coating. Vinyl ester and carbon black were used as binder and conducting filler of composite, respectively. Optimum composition of carbon black and vinyl ester on the electrical and corrosional properties was tested. Also, optimum condition of carbon nanotube growth on the stainless steel was investigated for painting method.
B13: Poster Session III
Session Chairs
Maria Luisa Di Vona
Joshua Hertz
Philippe Knauth
Harry Tuller
Thursday AM, December 01, 2011
Exhibition Hall C (Hynes)
9:00 PM - B13.1
Phase Stability and Electronic Structure of LaMnO3: A Hybrid Density Functional Study of an Alkaline Fuel Cell Catalyst.
Ehsan Ahmad 1 2 , Denis Kramer 1 3 , Leandro Liborio 1 2 , Giuseppe Mallia 1 2 , Nicholas Harrison 1 2 4 , Anthony Kucernak 1
1 Department of Chemistry, Imperial College, London United Kingdom, 2 Thomas Young Centre, Imperial College, London United Kingdom, 3 Faculty of Engineering and the Environment, University of Southampton, Southampton United Kingdom, 4 , Daresbury Laboratory, Daresbury United Kingdom
Show AbstractThe phase stability and electronic structure of low temperature LaMnO3 are studied using hybrid-exchange density functional theory (DFT) in CRYSTAL09. The underpinning DFT total energy calculations are embedded in a thermodynamic framework that takes optimal advantage of error cancellation within DFT. It has been been found that by using the ab initio thermodynamic techniques described here, the standard Gibbs formation energies can be calculated to a significantly greater accuracy than was previously reported (a mean error of 1.6% with a maximum individual error of -3.0%). This is attributed to both the methodology for isolating the chemical potentials of the reference states, as well as the use of the B3LYP functional to thoroughly investigate the ground state energetics of the competing oxides. The electronic structure is investigated in terms of total and projected density of states.
9:00 PM - B13.10
Structurally-Tailored PtNiFe and PtNiCo Nanoparticles for Advanced Fuel Cell Catalysts.
Bridgid Wanjala 1 , Bin Fang 1 , Jin Luo 1 , Rameshwori Loukrakpam 1 , Jun Yin 1 , Chuan-Jian Zhong 1
1 Department of Chemistry, State University of New York at Binghamton, Binghamton, New York, United States
Show AbstractThe ability to control the activity and stability of multimetallic alloys is important for the design of advanced fuel cell catalysts. This presentation describes the results of an investigation of synthesis, characterization, and preparation of trimetallic PtNiFe and PtNiCo nanoparticle electrocatalysts with the aim of providing a new fundamental insight into the role of the detailed atomic alloying and interaction structures of the catalysts in fuel cell reactions. Important insights into the formation of surface oxides on the nanoparticle surfaces under different processing conditions were gained based on XAFS and XPS characterizations. The XAFS analysis of the atomic-scale coordination structures revealed increased hetero-atomic coordination with improved alloying structures for the catalyst treated at the elevated temperatures. XPS analysis further revealed a reduced surface concentration of Pt for the catalyst for the high temperature treated catalysts. The electrocatalytic activities and stabilities of these catalysts were examined for oxygen reduction reaction using rotating disk electrode and in PEMFCs. These catalysts were shown to exhibit enhanced electrocatalytic activity and stability and fuel cell performance. Implications of these findings to the design of highly active and durable alloy electrocatalysts in actual fuel cells are also discussed.
9:00 PM - B13.11
Electrodeposited Platinum and Nitrogen Cluster Functionalized Carbon Nanotube Sheet Electrodes in Hydrogen Fuel Cells.
Shao-Chun Hsu 1 , Shiunchin Wang 2 , Zafar Iqbal 1
1 Chemistry, New Jersey Institute of Technology, Newark, New Jersey, United States, 2 , CarboMet LLC, Newark, New Jersey, United States
Show AbstractSelf-assembled sheets of multiwall carbon nanotubes electrochemically decorated with Pt nanoparticles were used as the anode and cathode in a small (16 cm2 area bipolar plates and 10 cm2 area electrodes) hydrogen fuel cell with a Nafion membrane. The performance of this fuel cell was found to be comparable to that of a Nafion-membrane fuel cell of the same footprint using commercial electrodes comprising of Pt coated carbon black. When the Pt-coated carbon nanotube (CNT) anode or cathode is replaced by a CNT electrode comprised of electrochemically deposited metal-free nitrogen clusters from a nitrogen-rich precursor, the performance drops approximately by a factor of two. However, the overall power is still appreciable and is expected to be improved with further optimization of the nitrogen cluster functionalization of the CNT sheets. When a pristine CNT sheet is used as either the anode or cathode in a fuel cell with a commercial counter electrode, the fuel cell power drops to zero, thus confirming the catalytic activity of the novel nitrogen cluster@CNTs electrode. A possible mechanism for the catalytic activity of the nitrogen clusters@CNTs electrode and its comparison with that of a carbon nanotube-based enzymatic biofuel cell [1] will also be discussed.[1] “Membrane-less and Mediator-free Enzymatic Biofuel Cell using Carbon Nanotube/Porous Silicon Electrodes”, S.C. Wang, F. Yang, M.Silva, A. Zarow and Z. Iqbal, Electrochem. Commun. 11, 34 (2009).
9:00 PM - B13.12
Noble Metal Catalysts for Efficient Energy Utilization.
Feng Wang 1 2 , Ling-Dong Sun 1 , Jianfang Wang 2 , Chun-Hua Yan 1
1 Chemistry, Peking University, Beijing China, 2 Physics, The Chinese University of Hong Kong, Hong Kong Hong Kong
Show AbstractThe development of high-performance noble metal catalysts with large surface areas and high activities is a major concern in the chemical industry. Towards this goal, we have developed two routes to create high-performance noble metal catalysts. One is to grow high-index-faceted noble metal catalysts containing a high density of surface catalytic centers. Two types of Pd nanoshells are obtained by inheriting epitaxially the high-index {730} and {221} facets from two types of Au nanocrystal cores, respectively. The catalytic performances of these high-index-faceted Pd nanoshells for the Suzuki coupling reaction are measured to be 3-7 times those of Pd and Au-Pd core-shell nanocubes that possess only {100} facets. The other is to fabricate porous Pd single crystals exhibiting a large surface area. The catalytic performance of the porous Pd crystals is ~30 times that of commercial Pd on carbon using iodobenzene substrate, and is ~6 times using bromobenzene substrate. The porous crystals also have good substrate selectivity, favoring m-tolylboronic acid and m-bromoanisole. These results demonstrate that both high-index-faceted metal nanocrystals and porous metal crystals are excellent nanocatalytic systems for organic reactions and surface chemical processes, allowing us to push the envelope in the development of more efficient and stable catalysts for the petroleum industry.
9:00 PM - B13.13
Advanced Pt-Bimetallic Alloy Electrocatalysts.
Chao Wang 1 , Nenad Markovic 1 , Vojislav Stamenkovic 1
1 Materials Science Division, Argonne Nat Lab, Argonne, Illinois, United States
Show AbstractAlloying has shown enormous potential for tailoring the atomic and electronic structures, and improving the performance of catalytic materials. However, the quality of alloy materials, in terms of key parameters such as particle size, alloy composition and homogeneity, surface structure and element profile, can compromise the study for alloy catalysts. Here I present our organic solution approach toward monodispersed and homogeneous Pt-bimetallic alloy (Pt3M, where M = Fe, Ni or Co) nanocatalysts and their catalytic applications for electrocatalytic reduction of oxygen. Pt3M nanoparticles were prepared by simultaneous reduction of platinum and 3d transition metal salts, or coupling the reduction of platinum salts with the thermal decomposition of metal carbonyls, in an organic solution. The obtained alloy NPs were then supported on carbon with the organic surfactants removed by thermal treatment. Based on these high-quality alloy nanocatalysts, we investigated the dependence of electrocatalytic activity on particle size, alloy composition, surface structure, as well as pretreating conditions. We found that the nanoscale architecture for Pt-bimetallic catalyst could be optimized to possess a Pt0.5Ni0.5 core with a multilayered Pt-skin surface, which exhibited enhanced catalytic activity for the oxygen reduction reaction (ORR) with an improvement factor of 6 versus conventional Pt/carbon catalysts. Durability studies under potential cycling in combination with in situ X-ray absorption spectroscopy (XAS) analysis further demonstrated the obtained Pt-bimetallic catalyst with multilayered Pt-skin surface is stable under the reaction conditions, achieving enhancement of more than one order of magnitude in mass activity versus Pt/carbon after elongated potential cycling. Our work represents a persuasive approach towards comprehensive understanding of structure-property correlation at nanoscale, and it could be generalized to the development of other advanced functional nanomaterials.
9:00 PM - B13.14
Generating Electricity from Biofluid with a Nanowire-Based Biofuel Cell for Self-Powered Nanodevices.
Caofeng Pan 1 2 , Zhonglin Wang 1 , Jing Zhu 2
1 Materials Science and Engineering, Georgia Institute of Technology, Atlanta, Georgia, United States, 2 Materials Science and Engineering, Tsinghua University, Beijing China
Show AbstractHarvesting chemical energy in biofluid can be a powerful approach for fabricating sustainable, independent, mobile and self-powered nanodevices for in-vivo biosensing. We report the nanowire-based biofuel cell (NBFC) based on a single proton conductive polymer nanowire (NW) for converting chemical energy from biofluid such as glucose/blood into electricity, with glucose oxidase (GOx) and laccase as catalyst. The glucose is supplied by biofluid, the NW serves as the proton conductor, and the whole cell is accomplished at nano/micron scale. The NBFC of a single NW generates an output power as high as 0.5-3 μW, and it has been integrated with a set of nanowire based sensors for performing self-powered sensing. This study shows the feasibility of building self-powered nanodevices for biological sciences, environmental monitoring, defense technology and even personal electronics. (Pan, C. F.; et al, Generating Electricity from Biofluid with a Nanowire-Based Biofuel Cell for Self-Powered Nanodevices. Adv. Mater. 2010, 22 (47), 5388)
9:00 PM - B13.15
Face to Face with Enemy – Second Surface Phases in Perovskite Ceramic Electrolytic Membrane.
Aneta Slodczyk 1 , Caroline Tran 1 , Philippe Colomban 1
1 , LADIR CNRS UPMC, Paris France
Show AbstractThe various perovskite ceramic electrolytic membranes, (Ba,Sr)(Zr,Ce,Nb,In,Sn)O3 modified by incorporation of Ln/RE elements, are widely investigated due to their high industrial potential for H2/CO2 production/conversion [1,2]. One of the most important criteria to classify such a ceramic as good membrane is its high mechanical and chemical stability over thousands hours in severe operating conditions: high temperature and high water vapour pressure cycling. It is well known that the Ba and Sr – based materials can easily form the carbonates, hydroxides, hydrates, hydrooxycarbonates, … The presence of such second, undesirable phases, even limited to traces, on the ceramic surface and/or at the grain boundary may lead directly to the premature efficiency loss [3]. It should be stressed that the low crystalline (hydrated) phases can be not detected at diffraction experiments, so the standard sample controlling by X-ray diffraction is not sufficient. Much better results are obtained using the combination of vibrational spectroscopy (Raman and IR) and thermogravimetric analysis. One should however know well their spectroscopic signatures especially that they are complex and often misinterpreted as signal of successful protonation [4]. Consequently, we have performed the IR and Raman study in a wide wavenumber range of potential second phases: in raw state, deuterated and treated under acid and basic atmospheres. The assignment of observed signatures is proposed. The vibrational and TGA results reveal complex character of the investigated second phases, i.e. (Sr, Ba)(OH)x(CO3)y,nH2O.1. G. Olah, Angew. Chem. Int. Ed. 2005 44 26362. Ph. Colomban Ed. Proton Conductors, Cambridge University Press, Cambridge (1992) 3. A. Slodczyk et al. MRS Proceedings. 1311 (2011) mrsf10-1311-gg06-25. doi: 10.1557/opl.2011.1074. A. Slodczyk et al. MRS Proceedings 1309 (2011) mrsf10-1309-ee03-21. doi: 10.1557/opl.2011.616
9:00 PM - B13.16
Formation of an Epitaxial Brownmillerite Phase Material in Manganate Heterostructures.
John Ferguson 1 2 , Yongsam Kim 3 , Lena Fitting Kourkoutis 3 , Aaron Vodnick 1 , Arthur Woll 4 , David Muller 3 , Joel Brock 3
1 Department of Materials Science and Engineering, Cornell University, ithaca, New York, United States, 2 , Massachusetts Institute of Technology Lincoln Laboratory, lexington, Massachusetts, United States, 3 School of Applied and Engineering Physics, cornell university, Ithaca, New York, United States, 4 Cornell High Energy Synchrotron Source, Cornell University, ithaca, New York, United States
Show AbstractWe report the discovery of and subsequent investigations into the spontaneous formation of highly ordered (pseudomorphic) epitaxial layers of a novel crystal phase in manganate materials. The phase forms during the widely used (standard) procedure to create heterostructures of the well-known CMR material (La,Sr)MnO3 (LSMO). This discovery was enabled by the use of in-situ x-ray scattering, and since the phase transformation occurs at a buried layer, it is not detectable by conventional RHEED. The phase is oxygen deficient LSMO, where oxygen vacancies order into rows, and is described by the brownmillerite family of crystal structure. Due to their large oxygen mobility, brownmillerite phase materials are widely believed to be promising candidates for cathodes in solid oxide fuel cells. Indeed, LSMO cathodes are currently the industry standard. Thus, we have discovered that highly ordered heterostructures of a novel and technologically relevant materials are formed during the standard deposition procedures used to grow various types of complex oxide heterostructures.
9:00 PM - B13.17
Evaluation of GDC Interlayer for IT-SOFCs with BSCFZ-LSCF Composite Cathode.
Doh Won Jung 1 , Kyoung-Seok Moon 1 , Sooyeon Seo 1 , Chan Kawk 1 , Hee Jung Park 1
1 , Samsung Advanced Institute of Technology, Gyeonggi-do Korea (the Republic of)
Show AbstractCurrently, significant efforts have been devoted to the development of intermediate temperature solid oxide fuel cells (600-800oC; IT-SOFCs) for low cost and the long term stability. Mixed ionic-electronic conductor is widely used as the cathode material to replace the traditional La1-xSrxMnO3-δ (LSM) cathode for IT-SOFCs. We found that BSCFZ-LSCF composite cathode is superior to pure BSCF cathode. Anode-supported SOFCs with BSCFZ-LSCF composite cathode were fabricated using GDC interlayer on ScSZ electrolyte. The GDC interlayer is inserted between the composite cathode and ScSZ electrolyte to prevent formation of insulting phases. However, the reaction between GDC and ScSZ could deteriorate cell performance forming the layer of (Zr,Ce)O2-based solid solutions. This result demonstrates that the sintering temperature of GDC should be optimized to suppress the reaction between cathode and zirconia electrolyte as well as minimize the (Zr,Ce)O2-based solid solution. In this study, the effect of GDC interlayer as a function of sintering temperature on cell performance, the thickness of (Zr, Ce)O2-based solid solution and Sr diffusion was investigated.
9:00 PM - B13.18
Synthesis and Ionic Conductivity of Sm0.1-xNdxCe0.9O2-δ Co-doped Ceria Electrolytes.
Robert Kasse 1 , Luping Li 1 , Juan Nino 1
1 Materials Science and Engineering, University of Florida, Gainesville, Florida, United States
Show AbstractCo-doping ceria with rare earth oxides has been shown to enhance ionic conductivity to values greater than those of singly doped materials. Density functional theory calculations have shown that a dopant with an atomic number near that of Pm+3 (61) could yield the lowest activation energy and thus highest ionic conductivity. Since Pm+3 is radioactive and unsuitable for use in fuel cell and other applications, our recent work using a co-doping scheme with Sm+3 (62) and Nd+3 (60) has shown that 1:1 co-doping results in conductivity values intermediate between the respective singly doped samples, with Nd-doped ceria showing higher ionic conductivities than Sm- or Gd-doped ceria. Here we present the expansion of the previous work to include non 1:1 co-doping in the Sm0.1-xNdxCe0.9O2-δ system. Samples were prepared using conventional solid state reactions and conductivity measurements were done using a two point probe ac electrochemical impedance spectroscopy technique from 250°C to 700°C in air. Activation energies were calculated from Arrhenius plots and were found to increase as dopants shifted from pure Sm+3 to pure Nd+3 in agreement with previous studies. More importantly, Sm0.075Nd0.025Ce0.9O2-δ showed a grain ionic conductivity of 0.0237±0.0004 S.cm-1 at 600°C which is the highest ever reported for either singly or co-doped ceria compositions.
9:00 PM - B13.19
Study on the Performance of Rapidly Quenched YSZ Electrolytes in Solid Oxide Fuel Cells.
Mirela Dragan 1 , Justin Roller 1 , Peter Strutt 2 , Radenka Maric 1
1 Center for Clean Energy Engineering, University of Connecticut, Storrs, Connecticut, United States, 2 , NanoCell Systems Inc, Mansfield Center, Connecticut, United States
Show AbstractSolid Oxide Fuel Cells (SOFCs) are being actively studied as viable alternatives for clean and efficient power generation using a variety of fuels and for use in portable devices. Research focus has been directed at decreasing the system cost by lowering the operating temperature of the fuel cells.Yttria stabilized zirconia (YSZ) has widely been used as an electrolyte in solid oxide fuel cell (SOFC) stacks. The microstructure and properties of rapidly quenched YSZ as a function of the fabrication process are discussed in this work. A series of 8 mol.% YSZ (8-YSZ) powders were manufactured by three different synthesis techniques: plasma sprayed using the Solution Precursor Plasma Spray technique (SPPS), Reactive Spray Deposition Technology (RSDT)techniques, and a wet technique.It is hypothesized that production of metastable nanostructured powders using a pyrolytic melting or vaporization of an aerosol-solution precursor in a DC-arc plasma, followed by rapid quenching produces nanoceramic and nanocomposite materials with a degree of homogeneity not otherwise attainable. The surface chemistry and structure of rapidly quenched (water quenched in this work) YSZ influences oxygen ion transport during the operation SOFCs at temperature smaller than 600°C. The ionic conductivity of YSZ depends strongly on both crystal structure and phase transformation. Therefore, prior to investigating the transport properties of the material, the evolution of the crystal structure and phase transformation was explored. Additionally the powders were characterized by SEM, TGA/DSC and finally XRD patterns were collected. Preliminary findings will be presented by comparing the physical and electrical properties of rapidly quenched YSZ nanopowders prepared by these manufacturing techniques.
9:00 PM - B13.20
Redox Stable Solid Oxide Fuel Cell with Ni–YSZ Cermet Anodes.
Aligul Buyukaksoy 1 , Vladimir Petrovsky 1 , Fatih Dogan 1
1 Materials Science and Engineering, Missouri University of Science and Technology, Rolla, Missouri, United States
Show AbstractReduction-oxidation (redox) stability of anode is crucial issue for solid oxide fuel cells (SOFC). It is known that redox cycling completely destroys co-sintered Ni-YSZ cermet in anode supported SOFCs and causes severe degradation in electrolyte supported SOFCs. Redox stable mixed oxide anodes have insufficient catalytic activity resulting in poor performance of the cells. Polymeric precursor infiltration technique has potential to solve this problem by introducing NiO polymeric precursor into a sintered porous YSZ layer. Electrolyte supported SOFCs were prepared with standard LSM-YSZ cathode and anode by infiltration technique. A porous YSZ layer was deposited on anode side of electrolyte and sintered at 1200°C. LSM-YSZ cathode layer was screen printed on cathode side of electrolyte followed by sintering at 1150°C. Anode cermet was fabricated by multiple infiltration of polymeric NiO precursor into porous YSZ layer and heat treated at ~400°C. Pt ink was used to form current collectors on both anode and cathode sides. Multiple reduction-oxidation of anode was accomplished by switching anode atmosphere between fuel (forming gas) and air at 800°C. Redox stability was characterized in situ by measuring short circuit current during switchings. Current - voltage and impedance spectroscopy measurements before and after redox cycles were conducted for detailed investigation of redox stability and long term performance of SOFCs. Cells showed acceptable performance (power density 0.3-0.4 W.cm-2 at electrolyte thickness ~200μm and operational temperature of 800°C), high redox stability (power density changed from 0.313 W.cm-2 in initial state to 0.311 W.cm-2 after 15 redox cycles), and good long term performance. Higher power densities can be achieved by simply decreasing the electrolyte thickness, which was dominating factor in the total cell resistance. Reported results confirm possibility of developing redox stable anodes for highly efficient SOFCs by utilizing polymeric precursor infiltration technique for Ni-YSZ anode deposition.
9:00 PM - B13.21
High Temperature Reduced Ni Substituted Titanates as New Hydrogen Electrode Materials for Solid Oxide Cells (SOCs) Showing Ni Nanoparticles Precipitation.
Charline Arrive 1 2 , Thibaud Delahaye 2 3 , Maria Teresa Caldes 1 , Gilles Gauthier 4 , Etienne Bouyer 2 , Olivier Joubert 1
1 , CNRS-IMN, Nantes France, 2 , CEA-LITEN, Grenoble France, 3 , CEA-LEMA, Marcoule France, 4 , UIS-Santander, Bucaramanga Colombia
Show AbstractLa substituted SrTiO3 are promising candidates for hydrogen electrode to replace the classical Ni/YSZ cermet. However, although they present high electrical conductivity and good stability upon redox cycling, their electro-catalytical activity is too low [1]. In this study, Ni-substituted titanates LaxSr1-xTi1-yNiyO3 (LSTN) are proposed as new hydrogen electrode materials for SOCs. In air, LSTN are single phase materials, whereas they are partially reduced under reducing atmosphere and in temperature, leading to precipitation of Ni nanoparticles on the oxide grain surface. This method, called exsolution, has been successfully applied to new hydrogen electrode material to enhance the performance of lanthanum chromites via Ni substitution [2]. In our case, electro-catalytical activity is thought to be improved by the Ni nanoparticles formed on the LSTN basic and electron conducting substrate [3].LSTN compounds were synthesized via sol-gel route. X ray diffraction data have been used to check the purity and to obtain the cell parameters. Reduction behaviour of LSTN compounds was studied through thermogravimetric analysis in Ar/H2 (2%). In situ reduction (at 800°C) and reduction treatments at temperature higher than 1000°C were performed and coupled with XRD analysis of the reduced powders. In both cases, TEM observations confirmed the presence of Ni nanoparticles. Conditions of the high temperature reduction treatment were thus optimized to have Ni exsolution without phase decomposition. Total conductivities of LSTN compounds, measured by 4-probe DC method in reducing atmosphere, is systematically higher after the high temperature reduction treatment. This behaviour is related to the formation of ε Ti3+, which is confirmed by magnetic susceptibility measurements. Besides, conductivity of the high temperature reduced phase measured during 500h at 800°C under Ar/H2 (2%)/H2O(3%) remains stable. Electrode polarisation resistances were evaluated by electrochemical impedance spectroscopy on symmetrical cells based on YSZ electrolyte. For optimized cells, they reach about 0.5 Ω.cm2 at 800°C under H2/H2O(3%) and are not affected by a re-oxidation treatment. [1] O.A. Marina et al. Solid State Ionics, 149 (2002) 21-28 [2] T. Jardiel et al. Solid State Ionics 181 (2010) 894–901 [3] T. Delahaye and G. Gauthier, French Patent N° 08 02032, (2008).
9:00 PM - B13.22
Optimization of Alloy-Coating Compositions for Use as Solid Oxide Fuel Cell Interconnects.
Jeffrey Fergus 1 , Yu Zhao 1 , Yingjia Liu 1
1 Materials Research and Education Center, Auburn University, Auburn, Alabama, United States
Show AbstractThe high operating temperature of solid oxide fuel cells (SOFCs) allows for the use of a variety of fuels, such as natural gas, reformed diesel fuel and biogas, which expands the range of potential SOFC applications. However, the high operating temperature can also lead to materials degradation. One important example of degradation in SOFCs is poisoning of the cathode from chromium deposits as a result of chromium volatilization from the stainless steel interconnect. The volatilization can be reduced through alloy design by the addition of manganese, which leads to the formation of a manganese chromium oxide spinel phase on the scale surface. However, additional reduction in volatilization is needed for long lifetimes, so ceramic coatings are applied to reduce chromium volatilization. One promising coating material is a manganese cobalt spinel oxide, which has high electrical conductivity and a coefficient of thermal expansion that is similar to other SOFC coating materials. After high-temperature exposure, the coating material reacts with the oxidation scale formed on the stainless steel alloy. The thickness of the resulting multilayer scale-coating combination increases with time, but the growth mechanism is different from that of the scale on uncoated alloy. Thus, the optimal composition of a coated alloy may be different than that of an uncoated alloy. Similarly, the optimal coating composition depends not only on the properties of the coating material, but also on those of the reaction layer formed between the coating and the alloy.In this paper, the interaction between interconnect alloys and ceramic coatings for use as SOFC interconnects will be discussed. The interaction layer generally contains regions with low electrical conductivity, so the electrical resistance of the reaction layer affects, and can even dominate, the area specific resistance of the cell. Thus, optimization of the alloy and coating compositions must take into account the composition and growth rate of the reaction layer formed between the alloy and coating. In this paper, the trade-offs in the design of alloy-coating combinations for use in SOFC interconnects will be discussed.
9:00 PM - B13.23
Solid Oxide Fuel Cell Performance with Mn1.5Co1.5O4 and LSCM Coated Haynes 230 Interconnect.
Lei Chen 1 , Ellen Sun 1 , Neal Magdefrau 1 , Jean Yamanis 1
1 Physical Sciences, United Tech. Research Center, East Hartford, Connecticut, United States
Show AbstractSolid oxide fuel cells (SOFC) with Mn1.5Co1.5O4 (MCO) and LSCM coated cathode interconnect (Haynes 230 (H230)) were tested at 750 °C. Despite significant difference in conductivity of the two coatings, the electrochemical performance of associated modules was identical. Strontium was detected at the MCO coating/H230 interface, likely in the form of SrCrO4. The Sr compound appears to preferentially form in ca. 1/2 of the curvature surface of a H230 interconnect wire. Such an enrichment of Sr apparently mimics the current distribution that is expected to minimize the ohmic loss due to electronic current flow in the cathode. It is postulated that electrical current might have enhanced the transport of Sr to interfacial reaction sites from the contact paste LSCF; however, the less conductive SrCrO4 did not seem to debit the performance of the cell, nor the short-term durability evaluated.
9:00 PM - B13.24
Fabrication of Enzyme - Nanotube Ensemble Films for High Power Biofuel Cells.
Syuhei Yoshino 1 , Keigo Haneda 1 , Takuya Ofuji 1 , Takeo Miyake 1 3 , Takeo Yamada 2 , Kenji Hata 2 , Matsuhiko Nishizawa 1 3
1 Bioengineering and Robotics, Tohoku University, Sendai Japan, 3 Core Research for Evolutional Science and Technology (CREST), Japan Science and Technology Agency (JST), Tokyo Japan, 2 Nanotube Research Center, National Institute of Advanced Industrial Science and Technology (AIST), Tsukuba Japan
Show AbstractNanostructured carbons have been widely used for fabricating enzyme-modified electrodes due to their large specific surface area. However, because they are random aggregates of particular or tubular nanocarbons, the postmodification of enzymes to their intrananospace is generally hard to control. Here, we describe a free-standing film of carbon nanotube forest (CNTF) that can form a hybrid ensemble with enzymes through liquid-induced shrinkage. This provides in situ regulation of its intrananospace (inter-CNT pitch) to the size of enzymes and eventually serves as a highly active electrode. The CNTF ensemble with fructose dehydrogenase (FDH) showed the oxidation current density of 16 mA cm−2 in stirred 200 mM fructose solution. The power density of a biofuel cell using the FDH−CNTF anode and the Laccase−CNTF cathode reached 1.8 mW cm−2 (at 0.45 V) in the stirred oxygenic fructose solution, more than 80% of which could be maintained after continuous operation for 24 h. Application of the free-standing, flexible character of the enzyme−CNTF ensemble electrodes is demonstrated via their use in the patch or wound form.In the presentation, we will report the condition and experimental result in detail.
9:00 PM - B13.25
Finite Element Modeling of Creep in High Relative Density Fe-26Cr-1Mo Foams.
Justin Scott 1 , David Dunand 2
1 , IDA Science and Technology Policy Institute, Washington, District of Columbia, United States, 2 Materials Science and Engineering, Northwestern University, Evanston, Illinois, United States
Show AbstractRecently, there has been significant interest in metallic foams for solid-oxide fuel cell (SOFC) interconnects where operating temperatures can reach up to 900 °C [1]. In this application, chromia-forming, Fe-based alloys are considered one of the best candidate alloy families due to their long term oxidation resistance, low resistivity, and coefficient of thermal expansion match with other stack materials. Nonetheless, long operating lifetimes (>10,000 hours) can lead to creep deformation while in service as a result of internal stresses (e.g., from residual or thermal mismatch in stationary applications) or external forces (e.g. from vibrations and impact in transportation applications). This creep response may be affected by the presence of a thin oxide layer (< 1 µm), which can lead to increased creep resistance from the reinforcing strength of the oxide [2]. To better understand the high temperature creep behavior of metallic foams, finite element models with three-dimensional, periodic unit cells were examined. A unit cell with a tetrakaidecahedron shape was created to closely match the angular, open cell geometry of a porous metal created by space-holder replication. Parametric creep studies were performed at a constant temperature of 800 °C with respect to stress (2-10 MPa), relative density (0.5 and 0.6), and oxide thickness (0 µm, 0.3 µm, and 0.9 µm). Calculated creep rates for the porous model were compared to published data on the creep of replicated E-Brite (Fe-26Cr-1Mo, wt.%) foams with relative densities of 49 and 57% at a temperature of 800°C. Qualitative agreement was found with models for bare (non-oxidized) E-Brite foams. For oxidized foams with a continuous 0-0.9 um thick oxide layer covering the interconnected pores, simulations captured the experimentally observed decrease in creep strain rates with increasing oxide thickness. Furthermore, an examination of the volume average matrix stress confirmed that the elastic, creep-resistant ceramic oxide layer reinforces the foam matrix via load transfer.[1] M.C. Tucker, Journal of Power Sources 195 (2010) 4570-4582.[2] J.A. Scott, D.C. Dunand, Acta Materialia 58 (2010) 6125-6133.
9:00 PM - B13.3
Kinetics Study of Carbon Supported Pd-Sn Electrocatalysts for the Ethanol Oxidation Fuel Cell Reaction in Alkaline Medium.
Xiaowei Teng 1
1 Chemcial Engineering, University of New Hampshire, Durham, New Hampshire, United States
Show AbstractEthanol powered direct alcohol fuel cells (DAFCs) have attracted a great attention recently as potential power sources due to higher energy density than hydrogen and methanol. Research efforts have been devoted to improving the electrocatalytic performance of Pd towards ethanol oxidation in alkaline media. Here we reported the synthesis of carbon supported Pd-Sn catalysts. Aberration–corrected scanning transmission electron microscopy (STEM) equipped with electron energy loss spectroscopy (EELS), X–ray diffraction (XRD) and X–ray photoelectron spectroscopy (XPS) are used to identify the heterogeneous structures of various Pd-Sn/C catalysts. The catalytic activity towards ethanol electro-oxidation in alkaline medium was studied by cyclic voltammetry, Tafel, and chronoamperometry. Pd-Sn/C displayed better electrocatalytic activity and stability towards poisoning than commercial Pd/C (E-TEK). The current density obtained for the electro-oxidation was affected by varying ethanol concentrations between 0.05 and 2 M, and the calculated reaction order for ethanol was 0.64. Both electrochemical measurements and density functional theory (DFT) calculations demonstrate that the superior electro-activity of Pd-Sn/C is directly related to the existence of non-alloyed SnO2 on surface. Our cross–disciplinary work, from wet chemistry synthesis of Pd–Sn catalysts, theoretical simulations, catalytic measurements, to the characterizations of “real” heterogeneous via complementary techniques, will highlight the intriguing structure-property correlations in nanosized catalysts, and have a transformative impact on the commercialization of DEFC technology by replacing Pt with low cost, highly active Pd-based catalysts.
9:00 PM - B13.4
Enhanced Oxygen Reduction Reaction Activity of PdPt Alloy Nanoparticles Catalysts with Pt-Enriched Surface.
Licheng Liu 1 , Shin-ichi Nagamatsu 1 , Gabor Samjeske 1 , Yasuhiro Iwasawa 1
1 Innovation Research Center for Fuel Cells, The University of Electro-Communications, Tokyo Japan
Show Abstract Slow rate of the cathodic oxygen reduction reaction (ORR) and high cost of Pt catalysts are the main restrictions to be improved in the PEFC application to automobiles. Many Pt alloys with transition metals, such as Fe, Co, Ni, Cu, etc. showed high activity for ORR but faced serious stability problem in acidic electrolytes. The Pd-Pt bimetallic catalysts turn out to be promising candidates for replacing Pt catalysts. Recent studies on Pd-Pt catalysts demonstrated the enhancement of ORR activity by shape and morphology control synthesis. But there is still problem in practical application partially due to the difficulty of production of such nanoparticles in a large scale. Here, we report the preparation and high ORR activity of PdPt nanoparticle catalysts with Pt-enriched surface by the simple co-reduction and sequential reduction methods. The NPs were firstly synthesized by polyol reduction followed by precipitation and washing. Then, the NPs were dispersed in ethanol and mixed with a given amount of Vulcan XC-72 carbon. After ultrasonic dispersion under stirring and collecting by centrifuge, the catalyst was treated under 20%O2/N2 gas flow at 200oC for 2h. The composition of bimetallic NPs was Pd:Pt=1 or 4 in a molar ratio. The catalysts are denoted as PdPt, Pt@Pd and Pd@Pt, respectively, in Table 1. The ORR mass activity based on Pt of various catalysts decreased in an order of 4Pd@Pt > Pd@Pt > PdPt >Pt > Pt@Pd > Pd. The catalysts were characterized by CV, CO-IR and XRD. The results are summarized in Table 1. The bulk crystal structure can be derived from the XRD patterns, while the surface properties are shown in CV and CO-IR peaks. Table 1 taken together reveals the structure of bimetallic Pt-Pd NPs as follows. The PdPt NPs prepared by co-reduction and Pd@Pt and 4Pd@Pt NPs are PdPt alloys with Pt-enriched surface. However, the structure of Pt@Pd NPs has a little complexity, which is composed of Pt-core and PdPt alloy-shell with a Pd enriched surface. In conclusion, the sequential reduction, firstly Pd reduction and second Pt reduction can produce PdPt alloy NPs with Pt surface enrichment. It is similar to PdPt NPs by co-reduction. The Pt surface enrichment in these samples is important for the high ORR activity.
9:00 PM - B13.6
Proton Conduction Promoted by 1H-1,2,3-benzotriazole in Non-Humidified Polymer Membranes.
Sevim Uenueguer Celik 1 , Ayhan Bozkurt 1
1 Chemistry, Fatih University, Istanbul Turkey
Show AbstractHeterocyclic protogenic solvents are promising candidates in production of proton conductive nonhumidifiedmembranes. In this work, 1H-1,2,3-Benzotriazole, BTri which is a novel protogenic solventwas incorporated into Nafion and polyvinylphosphonic acid, PVPA to produce novel anhydrous membranes.The composite membranes were characterized using FTIR, TGA and DSC. TGA results confirmedthe thermal stability of the membranes and DSC results verified the homogeneity of the materials. The protonconductivity of these polymer electrolyte membranes with respect to BTri content was investigated.1H-1,2,3-Benzotriazole promoted the proton conductivity of the membranes reaching approximately10−3 S/cm at 150 oC, under anhydrous conditions. Cyclic voltammetry (CV) results demonstrated that1H-1,2,3-benzotriazole has broad electrochemical stability domain.
9:00 PM - B13.7
Shape and Composition Controlled Electrocatalysts of Platinum Alloy Nanoparticles.
Jianbo Wu 1 , Rajinder Singh 1 , Adam Gross 1 , Hong Yang 1
1 Chemical Engineering, University of Rochester, Rochester, New York, United States
Show AbstractShape-controlled metal alloy nanocrystals have been the subject of active research as highly active catalysts in fuel cell, battery, and other chemical conversion systems. Since each crystallographic plane provides different surface atomic and electronic structures [1-2], the morphology of the catalyst can affect the activities greatly [3-5]. Thus, the design of faceted platinum alloy nanoparticles is critical for electrocatalytic application. Recently, we reported the use of gas reducing agent in liquid solution (GRAILS) approach to the preparation of a range of well-defined Pt alloy nanocrystals using a general reduction protocol [5]. Both {100} faceted cube and {111} faceted octahedron of Pt-Ni alloys have been produced. Besides, shape controlled nanocrystals of a broad composition range have been obtained under the same reducing reaction conditions with CO as the reductant. The facet-dependent Pt3Ni electrocatalysts show very high oxygen reduction reaction (ORR). In this presentation, I will discuss the structural factors that affect the facet formation of Pt-containing nanocatalysts using CO gas. Very high ORR mass activities of new facet-dependent catalysts have been observed and will be presented in this talk. References:[1] Stamenkovic, V. R.; Fowler, B.; Mun, B. S.; Wang, G. F.; Ross, P. N.; Lucas, C. A.; Markovic, N. M., Improved oxygen reduction activity on Pt3Ni(111) via increased surface site availability, Science 2007, 315, 493-497.[2] Stamenkovic, V. R.; Mun, B. S.; Arenz, M.; Mayrhofer, K. J. J.; Lucas, C. A.; Wang, G. F.; Ross, P. N.; Markovic, N. M., Trends in electrocatalysis on extended and nanoscale Pt-bimetallic alloy surfaces, Nat. Mater. 2007, 6, 241-247.[3] Wu, J.; Zhang, J.; Peng, Z.; Yang, S.; Wagner, F. T.; Yang, H., Truncated octahedral Pt3Ni oxygen reduction reaction electrocatalysts, J. Am. Chem. Soc. 2010, 132, 4984–4985.[4] Peng, Z. M.; You, H. J.; Wu, J. B.; Yang, H., Electrochemical Synthesis and Catalytic Property of Sub-10 nm Platinum Cubic Nanoboxes, Nano Lett. 2010, 10, 1492-1496.[5] Wu, J.; Gross, A.; Yang, H., Shape and Composition-Controlled Platinum Alloy Nanocrystals Using Carbon Monoxide as Reducing Agent, Nano Lett. 2011, 11, 798-802.
9:00 PM - B13.8
Relation of Mechanical Properties of Proton-Conducting Polymers with Macromolecular Structure, Additives and Thermal Treatments.
Mustapha Khadhraoui 1 , Philippe Knauth 1 , Jean-Francois Chailan 2 , M. Luisa Di Vona 3
1 LCP-MADIREL, University of Provence, Marseille France, 2 MAPIEM, University of Toulon, Toulon France, 3 Dip. Sc. Tecn. Chim., University of Rome Tor Vergata, Rome Italy
Show AbstractProton Conducting Polymers (SAPs) attract attention as possible electrolytes for Proton Exchange Membrane Fuel Cells. Objective of current development is to obtain a suitable proton-conducting polymer for use at intermediate temperatures (typically 120°C) and under low relative humidity and to improve long-term durability.Mechanical properties are fundamental for durability under fuel cell conditions. We have recently investigated polymer membrane characteristics by tensile tests and Dynamic Mechanical Analysis. [1-4]In this presentation, we will discuss the influence of materials composition, manufacture and thermal treatments on the static and dynamic mechanical performance. One important requirement for high durability is to remain below the yield stress, where plastic deformation starts, during fuel cell operation. One way of improvement is to enhance the membrane stiffness, characterized by Young modulus, and yield stress by development of composite and cross-linked membranes. Relevant examples will be given. 1. M. L. Di Vona et al. Chem. Mater., 20, 4327 (2008). 2. E. Sgreccia et al., J. Power Sources, 178, 667 (2008).3. E. Sgreccia et al., J. Power Sources, 195, 7770 (2010).4. M.L. Di Vona et al., J. Membrane Sci., 354, 134 (2010).
9:00 PM - B13.9
Palladium-Silver Core-Shell Electrocatalysts for ORR in Alkaline Media.
Ryan Sekol 1 , Xiaokai Li 1 , Gustavo Doubek 1 2 , Peter Cohen 1 , Marcelo Carmo 1 , Andre Taylor 1
1 Chemical &Environmental Engineering, Yale University, New Haven, Connecticut, United States, 2 IPEN, University of São Paulo, São Paulo, SP, Brazil
Show AbstractWith the rising energy demand and need for renewable fuels, alkaline fuel cells (AFCs) have become increasingly considered for use as an alternate power source to combustion engines. There are many reasons why AFCs have advantages over traditional proton exchange membrane fuel cells, including improved kinetics at both the cathode and anode, and increased catalyst stability [1]. Another benefit of AFCs is that both noble and non-noble metals can be used as catalysts[1] specifically, silver decorated on carbon black is known to be active towards oxygen reduction reaction (ORR) [2]. However, the kinetics of silver-based ORR catalysts are slower than platinum [3].In this work a palladium-silver core-shell catalyst was synthesized on multiwalled carbon nanotubes (MWNTs). The Pd@Ag core-shell catalyst is supported on MWNTs because MWNTs have been shown to produce a more active catalyst compared to carbon black [4]. Silver nanoparticles were deposited by a wet impregnation method onto the surface of the MWNTs after acid treatment, resulting in Ag particles of 2.6nm in diameter and a loading of 13.9wt.% Ag. The Pd@Ag core-shell was created using galvanic displacement, which was monitored using the open-circuit voltage method. Galvanic displacement is a single step self-controlled method which takes place just on the surface of the Ag particles. This results in a catalyst that contains very little Pd but has the cyclic voltammetry characteristic peaks of Pd and not Ag. The Pd@Ag/MWNT catalyst has an onset potential that is 40mV more negative than that of the commercial Pd/C catalyst. However, the Pd@Ag/MWNT has a higher current density for ORR compared with both the Ag/MWNT and commercial Pd/C catalysts and a similar current density as Pt/C ETEK. Reference:[1]C. Bianchini and P.K. Shen, Chem. Rev., 109 (2009) 4183.[2]H.-K. Lee, J.-P. Shim, M.-J. Shim, S.-W. Kim and J.-S. Lee, Mater. Chem. Phys., 45 (1996) 238.[3]L. Demarconnay, C. Coutanceau and J.M. Léger, Electrochimica Acta, 49 (2004) 4513.[4]M. Carmo, V.A. Paganin, J.M. Rosolen and E.R. Gonzalez, Journal of Power Sources, 142 (2005) 169.
Symposium Organizers
Maria Luisa Di Vona University of Rome Tor Vergata
Joshua Hertz University of Delaware
Philippe Knauth University of Provence
Harry L. Tuller Massachusetts Institute of Technology
B14: New SOFC Materials and Phenomena
Session Chairs
Scott Barnett
Sossina Haile
Thursday AM, December 01, 2011
Constitution B (Sheraton)
9:30 AM - **B14.1
New Materials for SOFCs: Design or Discovery.
John Kilner 1 2
1 Materials, Imperial College,London, London United Kingdom, 2 I2CNER, Kyushu University, Fukuoka Japan
Show AbstractThe Solid Oxide Fuel Cell (SOFC) is now entering the first stages of commercialisation, but many problems remain to be solved if the devices are to attain their full potential to reduce carbon emissions. Many developers are now moving towards operation of the SOFC at reduced temperatures (>750°C), the so called Intermediate Temperature SOFC (ITSOFC), to explore the inherent advantages of cost reduction and durability. One of the disadvantages of moving to these lower temperatures is that the electrocatalytic activity of the electrodes is much lower. This is particularly true of the cathode, which has often been cited at as the limiting component at low temperatures. The development of low temperature cathodes is thus an area of high priority for SOFC research. This search for new cathode materials has taken two main directions; (a) finding new single phase materials or (b) making composites from conventional materials. For single phase materials it is clear that Mixed Electronic Ionic Conductors (MEIC’s) such as the rare earth perovskites e.g. La1-xSrxCoO3-δ, have the highest activity, as determined by their transport properties, however despite criteria defining the necessary performance of these materials there are no criteria for the selection of new compositions. There are two approaches to the problem of discovering new ITSOFC cathodes; first the conventional methods which attempt to gain insight into mass and electronic transport mechanisms, however this a very slow process and SOFC development times need to be shortened. The second is by combinatorial methods, either experimental or computational, which are, so far, very few in number. The possible compositional spaces to be explored by these combinatorial methods is extremely large and it seems unlikely that experimental approaches alone will be unable to provide rapid discover of new materials. Thus it looks likely that the most successful strategies will involve the use of computational studies to guide highly targeted experimental surveys of limited compositional regions. This paper will review recent work to investigate screening and predictive tools for the discovery of new SOFC materials.
10:00 AM - **B14.2
Versatile Applications of Barium Indate-Based Compounds.
Maria Teresa Caldes 1 , Eric Quarez 1 , Angelique Jarry 1 , Marika Letilly 1 , Annie Le Gal La Salle 1 , Olivier Joubert 1
1 , CNRS-IMN, Nantes France
Show AbstractThe research on solid oxide fuel cell (SOFC and PCFC) is based on both the synthesis of new materials and the design process of the cell. The main advantage of SOFC is that they can work under hydrocarbon fuel at temperature higher than ≈700°C. In the current SOFC systems, the most widely used electrolyte is YSZ which is inexpensive and shows an acceptable conductivity level. But YSZ is very refractory and its major drawback is its reactivity during the sintering process with lanthanum- and strontium-based cathode materials, which leads to the formation of an insulating layer such as SrZrO3 or La2Zr2O7. There is also a great interest to find ceramic based fuel cells, for mobile application, working at low temperature (≈400°C). This can be achieved in PCFC with a ceramic membrane showing a good proton conductivity level. The state of the art perovskite type Yttrium-doped BaCeO3 (called BCY) shows a proton conductivity level above 1mS/cm at 400°C. But due to its high basicity, BCY tends to decompose, in this temperature domain, in air containing CO2. Finding new electrolyte material is one of the issues. This talk deals with the development of solid oxide cells based on a new class of electrolyte materials developed in IMN-Nantes : Ba2In2(1-x)Ti2xO5+x (hereafter called BITx) derived from Ba2In2O5, where indium is substituted by titanium. Two compositions exhibit interesting electrolyte material properties: BaIn0.8Ti0.2O2.6 (BIT0.2) for proton conducting fuel cell (PCFC) and BaIn0.3Ti0.7O2.85 (BIT0.7) for SOFC. We have shown that the progressive filling of oxygen vacancies in the brownmillerite compound Ba2In2O5, concomitant with substitution of Ti for In in Ba2(In1-xTix)2O5+x (0 ≤ x ≤ 0.7)), induces a disorder within the initially ordered array of such vacancies. Thus, for a substitution rate larger than 15%, all compounds adopt a disordered cubic perovskite structure at room temperature exhibiting similar O2- conductivity level at 700°C compared to YSZ. BITx powders can be fully sintered between 1200°C and 1300°C and are compatible with usual perovskite type cathode materials.At 700°C, single SOFC cells built on BIT0.7 shows a total ASR of 0.54Ω.cm2 under hydrogen.All BITx compounds react at low temperature with water vapor to produce Ba2In2(1-x)Ti2xO4+2x(OH)y (0 ≤ x ≤ 0.7; y ≤ 2(1-x)) phases. In this talk, the hydration process of BITx compounds and derivative compounds will be presented. The total conductivity of BITx is mainly protonic up to 500°C depending on the substitution ratio. Proton conductivity similar to that of BCY was measured at 400°C for BIT0.2. On account of equivalent or even better performances compared to this standard material, and to a low reactivity with CO2, a single PCFC cell based on BIT0.2 as electrolyte was evaluated.
10:30 AM - B14.3
Cerium Niobate – Synthesis, Structure and Properties.
Ryan Bayliss 1 , Timothy White 4 5 , Thomas Baikie 4 , Stephen Skinner 1 , Stevin Pramana 4 , Mary Ryan 3 1 , Andrew White 2 , Robert Packer 1
1 Department of Materials, Imperial College London, London United Kingdom, 4 Division of Materials Science & Engineering, Nanyang Technological University, Singapore Singapore, 5 Centre for Advanced Microscopy, Australian National University, Canberra, Australian Capital Territory, Australia, 3 London Centre for Nanotechnology, Imperial College London, London United Kingdom, 2 Department of Chemistry, Imperial College London, London United Kingdom
Show AbstractMaterials with inherent oxygen excess are of great interest for high-temperature electrochemical applications such as solid oxide fuel cells (SOFCs) and oxygen generators due to their fast oxide ion conductivity. The high conductivity observed in these materials is required to reduce the operating temperature of SOFCs, therefore lowering degradation rates and increasing cell operating life. CeNbO4+δ is a promising example of a potential future high performance material. Cerium niobate undergoes a phase transition at ~1073 K from the monoclinic to the tetragonal phase [1] inducing significant effects on oxide ion conductivity [2]. Results here show that the monoclinic crystal structure is preferential for oxide ion conductivity. Single crystal X-ray diffraction, electron diffraction and X-ray spectroscopic techniques (XANES) have been used to gain insight into this unusual class of materials, including in situ measurements to study real time effects of temperature and atmosphere on oxygen excess stability regimes, including reaction kinetics. Work presented here will also include discussion of the effect of alivolent doping to enhance the materials properties in cerium niobate and an analogous structure. A review of the materials potential for future development will also be included.
10:45 AM - B14.4
Synthesis, Structure and Properties of LnBa(Co,Me)2O5+δ (Ln = Nd, Sm, Ho and Y; Me = Fe, Ni, Cu) as Potential Cathodes for SOFCs.
Vladimir Cherepanov 1 , Ludmila Gavrilova 1 , Tatyana Aksenova 1 , Anastasia Podzorova 1 , Nadezhda Volkova 1 , Evgenia Plotnikova 1
1 Chemistry, Ural Federal University, Yekaterinburg Russian Federation
Show AbstractThe polycrystalline samples LnBaCo2-xMexO5+δ (Ln = Nd, Sm, Ho and Y; Me = Fe, Ni, Cu) were prepared by a solid-state reaction and glycerin-nitrate technique. Final anneals were performed at 1273–1373 K in air with intermediate grindings during 100-120 h with following slow cooling to room temperature at the rate of about 100 K/h. Phase identification was made by XRD analysis. The unit cell parameters were refined using Rietveld analysis. It was shown that depending on chemical composition and oxygen content all single phases possess either tetragonal or orthorhombic structure. The changes in unit cell parameters in doped samples were explained by size factor. The homogeneity ranges of solid solutions were determined. Oxygen nonstoichiometry in LnBaCo2-xMexO5+δ was measured by thermogravimetric (TG) analysis within the temperature range 298 ≤ T,K ≤ 1373 in air using Simultaneous Thermal Analyzer STA 409 PC Luxx, Netzsch). The results obtained in dynamic (cooling rate 1 K/min) and static (8-10 h step at constant temperature) conditions were in a good agreement, which confirm a relatively quick exchange of solid and gaseous phases by oxygen. Mass saturation of all samples occurs at about 300 – 350oC upon cooling. The absolute oxygen content of the samples was determined by two methods: (i) reduction in hydrogen flow assuming Ln2O3, BaO and metallic Co and Fe or Ni or Cu as final products and (ii) oxidation-reduction titration. Oxygen content in LnBaCo2-xMexO5+δ evaluated at room temperature increases in iron substituted solid solutions (relatively to undoped samples) and decreases in copper containing phases. Oxygen content in nickel substituted phases remains practically unchanged. Gradual increase of iron leads to the increase of oxygen content while an increase of copper shows opposite effect.Thermal expansion for LnBaCo2-xMexO5+δ was measured using Netzsch DIL 402C dilatometer in the temperature range 298-1373 K in air, with the cooling/heating rate 5 K/min. The average expansion coefficients for the LnBaCo2-xMexO5+δ were calculated. Chemical compatibility with the electrolyte materials Zr0.85Y0.15O2 and Ce0.8Sm0.2O2 have been checked. It was shown that introduction of Fe in all cases always increase the temperature of chemical reaction between the cathode and electrolyte materials while Cu decrease this temperature. All double perovskites reacted with Zr0.85Y0.15O2 at relatively low temperature, while most of them were stable towards to Ce0.8Sm0.2O2.This work was financially supported in parts by the Russian Foundation for Basic Research (project No. 09-03-00620) and the Ministry for Education and Science of the Russian Federation within the Federal Target Program “Research and Teaching Stuff of Innovative Russia for 2009 – 2013”.
11:30 AM - **B14.5
High-Performance Intermediate Temperature Solid Oxide Fuel Cells (IT-SOFCs) with Electrolyte Films Prepared by Electrophoretic Deposition.
Riccardo Polini 1 , Francesco Bozza 1 , Enrico Traversa 1
1 , University of Rome Tor Vergata, Rome Italy
Show AbstractSolid oxide fuel cells (SOFCs) have attracted a considerable attention due to their high-energy conversion efficiency and fuel flexibility. SOFCs use ceramic substances as electrolytes and have shown considerable promise for a variety of applications ranging from mobile devices to stationary power plants. A significant boost to the reduction in the manufacturing cost of SOFCs would be achieved if readily available and easily formed metals, such as ferritic stainless steels, could be used for the interconnect plate and gas manifolding. However, the problems of high temperature corrosion mean this is only realistic if the operating temperature is reduced to temperatures below 800 °C. A further reduction of the operating temperature would also lead to an increase in stack reliability and lifetime.To decrease the operating temperature of SOFCs the internal resistance of the cell must be reduced. This goal can be obtained by using oxygen ion conductors with superior ionic conductivity values at 600–800 °C. Perovskites with composition La1 – xSrxGa1 – yMgyO3–δ, with δ = (x+y)/2, are amongst the most promising electrolyte materials for IT-SOFCs. IT-SOFCs based on LSGM can be operated at 750 °C, and even lower operating temperatures could be achieved by using thin films of LSGM.We obtained remarkable power densities for anode-supported solid oxide fuel cells (SOFCs) based on La0.8Sr0.2Ga0.8Mg0.2O3-δ (LSGM) electrolyte films, fabricated following an original procedure that allowed avoiding undesired reactions between LSGM and electrode materials, especially Ni at the anode. Electrophoretic deposition (EPD) was used for the fabrication of 30 µm-thick electrolyte films. Anode supports were made of La0.4Ce0.6O2-x (LDC). The LSGM powder was deposited by EPD on an LDC green tape-cast membrane added with carbon powder, both as pore former and substrate conductivity booster. A subsequent co-firing step at 1490 °C produced dense electrolyte films on porous LDC skeletons. Then, a La0.8Sr0.2Fe0.8Co0.2O3-δ (LSFC) cathode was applied by slurry-coating and calcined at 1100 °C. Finally, the porous LDC layer was impregnated with molten Ni nitrate to obtain, after calcination at 900 °C, a composite NiO–LDC anode. Maximum power densities of 780, 450, 275, 175, and 100 mW/cm2 at 700, 650, 600, 550, and 500 °C, respectively, were obtained using H2 as fuel and air as oxidant, demonstrating the success of the processing strategy.
12:00 PM - B14.6
Partial Electronic Conductivity and Electrolytic Domain of Bilayer Electrolyte Zr0.84Y0.16O1.92/Ce0.9Gd0.1O1.95.
Tae-Hyun Kwon 1 , Taewon Lee 1 , Han-Ill Yoo 1
1 , WCU Hybrid Materials Program, Department of Materials Science and Engineering, Seoul National University, Seoul Korea (the Republic of)
Show AbstractPartial electronic conductivity and total conductivity have been determined, by Hebb-Wagner polarization method and a.c. impedance spectroscopy, respectively, on bilayer electrolyte Zr0.84Y0.16O1.92(YSZ)/Ce0.9Gd0.1O1.95(GDC) with thickness ratios 10-3/1 and 10-4/1 at 800o, 900o and 1000oC, respectively. While their ionic conductivities remain close to that of GDC, the electronic conductivities are suppressed from that of GDC towards that of YSZ the more the higher the thickness ratio, as expected. Even when the GDC-side is exposed to reducing atmosphere, the electronic conductivity is also suppressed, but to a less extent. It is suggested that oxygen activity distribution is discontinuous across the YSZ/GDC interface under ion-blocking condition, refuting the “continuity hypothesis” that has been usually adopted in calculating the oxygen activity distribution across a multilayer of mixed conductor oxides. The electrolytic domain widths of the bilayer electrolyte are reported depending on temperature, thickness ratio and direction of oxygen activity gradient imposed.
12:15 PM - B14.7
Electrochemistry of Thin La0.6Sr0.4CoO3-δ Cathodes in Free-Standing Micro-SOFC Membranes.
Michel Prestat 1 , Anna Evans 1 , René Toelke 1 , Julia-Maria Martynczuk 1 , Zhen Yang 1 , Ludwig Gauckler 1
1 Nonmetallic Inorganic Materials, ETHZ, Zurich Switzerland
Show AbstractMiniaturized solid oxide fuel cells (micro-SOFC) are believed to constitute one of the technologies that could help satisfy the continuously increasing electric energy demand for small mobile devices such as laptops and cell phones [1,2]. The presentation will essentially focus on thin La0.6Sr0.4CoO3-δ (LSC) electrodes prepared by pulsed laser deposition (PLD) and integration in miniaturized SOFC (micro-SOFC).The cells are manufactured by standard microfabrication processes on silicon chips coated double-side coated with an electrically insulating layer of Si3N4.The LSC layers are deposited on thin (300 nm) free-standing nanocrystalline tetragonal yttria-stabilized zirconia membranes (3YSZ, 390 x 390 microns) prepared by PLD. STEM and SAED analyses evidence that LSC deposition at 450°C with high oxygen pressure (300 mTorr) yields amorphous layers with nanograins and nanoporosity of ca. 5 nm providing a large surface area for oxygen exchange at the LSC/air interface that is believed to be the rate-determining step. Amorphous LSC exhibit higher activity towards oxygen reduction and lower activation energy than crystalline LSC opening opportunities to reduce the fuel cell operating temperature to 500°C and lower.Results on the influence of LSC heat treatment, crystallinity, microstructure and thickness will be presented. The electrochemical performance of micro-SOFC with LSC cathodes in the temperature range of 450-550°C will also be reported.[1] A. Evans et al., J Power Sourc., 194 (2009) 119.[2] A. Bieberle-Huetter et al., J. Power Sourc., 177 (2008) 123.
12:30 PM - B14.8
Understanding Chemical Expansion in Non-Stoichiometric Oxides.
Dario Marrocchelli 1 , Sean Bishop 2 3 , Bilge Yildiz 1 , Harry Tuller 3
1 Department of Nuclear Science & Engineering, MIT, Cambridge, Massachusetts, United States, 2 International Institute for Carbon Neutral Energy Research (I2CNER), Kyushu University, Kyushu, Fukuoka, Japan, 3 Department of Materials Science & Engineering, MIT, Cambridge, Massachusetts, United States
Show AbstractNon-stoichiometric oxides are used in many high temperature energy applications such as solid oxide fuel cells (SOFCs), oxygen permeation membranes, and gas conversion/reformation catalysis. Indeed, many high performance SOFC electrodes, and even electrolytes, exhibit significant oxygen stoichiometry fluctuations with changes in atmosphere (oxidizing to reducing), temperature, and power demand, resulting not only in changes in electrical and phase stability properties, but also in significant mechanical stresses from defect induced lattice parameter changes, also referred to as chemical expansion. For example, an increase in the effective thermal expansion coefficient due to oxygen loss upon heating in air has been observed for both Pr0.1Ce0.9O2-δ (> 200%) and La0.6Sr0.4Co0.2Fe0.8O3-δ (> 50%), SOFC cathode materials. While chemical expansion driven stresses and the ultimate cracking of these materials is a technologically important challenge, the governing mechanisms and strategies to suppress chemical expansion have not been identified to date.In this paper we use atomistic computer simulations, together with experimental data, to elucidate the factors responsible for defect induced chemical expansion observed in CeO2 and ZrO2. We find that chemical expansion is the result of two competing processes, the formation of a vacancy (leading to a lattice contraction) and the cation radius change (leading to a lattice expansion). We model the chemical expansion coefficient as the summation of two terms that are proportional to the cation and oxygen radius change, respectively. This model introduces one empirical parameter, the vacancy radius, which we demonstrate can be reliably predicted from computer simulations, as well as from the experimental data. We then use this model to predict material compositions that minimize chemical expansion in solid oxide fuel cell materials under typical operating conditions.
12:45 PM - B14.9
Electrostriction in Gd-Doped Ceria.
Roman Korobko 1 , Igor Lubomirsky 1
1 Materials and Interfaces, Weizmann Institute of Science, Rehovot Israel
Show AbstractDoped ceria is one of the most important and extensively studied oxygen ion conductors for solid oxide fuel cell or sensor applications. Recent investigations of the microscopic origin of the elastic anomalies in 20% Gd-doped ceria (Kossoy, Adv. Mat. 2009) indicates that in presence of oxygen vacancies, oxygen ions shifts towards CeCe ions. As a result CeCe- VO″ distance becomes much larger than CeCe-OO bond and the lattice undergoes local distortion. Due to this local lattice distortion [CeCe -VO]″ complex behaves as an elastic dipole and as an electric dipole as well. Therefore, it was expected to reorient under external electric field.We investigated electrostriction in strain-free {substrate\\metal\\1μm > Ce0.8Gd0.2O1.9 thin film\\metal} structures by monitoring mechanical response to application of external electrical bias. We found that field-induced stress in Gd-doped ceria is comparable with that of commercial electrostrictors. Low dielectric constant (~24) rules out field compression or relaxor-type electrostriction mechanism. In this view, low relaxation frequency (~180 Hz) and Debye-type relaxation behavior suggests that the electrostriction in doped ceria originates in reorientation of the elastic and electric dipoles under an electric field. Our findings agree with the predictions of Lay and Whitmore (Lay & Whitmore, Phys. Stat. Sol., 1971) based on internal friction measurements.
B15: PEM Electrodes II
Session Chairs
Thursday PM, December 01, 2011
Constitution B (Sheraton)
2:30 PM - B15.1
High Performance Membrane-Electrode Assemblies with Novel Membrane and Electrocatalysts for Direct Methanol Fuel Cells.
Xinsheng Zhao 1 , Wei Li 1 , Yuanqin Zhu 1 , Arun Murthy 1 , Arumugam Manthiram 1
1 , Electrochemical Energy Laboratory & Materials Science and Engineering Program, Austin, Texas, United States
Show AbstractDirect methanol fuel cells (DMFCs) are attractive as a potential power source for various portable applications such as cellular phones, laptop computers, and soldier power as they offer high energy density and use easily manageable liquid methanol fuel. However, the high methanol crossover through the Nafion membrane from the anode to the cathode, the sluggish reaction kinetics of the oxygen reduction reaction (ORR) and the methanol oxidation reaction (MOR), and the dissolution of Ru from the PtRu MOR catalyst pose serious hurdles for the commercialization of DMFC. With an aim to overcome these difficulties, this presentation focuses on the fabrication of a DMFC stack with new polymeric acid-base blend membranes exhibiting suppressed methanol crossover, methanol tolerant ORR catalysts, and durable MOR catalysts. A novel, low-cost blend membrane consisting of sulfonated poly(ether ether ketone) (an acidic polymer) and polysulfone tethered with 2-amino-benzimidazole (a basic polymer) has been synthesized and scaled up for a DMFC stack. It shows high proton conductivity while exhibiting lower methanol crossover compared to plain SPEEK and Nafion 115 due to the insertion of the basic groups into the ionic channel formed by the sulfonic acid groups. The low methanol crossover provides an important advantage of operating these membranes with high concentration of methanol. Carbon-supported Pd-Co catalyst has been synthesized by a modified polyol reduction process and scaled up for a DMFC stack. The synthesis process offers Pd-Co nanoparticles with an average particle size of 4 nm and a narrow size distribution. The Pd-Co/C catalyst offers excellent tolerance to methanol poisoning and lower cost compared to the conventional Pt/C catalyst for oxygen reduction reaction (ORR). Carbon-supported Pt-Sn-CeO2-δ catalyst has been synthesized by a polyol reduction rocess and scaled up for a DMFC stack. The Pt-Sn-CeO2-δ/C catalyst offers much better durability than the conventional Pt-Ru catalyst while exhibiting high activity for MOR. A DMFC stack built with the blend membrane, Pd-Co/C ORR catalyst, and Pt-Sn-CeO2-δ/C MOR catalyst exhibits high performance and better durability when operated with higher concentrations of methanol fuel.
2:45 PM - B15.2
The Discovery and Optimisation of PEMFC Electrocatalysts: Particle Size Effects, New Supports and Non-Noble Metal Systems.
Brian Hayden 1 2 , Jonathan Davies 2 , Claire Mormiche 2 , Audrey Vecoven 2 , Alexander Anastasopoulos 1 , John Blake 1
1 Chemistry, University of Southampton, Southampton United Kingdom, 2 , Ilika Technology Plc, Southampton United Kingdom
Show AbstractAn essential requirement for the successful development and commercialisation of PEM Fuel Cells is to reduce the cost, increase the stability and retain (or increase) the activity of the electrocatalysts. The synthesis of hundreds of model electrocatalysts, produced by a high throughput (HT) physical vapour deposition method [1], and interrogated using HT screening methods [2], provides a powerful tool for catalyst discovery and optimisation. In the case of supported platinum, we show how the particle size and support strongly influences the activity of the catalyst. In the search for more stable alternatives to carbon, we show how the phase of, for example, an oxide such as doped titania critically influences the cathodic oxygen reduction (ORR) activity and stability of the system [3,4]. The support can also strongly influence the CO tolerance of platinum at the anode [5]: The influence of the support in spill-over, electronic and structural influences is discussed. The combination of ab-initio theory and electrocatalyst screening also provides a powerful combination in the search for precious metal alloy and non noble metal alloy catalysts, as well as alternative materials such as carbides. Examples are given for anode hydrogen oxidation (HOR) catalysts such as Pd based alloys [6], tungsten copper alloys and tungsten carbides.1.S. Guerin, B. E.Hayden ; J. Comb. Chem. 8 (2006) 66-73.2.S. Guerin, B. E. Hayden, C. E. Lee, C. Mormiche, A. E. Russell; J.Phys.Chem.B 110 (2006) 14355-14362.3. I. Cerri, T. Nagami, J.C. Davies, C. Mormiche, B.E Hayden; Proceedings of Fundamentals and Developments of Fuel Cells (FDFC) 2011, Grenoble, France, January 19 – 21.B. E. Hayden, D. Pletcher, J.-P. Suchsland and L. J. Williams; Phys. Chem. Chem. Phys. 11 (2009) 9141-9148.5.B. E. Hayden, D. Pletcher, J.-P. Suchsland and L. J. Williams; Phys. Chem. Chem. Phys. 11 (2009) 1564-1570.6.F. A. Al-Odail, A. Anastasopoulos, and B. E. Hayden; Phys. Chem. Chem. Phys. 12 (2010) 11398-11406. Ibid; Topics in Catalysis 54 (2011) 77-82.
3:00 PM - B15.3
Columnar Metal Oxide Catalyst Supports.
Michael Fleischauer 1 , Ryan Tucker 2 , Nicole Beckers 2 , Arman Bonakdarpour 3 , David Wilkinson 3 , Michael Brett 1 2
1 , NRC-National Institute for Nanotechnology, Edmonton, Alberta, Canada, 2 Electrical and Computer Engineering, University of Alberta, Edmonton, Alberta, Canada, 3 Chemical and Biological Engineering, University of British Columbia, Vancouver, British Columbia, Canada
Show AbstractFuel cell durability and cost, which are strongly related to the distribution of the Pt catalyst, continue to affect commercialization efforts. High surface area carbon particles lead to high Pt surface areas but corrode during fuel cell operation.[1] Considerable performance and stability have been demonstrated with 3M’s nanostructured thin film (NSTF) catalyst supports, which consist of crystalline whiskers of a perylene derivative.[2] Although promising, these NSTF pose additional challenges such as limited support conductivity and water management issues.[3]Alternative materials such as metal oxides are actively being pursed to address support stability and conductivity issues.[4,5] We are pursuing a route that combines NSTF porosity with metal oxide performance. Glancing Angle Deposition (GLAD)[6,7] has recently been applied to fuel cell catalyst supports for a broad range of materials including Ti, C, and CrN.[8-10] Nanostructured Ti supports exhibited electrochemical surface areas about 10-15 times higher than smooth Pt films at low loadings (100-200 μg Pt/cm2),[8] in line with 3M’s NSTF performance.Metal oxide performance depends on achieving specific phases. We have recently demonstrated phase and morphology control over structured metal oxides via reducing atmosphere annealing: for example, structured NbOx can be transformed to controlled porosity NbO2, Nb2O5, or NbN1-xOx, depending on the anneal conditions.[11] Here we will present both electrochemical and materials characterization results for various metal oxide morphologies, compositions, and crystalline phases with the intent of evaluating the suitability of GLAD as a method for preparing NSTF catalyst supports.[1] Y. Liu, C. Ji, W. Gu, J. Jorne, and H.A. Gasteiger, J. Electrochem. Soc., 158, B614 (2011).[2] M.K. Debe, A.K. Schmoeckel, G.D. Vernstrom, and R. Atanasoski, J. Power Sources, 161, 1002 (2006).[3] A. Kongkanand and P.K. Sinha, J. Electrochem. Soc., 158, B703 (2011).[4] T. Ioroi, Z. Siroma, N. Fujiwara, S.-I. Yamazaki, and K. Yasuda, Electrochem. Comm., 7, 183 (2005).[5] E. Antolini and E.R. Gonzalez, Solid State Ionics, 180, 746 (2009).[6] K.Robbie and M.J. Brett, J Vac. Sci. & Tech. A, 3, 1460 (1997).[7] US Patents 5,866,204, 6,206,065, 6,248,422, 6,549,253.[8] A. Bonakdarpour, M.D. Fleischauer, M.J. Brett, and J.R. Dahn, Appl. Catal. A, 349, 110 (2008).[9] M. D. Gasda, G. A. Eisman, and D. Gall, J. Electrochem. Soc., 157, B71 (2010).[10] M. D. Gasda, G. A. Eisman, and D. Gall, J. Electrochem. Soc., 157, B113 (2010).[11] R.T. Tucker, M.D. Fleischauer, R.M. Shewchuk, A.E. Schoeller, and M.J. Brett, Mat. Sci. Eng. B, 176, 626 (2011).
3:15 PM - B15.4
Bulk Metallic Glasses as New Materials for PEM Fuel Cells.
Golden Kumar 1 , Sundeep Mukherjee 1 , Marcelo Carmo 1 , Ryan Sekol 1 , Andre Taylor 1 , Jan Schroers 1
1 , Yale University, New Haven, Connecticut, United States
Show AbstractBulk metallic glasses are multicomponent alloys that exist in a wide range of chemical compositions. Furthermore we have recently shown that they can be molded on the nanoscale [1], which provides very large surface area structures. Motivated by these characteristics, we have explored the use of a Pt-based BMG (Pt57.5Cu14.7Ni5.3P22.5) for the use as a electrocatalysts in direct alcohol fuel cells. Both features, activity and durability, of the BMG are superior over benchmark Pt/C catalysts [2]. Remarkable, when comparing to catalysts of carbon nanotube which are decorated with Pt nanoparticles, the durability of the BMG is significantly higher. The activity of these BMG catalysts is further enhanced by de-alloying mediated surface area enhancement. We are exploring strategies to develop new alloys with accelerated de-alloying as potential catalysts. The ability to shape BMGs across length scales with the ease of plastics [3] is also explored for current collector bipolar plates. A prototype micro fuel cell consisting of bipolar plate, electrode, and catalysts fabricated from BMG is introduced.1.Kumar, G., H.X. Tang, and J. Schroers, Nanomoulding with amorphous metals. Nature, 2009. 457(7231): p. 868-872.2.Carmo, M., et al., Bulk Metallic Glass Nanowire Architecture for Electrochemical Applications. Acs Nano, 2011. 5(4): p. 2979-2983.3.Kumar, G., A. Desai, and J. Schroers, Bulk Metallic Glass: The Smaller the Better. Advanced Materials, 2011. 23: p. 1566.
3:30 PM - B15.5
Role of Support Materials in Nanoengineered Alloy Catalysts for Fuel Cells: Tungsten Carbide vs. Carbon Black.
Ming Nie 1 , Jin Luo 1 , Rameshwori Loukrakpam 1 , Jun Yin 1 , Chuan-Jian Zhong 1
1 Department of Chemistry, State University of New York at Binghamton, Binghamton, New York, United States
Show AbstractThe electrocatalytic performance of alloy catalysts in fuel cells depends on structures and interactions of the supporting materials. This report describes recent findings of an investigation of nanoengineered platinum vanadium-iron (PtVFe) catalysts supported on two different supporting materials: tungsten carbide (WC) and traditional carbon black (C). The catalysts were prepared with controlled sizes and compositions that were thermally treated under controlled temperature and atmosphere. Examples such as WC-supported and C-supported Pt35V23Fe42 catalysts treated at 400 degree(C) and 800 degree(C) will be described. Enhanced electrocatalytic activities and stability for oxygen reduction reaction were observed depending on a combination of the supporting materials and the thermal treatment temperature. The interaction between trimetallic alloy nanoparticles and the support was found to play an important role in enhancing the electrocatalytic activity. The differences between tungsten carbide support and carbon black support will also be discussed.
3:45 PM - B15.6
Doped Metal Oxide Nanoparticles for Catalyst Support Applications in Proton Exchange Membrane Fuel Cells.
Chinmayee Subban 1 , Francis DiSalvo 1
1 Chemistry & Chemical Biology, Cornell University, Ithaca, New York, United States
Show AbstractThe promises of high efficiency and low emissions have made fuel cells an attractive alternative to current energy conversion technologies. Low temperatures of operation and fast start-stop capabilities have made the proton exchange membrane fuel cell (PEMFC) of interest for portable electronics and automobiles. Unfortunately, the current materials used in PEMFCs are not adequately durable. Studies have shown that the carbon black catalyst supports in PEMFCs degrade over time resulting in the aggregation of the catalyst nanoparticles, which affects the overall performance of the fuel cell. A desirable non-carbon catalyst support should prove to be stable under low pH (1-2) and potentials up to +1.5 V, be conducting (at least 0.1 S/cm) and have an open porous morphology. Further, the catalyst support should also be capable of binding Pt or Pt-based catalysts. However, under the pH and potential conditions of a PEMFC, sulfides, carbides and nitrides are all thermodynamically driven to oxidize or hydrolyze to oxides, at least at the surface. According to Poubaix diagrams, certain oxides with metals in their highest oxidation states appear to be stable under these conditions in air/water. However, since in each case the metal is in its highest oxidation state, these oxides are not conducting, but these oxides can be partially reduced or doped with other metal cations, resulting in metallic or semiconducting behavior. Here we discuss the synthesis, characterization, chemical stability, and electrochemical testing of a family of such conducting doped metal oxides that can potentially replace the currently used carbon black catalyst supports in PEMFCs.
4:00 PM - B15: PEM el 2
BREAK
B16: PEM Materials III
Session Chairs
Thursday PM, December 01, 2011
Constitution B (Sheraton)
4:30 PM - B16.1
Rational Design and Synthesis of Advanced Electrocatalysts for Energy Conversion Applications - From Extended Surfaces to Nanoscale Architectures.
Chao Wang 1 , Nenad Markovic 1 , Volislav Stamenkovic 1
1 Materials Science Division, Argonne Nat Lab, Argonne, Illinois, United States
Show AbstractHighly efficient chemical-electrical energy conversion has become the primary target for the practical application of renewable energy technologies. This to a large extent relies on the development of novel electrocatalysts with high catalytic activity, long durability, and competitive cost effectiveness. Conventional platinum (Pt) catalysts that have been widely employed in fuel cells are not only expensive, but also scarce which have limited their large-scale applications. Moreover, Pt that is generally considered to be chemically inert becomes unstable when exposed to hostile electrochemical environments. Here I introduce our systematic approach toward the rational design and synthesis of advanced Pt-bimetallic and -multimetallic electrocatalysts for the oxygen reduction reaction (ORR) – the key reaction in fuel cells. Via combinational studies on extended surfaces and high-surface-area nanocatalysts, we have managed to control and finely tune the structure architecture of the catalysts at nanoscale. Critical parameters such as particle size, shape, alloy composition and composite profile were screened and optimized for improving ORR catalytic activity and durability. These studies plus further theoretical calculation and simulation have provided us comprehensive understanding of the structure-function correlation in the catalysts, which could have great potential toward guiding the development of other functional nanomaterials.
4:45 PM - B16.2
Liquid-Phase Reductive Deposition of Cu-ZnO Catalysts for Mobile-Type Hydrogen Generator.
Noritoshi Yagihashi 1 , Masafumi Nakaya 2 , Kiyoshi Kanie 2 , Atsushi Muramatsu 2
1 Graduate School of Engineering, Tohoku University, Sendai Japan, 2 Institute of Multidisciplinary Research for Advanced Materials, Tohoku University, Sendai Japan
Show AbstractThe small fuel cell systems have been developed as an important alternative for conventional dry batteries or rechargeable lithium-ion batteries. In order to construct the small fuel cell system, the hydrogen supply system must be miniaturized. The methanol steam reforming with Cu-ZnO catalyst in the microreactor is focused as one of the most useful hydrogen supply system because of an advantage in high hydrogen generation efficiency. The conventional supported catalyst microreactor is prepared under high temperature and high pressure condition. However, this method has a disadvantage to deteriorate catalytic activity by sintering catalyst nanoparticles in high temperature so that preparation procedure of catalyst supported inside of microreactor under the rather mild conditions should be developed. In this study, the improvement of the preparation method of Cu-ZnO nanoparticles on alumina into micro-channels of a casted microreactor has been investigated by using liquid-phase reduction method.The alumina supported Cu-ZnO catalyst was prepared as follows. Cu and Zn precursors were dissolved into water. Citric acid and L – serine were added into the solution as a chelating agent. Then γ-alumina powder was added into the solution and well dispersed by ultrasonication. The resultant solution, pre-cooled down to 0 °C, was mixed with NaBH4 aqueous solution as a reducing agent, which was also kept as 0 °C with vigorously stirring. This solution was heated up to 100 °C to reduce metal ions. As-prepared samples were filtrated from the solution and purified with ion-exchanged water, then dried at room temperature. The size and shape of as-prepared nanoparticles were characterized by TEM, and the crystal structure was evaluated by XRD.From TEM images of the resulting nanoparticles on alumina prepared without chelating agent, irregular shaped nanoparticles with the size of 20 nm were observed. These nanoparticles were not adsorbed on alumina. When serine and citric acid were used as chelating agent, spherical nanoparticles with 10 nm in diameter as well as rod shape nanoparticles with 100 nm in long axis were obtained. These nanoparticles were selectively formed on alumina surface. The XRD patterns of each sample suggested that both nanoparticles consisted of Cu, ZnO and γ-Al2O3. Since these chelating agents would coordinate metal ions and affect the state of reaction, the size of particles might be controlled Cu and ZnO nanoparticles adsorbed on alumina were successfully obtained by liquid-phase reduction method, and the particle size of Cu and ZnO nanoparticles was controlled and by using chelating agents. In addition, the in-situ preparation of Cu-ZnO nanoparticles on the channel of microreactor by the above method and catalytic activity of resulting alumina-supported Cu-ZnO nanoparticles for methanol steam reforming reaction will be also presented.
5:00 PM - B16.3
Block Copolymer Directed Synthesis of Ordered Intermetallic PtPb Nanocatalysts in Ordered Large Mesoporous Carbon/Silica Composites for High Performance Direct Formic Acid Fuel Cell Anodes.
Jongmin Shim 1 , Jaehyuk Lee 1 , Youngjin Ye 1 , Jongkook Hwang 1 , Soo-Kil Kim 2 , Tae-Hoon Lim 2 , Ulrich Wiesner 3 , Jinwoo Lee 1 4
1 Chemical Engineering, Pohang University of Science and Technology (POSTECH), Pohang Korea (the Republic of), 2 Center for Fuel Cell Research, Korea Institute of Science and Technology, Seoul Korea (the Republic of), 3 Materials Science and Engineering, Cornell University, Ithaca, New York, United States, 4 School of Environmental Science and Engineering, Pohang University of Science and Technology (POSTECH), Pohang Korea (the Republic of)
Show AbstractThis study demonstrates the simple synthesis of well-dispersed intermetallic PtPb nanoparticles in an ordered mesoporous carbon/silica composites by employing an amphiphilic diblock copolymer assisted co-assembly of hydrophobic metal precursors and hydrophilic carbon and silica precursors; for use as an anode catalyst in direct formic acid fuel cells (DFAFCs). The final materials have a two-dimensional (2-D) hexagonal type structure with uniform and large pores (>30 nm), in which intermetallic PtPb nanocrystals are highly dispersed. The materials show more than 10 times higher mass activity and significantly lower onset potential for formic acid oxidation as compared to commercial Pt/C, as well as high stability due to better resistivity toward CO poisoning. When the resulting catalysts were used for DFAFC single cells, the maximum power density at 50 °C was higher than that of the commercial Pt/C showing that the presented PtPb in OMCS catalysts can be practically applied as real fuel cell catalysts for DFAFC.
5:15 PM - B16.4
Gas Diffusion Media for Proton Exchange Membrane Fuel Cells Made from Carbon Fibers with Controlled Conductivity.
Paul Nicotera 1 , Robert Evans 2 , Christopher Weaver 2 , Chunxin Ji 1 , Po-Ya Abel Chuang 1
1 Electrochemical Energy Research Lab, General Motors, Honeoye Falls, New York, United States, 2 , Engineered Fibers Technology, Shelton, Connecticut, United States
Show AbstractConventional Diffusion Media (DM) is relatively expensive, due to both the high strength, small tow polyacrylonitrile (PAN) based carbon fiber and high heat treatment temperatures (greater than 1600°C) used in its production. Both the PAN fiber raw material and the carbon fiber paper impregnated with phenolic resin are heat treated in separate steps. Significantly cheaper DM can contribute to meeting the overall proton exchange membrane (PEM) fuel cell stack cost target for automotive application. The present study involved the characterization of DM samples made with different types of carbon fibers, which spanned a range of electrical resistivity from 0.009 to 10 Ohm m. The carbon fibers were fabricated by continuously heat treating PAN fibers at maximum furnace temperatures from about 900 to 2600°C. It was found that the more conductive fibers were required to maintain state-of-the-art fuel cell performance with the conventional style of DM substrate (wet-laid, resin-impregnated, and compression-molded carbon fiber paper). However, the most conductive carbon fibers did also enable nearly state-of-the-art fuel cell performance with a reduced DM heat treatment temperature of 950°C, and improved performance with 2250°C heat treatment of the DM. A high-volume cost model is presented that predicts the potential to lower DM cost by an estimated 15% based on the reduced carbon fiber paper heat treatment temperature. The model calculations indicate that the DM cost depends more strongly on the final paper carbonization temperature than the fiber raw material heat treatment temperature.
5:30 PM - B16.5
Controlled Segregation of Au-Pt Nanocrystal Alloy for Efficient Small Organic Molecule Electro-Oxidation Catalyst.
Jin Suntivich 1 , Zhichuan Xu 2 3 , Junhyung Kim 2 , Christopher Carlton 2 , Lawrence Allard 4 , Kimberly Hamad-Schifferli 3 , Hubert Gasteiger 5 , Yang Shao-Horn 1 2
1 Materials Science and Engineering, Massachusetts Institute of Technology, Cambridge, Massachusetts, United States, 2 Mechanical Engineering, Massachusetts Institute of Technology, Cambridge, Massachusetts, United States, 3 Biological Engineering, Massachusetts Institute of Technology, Cambridge, Massachusetts, United States, 4 Materials Science & Technology Division, Oak Ridge National Laboratory, Oak Ridge, Tennessee, United States, 5 Chemistry, Technische Universität München, Garching Germany
Show AbstractThe ability to control the surface composition of bi-metallic nanocrystal alloys can provide a new avenue to rationally design a catalytic site that is more effective than a nanocrystal that has only its bulk composition controlled. We have synthesized Au0.5Pt0.5 nanocrystals [1, 2] and applied adsorbate driven surface segregation strategy to develop a series of model Au-Pt nanocrystal electrocatalysts with either Au-rich or Pt-rich surface to demonstrate that the surface composition controlled Au-Pt nanocrystals can be more effective than the traditional Pt nanocrystal for CO and methanol oxidation reaction electrocatalysis. We quantify the degree of surface enrichment using specific electrochemical adsorption and aberration-corrected Energy Dispersive X-ray spectroscopy (EDX), which allow us to propose the CO and methanol oxidation mechanism on the Au-Pt nanocrystal surfaces.Reference[1.] Lu, Y. C.; Xu, Z. C.; Gasteiger, H. A.; Chen, S.; Hamad-Schifferli, K.; Shao-Horn, Y., J. Am. Chem. Soc. 2010, 132, 12170-12171.[2.] Xu, Z. C.; Carlton, C. E.; Allard, L. F.; Shao-Horn, Y.; Hamad-Schifferli, K., J. Phys. Chem. Lett. 2010, 1, 2514-2518.
5:45 PM - B16.6
Chemical Functionalization of C/Polymer Electrode Materials for Fuel Cell Applications.
Martin Przyklenk 1 2 , Martin Heinen 2 , Volker Peinecke 2 , Nils Hartman 1 2
1 Physical Chemistry , University of Duisburg-Essen, Essen Germany, 2 NanoEnergieTechnikZentrum, University of Duisburg-Essen, Duisburg Germany
Show AbstractWater management remains a problem in common hydrogen oxygen fuel cells. In particular, during operation, condensation of water in the channel structure of the bipolar electrodes eventually blocks gas flow and results in intermittent power losses. A promising approach in order to tackle this problem considers coating of the bipolar plates via modification of their wettability. For this purpose, commercial bipolar plates, consisting of a standard C/Polypropylene composite, are chemically modified via oxygen plasma activation and silanization using distinct precursor molecules including perfluorinated and amino-functionalized silanes. In conjunction with the inherent micro-/nanostructure of the polished bipolar plates this approach allows one to create superhydrophilic and superhydrophobic surfaces, whereas - because of the ultrathin nature of the coating - the excellent electrical conductivity of the material essentially remains unchanged. For characterization contact angle measurements, infrared spectroscopy, optical profilometry and scanning electron microscopy are used. The dynamic wetting behavior is recorded using a digital camera. Work in progress addresses the implementation of silane-coated bipolar plates in fully-functional fuel cells in order to test the performance under standard conditions. Future work will also consider the integration of NPs at the electrode interface in order to further tune their roughness and wettability.
Symposium Organizers
Maria Luisa Di Vona University of Rome Tor Vergata
Joshua Hertz University of Delaware
Philippe Knauth University of Provence
Harry L. Tuller Massachusetts Institute of Technology
B17: Electrode Materials for SOFC and PEM I
Session Chairs
Friday AM, December 02, 2011
Constitution B (Sheraton)
9:30 AM - **B17.1
The Use of Hydrocarbon Fuels in Micro Tubular Solid Oxide Fuel Cells.
Nigel Sammes 3 , Toshio Suzuki 1 , Toshiaki Yamaguchi 1 , Y. Funahashi 2
3 Department of Chemical Engineering, Pohang University of Science and Technology, Pohang Gyeonbuk Korea (the Republic of), 1 , AIST, Nagoya Japan, 2 , FCRA, Nagoya Japan
Show AbstractMicro-tubular (sub mm-range) anode supported SOFC’s have a number of advantages over traditional tubular SOFC systems. They can be stacked to produce high volumetric power densities, as well as have very fast heating/cooling rates. In addition, the micro tubular design is an ideal shape for realizing high volumetric power density and high robustness, which makes them attractive for use in many applications including auxiliary power units and potable power devices. In the present study, anode tubes were made from NiO powder, Gd0.2Ce0.8O2-x (GDC), poly methyl methacrylate beads (PMMA), and cellulose. After adding the proper amount of water, these powders were mixed and extruded using a piston cylinder type extruder. An electrolyte was prepared on the surface of the anode tube by dip-coating a slurry which consisted of the GDC powder used in the anode tube preparation, and co-sintered at 1100-1400 °C for various times in air. A cathode was also prepared by dip-coating a slurry of La0.6Sr0.4Co0.2Fe0.8O3-y (LSCF) powder, the GDC powder, and organic ingredients. After the dip-coating process, the tubes were dried and sintered at 1000°C for 1 h in air. Hydrogen (humidified by bubbling water at room temperature) was flowed inside of the tubular cell at various rates, to investigate the output potential of the microtubular SOFC’s. Single cell performance tests were then conducted using wet H2 fuel in the temperature range of 450~600 oC. The power density of the cell was 270, 630, 1020, and 1300 mW/cm2 at 450, 500, 550 and 600 oC operating temperatures, respectively. Although these micro-tubes give very promising results on hydrogen fuel, the use of hydrocarbon fuels must be considered from the “end-users” point of view. Hence, in this study, we tested a number of different logistical fuels at the intermediate temperature of operation below 650oC; the results from these fuels will be discussed.
10:00 AM - B17.2
The Effect of Ceria Based Catalysts on Electrochemical Oxidation and Carbon Deposition of Dry H2S-Containing Methane over LST – Ceria Impregnated Anode for High Temperature SOFC Applications.
Milad Roushanafshar 1 , Jing-Li Luo 1 , Adrien L. Vincent 1 , Karl. T. Chuang 1 , Alan R. Sanger 1
1 Chemical & Materials Engineering, University of Alberta, Edmonton, Alberta, Canada
Show AbstractSolid oxide fuel cells (SOFCs) are electrochemical devices for converting the chemical energy of a fuel into electrical energy. High operating temperature and oxygen conducting electrolyte enable SOFCs to use different types of fuels including: hydrogen, syngas and various hydrocarbons, notably methane. As a hydrocarbon fuels is a challenging issue requiring considerations of material selection and structure development to mitigate carbon deposition and sulfur deactivation. Lanthanum strontium titanate (LST; La0.4Sr0.6TiO3±δ) is an electronic conductive material with a thermal expansion coefficient (TEC) similar to YSZ which can be used as the anode material in SOFC. Furthermore, it shows high chemical stability at the presence of high concentrations of H2S (10 %). The performance of a cell was enhanced by the inclusion of hydrogen sulfide in the feed when LST was used as the anode. In this research, the effect of the presence of H2S (0.5%) in the feed on the electrochemical oxidation of methane is investigated. LST impregnated porous YSZ was the anode material. Different ceria based catalysts impregnated into the anodes were compared as catalysts for methane oxidation. Mass spectroscopic gas analysis, electrochemical impedance spectroscopy (EIS), potentiodynamic and conductivity measurement tests were used to identify the effect of H2S. The performance of the cell significantly was enhanced when H2S (0.5%) was present in methane. In addition, the electrical conductivity and the polarisation resistance of the anode material improved when H2S was present in the feed. Addition of ceria based catalysts into the anode structure improved the performance of the cell three-fold. The effects of H2S and ceria catalysts on carbon deposition also were evaluated.
10:15 AM - B17.3
Carbon-Free SnO2-Supported PEFC Electrocatalysts with Durability against Voltage Cycling.
Kazunari Sasaki 1 2 3 , Fumiaki Takasaki 2 , Yuma Takabatake 2 , Kohei Kanda 2 , Shingo Hayashi 2 , Zhiyun Noda 1 , Shunsuke Taniguchi 1 , Akari Hayashi 1 3 , Yusuke Shiratori 2 3
1 International Research Center for Hydrogen Energy, Kyushu University, Fukuoka Japan, 2 Faculty of Engineering, Kyushu University, Fukuoka Japan, 3 International Institute for Carbon-Neutral Energy Research (WPI), Kyushu University, Fukuoka Japan
Show AbstractLong-term durability of electrocatalysts is essential for polymer electrolyte fuel cells (PEFCs), where electrocatalyst support materials act as a very important role. In this study, semiconducting oxides, especially SnO2, are considered as an alternative support to the conventional carbon black catalyst support to realize sufficient durability. Thermochemical calculations were applied to derive pH-potential (Pourbaix) diagrams for almost all elements. Among stable materials in strongly acidic environment at 1.0 V vs. standard hydrogen electrode, we can select elements such as Sn, Ti, Nb, Ta, W, and Sb, stable under PEFC cathode conditions [1]. In PEFCs, fluctuation of cell voltage up to higher potentials can cause oxidation-induced carbon support corrosion especially for cathode electrocatalysts. We have been studying the electrocatalysts using various oxide supports to solve these issues. FESEM micrography of the Pt electrocatalyst supported on SnO2 revealed that Pt nano-particles (with ca. 3nm in diameter) were homogeneously distributed on the support material. Pt/SnO2 electrocatalyst exhibited electrochemical properties comparable to Pt/C. Further modification in the electronic conductivity of SnO2 may be expected by doping with hypervalent (e.g. Nb5+) or hypovalent (e.g. Al3+) ions. The electrochemical surface area (ECSA) of Pt/C rapidly decreased within several thousand times of voltage cycles due to carbon corrosion. In contrast, Pt/SnO2-based electrocatalysts exhibited considerably longer durability compared to Pt/C. Even after 10,000 times of voltage cycles, the carbon-free Pt/Sn0.98Nb0.02O2 electrocatalyst still kept sufficient ECSA above 30 m2 g-1. Furthermore, voltage cycling tests have been done for Pt/SnO2 up to 60,000 cycles. These results indicate considerable durability of SnO2-supported Pt electrocatalysts against voltage cycling.References[1] K. Sasaki, F. Takasaki, Z. Noda, S. Hayashi, Y. Shiratori, K. Ito, ECS Transactions, 33, 473-482 (2010). [2] A. Masao, S. Noda, F. Takasaki, K. Ito, and K. Sasaki, Electrochem. Solid-State Lett., 12 (9), B119-B122 (2009).[3] F. Takasaki, Z. Noda, A. Masao, Y. Shiratori, K. Ito, and K. Sasaki, ECS Transactions, 25 (1), 831-37 (2009).
10:30 AM - B17.4
Nano-Scale X-Ray Computed Tomography of Polymer Electrolyte Fuel Cell Electrodes.
William Epting 1 , Jeff Gelb 2 , Shawn Litster 1
1 Mechanical Engineering, Carnegie Mellon University, Pittsburgh, Pennsylvania, United States, 2 , Xradia, Inc., Pleasanton, California, United States
Show AbstractThe catalyst layers of polymer electrolyte fuel cells (PEFCs) are porous layers consisting of carbon and platinum nano-particles, and polymer electrolyte binder. Currently, the high cost of Pt catalyst results in the catalyst layers being the largest component cost for PEFC stacks [1]. Furthermore, this material cost will not be ameliorated by mass production. The proper composition and organization of these catalyst layer materials for fast oxygen and proton transport and high electrochemical activity is key to achieving high performance, long lifetimes, and low costs.
Here we investigate the micro-structure of PEFC catalyst layers using nano-scale X-ray computed tomography (nano-CT) with a resolution of 50 nm and voxel side lengths of 32.5 nm. The benefits of X-ray CT include being non-destructive and able to image samples in ambient and controlled environments for in-situ experiments [2]. We have processed and analyzed higher resolution transmission electron microscopy (TEM) images to identify the information lost with 50 nm resolution given the roughly 5 nm and 40 nm diameters of the Pt and carbon particles, respectively. The TEM analysis indicates that the nano-CT resolution is sufficient for resolving the catalyst particle agglomerates and the pore spaces between them. To further verify the nano-CT, we performed mercury intrusion porosimetry (MIP) measurements on the samples and conducted morphological MIP simulations on the 3D nano-CT reconstructions. This MIP analysis demonstrated agreement for the cumulative pore volume distribution down to pore diameters of 50 nm.
The computational reconstructions and size distributions obtained with nano-CT can be used for evaluating catalyst layer preparation, performing pore-scale simulations, and extracting effective morphological parameters for large-scale computational models. For example, with nano-CT we have imaged two electrodes having different preparations, with one yielding larger particle agglomerates. We analyzed the volumetric pore size and agglomerate size distribution for both electrodes to evaluate the effect of fabrication procedure on 3D electrode micro-structure. Furthermore, we have identified that the distribution of agglomerate sizes has important implications for modeling reaction rates.
1. Sinha, J. and Y. Yang. Direct Hydrogen PEMFC Manufacturing Cost Estimation for Automotive Applications. in 2010 DOE Annual Merit Review. 2010. Washington, DC.
2. Büchi, F., et al., Determination of Local GDL Saturation on the Pore Level by In Situ Synchrotron Based X-ray Tomographic Microscopy. ECS Transactions, 2010. 33(1): p. 1397-1405.
11:00 AM - B17: SOFC/PEM 1
BREAK
B18: Electrode Materials for SOFC and PEM II
Session Chairs
Friday PM, December 02, 2011
Constitution B (Sheraton)
11:30 AM - B18.1
Novel Alloy Oxide Electrocatalysts for Use in Hydrogen Halogen Regenerative Fuel Cells.
Brian Huskinson 1 , Sujit Mondal 1 , Michael Aziz 1
1 , Harvard School of Engineering and Applied Sciences, Cambridge, Massachusetts, United States
Show AbstractElectrocatalysts for halogen reduction and halide oxidation are important for halogen-based electrochemical cells such as halogen flow batteries, which have applications in grid-scale and intermittent renewable electrical energy storage. We report a family of novel nano-structured electrocatalytic alloy oxides, synthesized using standard and non-standard techniques. These alloys have very low precious metal content (as low as 1 at.% ruthenium), excellent catalytic activity with respect to both halide oxidation and halogen reduction, good electrical conductivity, and good corrosion resistance in highly acidic environments. Synthesis procedures and the results of tests of electrocatalytic performance and stability will be reported. We will also report on tests done in a fuel cell, with very low ruthenium catalyst loadings on the cathode side approaching 0.1 mg/cm2. The cell exhibits virtually no activation loss, allowing for very high efficiency operation.
11:45 AM - B18.2
Construction of a Carbon Nanotube-Based Fuel Cell Which Exceeds 2015 DOE Targets.
Neetu Jha 1 , Palanisamy Ramesh 1 , Mikhail Itkis 1 , Robert Haddon 1
1 Chemistry, UCR, Riverside, California, United States
Show AbstractWe demonstrate the first prototype polymer electrolyte membrane fuel cell (PEMFC), which meets and in some instances, significantly exceeds the DOE 2015 targets for automotive applications. By performing the surface purification of a commercial single walled carbon nanotube (P3-SWNT) catalyst support material, we are able to enhance the oxygen reduction reaction (ORR) and fuel cell cathode performance of a Pt3Co catalyst alloy in a very thin fuel cell form factor. A membrane electrode assembly (MEA) fabricated with nafion membrane, Pt3Co-P33-SWNT cathode (0.03 mgPt/cm2) and a commercial Pt-carbon black (CB) anode (0.04 mgPt/cm2) is shown to reach a peak power of 0.7 W/cm2, giving a Pt mass activity of 0.77 mA/gPt and Pt specific power density of 0.14 gPt/kW – both of which exceed the 2015 DOE targets (Mass activity : 0.44 A/mgPt at 0.9 V and Pt specific power density: 0.2 gmPt/kW at 0.65 V).
12:00 PM - B18.3
High Efficiency Cathode/Current Collector Layers for Solid Oxide Fuel Cells Prepared by Polymeric Precursor Infiltration.
Aligul Buyukaksoy 1 , Vladimir Petrovsky 1 , Fatih Dogan 1
1 Materials Science and Engineering, Missouri University of Science and Technology, Rolla, Missouri, United States
Show AbstractUtilization of polymeric precursors provides continuous infiltration of high surface area nanoparticles into porous SOFC electrodes. Symmetrical electrolyte supported structures were used for cathode/current collector investigation. Cathode/current collector layers were prepared by infiltrating polymeric LSM precursor into initial porous layers of Pt, YSZ, and Pt/YSZ double layers and impedance spectroscopy was used as characterization technique. All measurements were carried out at 800 °C. Infiltration of LSM into all porous structures showed significant decrease in the cathode polarization resistance; however degrees of improvement and long term stability were different. It was observed that introduction of porous YSZ layer was necessary to achieve highly efficient and stable cathode/current collectors. Single YSZ layer infiltrated with polymeric LSM precursor showed cathode polarization resistance ~0.040 Ohm.cm2 and good long term stability. The best results were obtained from infiltrated double layer Pt/YSZ electrodes. Initial cathode polarization resistance increased from 0.022 Ohm.cm2 to 0.035 Ohm.cm2 during first 40 hours of testing and remained stable afterwards. This study showed that polymeric LSM precursor infiltration into porous YSZ and Pt/YSZ layers yields highly efficient and stable cathodes.
12:15 PM - B18.4
Properties and Performance of New Perovskite Composite Cathode for IT-SOFC.
Sooyeon Seo 1 , Donghee Yeon 1 , Kyeongseok Moon 1 , Sungjin Ahn 1 , Jusik Kim 1 , Heejung Park 1 , Chan Kwak 1
1 Functional Material group, Samsung Advanced Institute of Techonology (Samsung Electronics) , Yongin-si, Kyeonggi-do Korea (the Republic of)
Show AbstractPerovskite-type composite material ( BSCFZ - LSCF ) were prepared and characterized as cathode for intermediate temperature SOFC ( < 750℃). Thermal expansion coefficient of Zn-doped BSCFZ was lower than undoped-BSCF (Ba0.5Sr0.5Co0.8Fe0.2O3-δ ) from 30 to 800 ℃ in air, which was associated with the loss of oxygen. The electrical conductivity of BSCFZ-LSCF composite was improved over BSCFZ owing to the high electrical conductivity of LSCF. The polarization resistance of BSCFZ-LSCF composite was 0.08 Ωcm2 at 600℃, which was nearly 60% lower than that of BSCFZ electrode. The performance degradation of BSCFZ-LSCF electrode in single cell was investigated. To achieve a guarantee of reliability in real application, BSCFZ-LSCF composite were applied to tubular cell (50cm) as cathode and showed the good power density ( P = 0.46 W/cm2) at 700℃. The result showed that BSCFZ-LSCF was highly promising cathode for reduced temperature SOFCs.
12:30 PM - B18.5
Electronic Structure and Electrochemical Properties of Fe-Doped BaZrO3 for SOFC Cathode.
Dong Young Kim 1 , Shogo Miyoshi 1 , Takashi Tsuchiya 1 , Shu Yamaguchi 1
1 Department of Materials Engineering, Tokyo University, Tokyo Japan
Show Abstract It is essential to develop electrode materials of proton(H) conducting SOFCs(H-SOFC) to decrease operating temperature. While the most important requirements for cathode materials of H-SOFC are both high proton-electronic conductivity and high surface reactivity. In a precedent study, the electrochemical properties of acceptor-doped BaPrO3 [1] have been investigated in expectation of mixed protonic-electronic conductivity. However, its proton solubility and conductivity are not high enough for use as oxide cathode. In this study, we have tried to develop a novel material system which possesses a high electronic conductivity with high catalytic activity for the cathode reaction for H-SOFC. One of possible candidates is 3d-transition metal ion M(tr3+) doped proton conducting perovskite oxide, in which electronic charge carrier is introduced by M(tr3+)-(O-) (h. on O2-) network to proton conducting matrix of BaZrO3. BaZr1-xFexO3 (x=0.1, 0.2 and 0.3) pellets have been fabricated by sintering with powders synthesized with a Pechini-method. Their electronic structure is analyzed with X-ray spectroscopy (X-ray Absorption Spectroscopy, Emission Spectroscopy) and UV-visible light absorption analysis. The hole concentration on O2p orbital observed in the XAS spectra increases with Fe-doping level. But a new peak in Fe2p XAS grows when x>0.3 in BaZr1-xFexO3, suggesting change in the hole and iron ion behavior, which can be attributed to the formation of Fe4+(3d4) state by the reaction, (Fe3+)-(O-)=(Fe4+)-(O2-), induced by the formation of "Fe-O-Fe-O-Fe" network. The effect of the electronic structure variation is evaluated by an electrical conductivity measurement. These results will be presented for discussion based on the auto-ionization model expressed as (Pr4+)-(O2-)=(Pr3+)-(O-)[1].Reference[1] S. Mimuro et al., Solid State Ionics, 178 (2007) 641-647.