Symposium Organizers
Andrew M. Herring Colorado School of Mines
John B. Kerr Lawrence Berkeley National Laboratory
Steven J. Hamrock 3M Fuel Cell Components Program
Thomas A. Zawodzinski Case Western Reserve University
Tuesday PM, April 06, 2010
Room 3005 (Moscone West)
9:00 AM - **FF1.1
The Electrolyte Problem in Rechargeable Lithium Batteries.
Harry Allcock 1 , Shih-To Fei 1 , David Lee 1
1 Chemistry, The Pennsylvania State University, University Park, Pennsylvania, United States
Show AbstractThe Electrolyte Problem in Rechargeable Lithium Batteries.Harry R. Allcock*, Shih-To Fei, David K. LeeDepartment of ChemistryThe Pennsylvania State University104 Chemistry BuildingUniversity Park, PA 16802A major challenge in large-scale rechargeable lithium battery technology is to produce devices that resist combustion when subjected to mechanical or electrical stress. In practice this means the design and use on non-volatile and non-flammable electrolytes. Polymers are inherently non-volatile, but most polymers are poor solvents for lithium salts and are inadequate ionic conductors. Most classical organic polymers are also flammable. Attempts to bypass these problems by the addition of organic solvent plasticizers serves to increase the combustibility.We have designed, synthesized, and studied a range of high polymeric lithium ion conductors that are inherently less combustible than their classical organic polymer counterparts. They are based on the polyphosphazene platform in which the polymer backbone consists of a long sequence of alternating phosphorus and nitrogen atoms, with two etheric side groups attached to each phosphorus. The inorganic backbone in these polymers is non-flammable and can confer fire-resistance to the adjacent organic side units. When plasticizers are needed, small-molecule phosphazenes serve this purpose efficiently. Recent work has focused on the use of these polymers in both lithium batteries and dye-based solar cells, with conductivity, ion transport mechanism, and fire-resistance being the properties of interest.
9:30 AM - **FF1.2
Advances in Proton Exchange Membrane for Fuel Cells.
James McGrath 1 , Gwangsu Byun 1 , Ruilan Guo 1 , Ozma Lane 1 , KwanSoo Lee 1 , Myoungbae Lee 1 , Jeffrey Mecham 1 , Chang Hyun Lee 1
1 Department of Chemistry, Virginia Polytechnic Institute and State University, Blacksburg, Virginia, United States
Show AbstractAbout ten years ago we devised routes to prepare disulfonated poly(arylene ether) random copolymers, which became known as 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. However, more recently we have been investigating block copolymers. The co-continuous morphology illustrated by TEM allows for enhanced water absorption coefficients and increased conductivity. Several block copolymers were investigated and compared with random copolymer controls and various forms of Nafion. Water uptake increased with block length, and one can increase the self-diffusion coefficient of water for the block copolymers relative to the random copolymers. It also demonstrated significantly higher values than Nafion 112 or 211. The states of water in those ion-containing multiblocks are influential in defining precise morphological forms. The block continually display higher conductivity than the random copolymers. At the same time, 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. Our work has shown that the nanophase separation increases with block length, and the nanophase separated block copolymers show higher conductivity than random systems, and indeed, even Nafion controls. The synthesis and characterization of these materials will be discussed. RELATED REFERENCES: (1) Lee, H.S.; Roy, A; Lane, O.; Dunn, S.; McGrath, James 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).
10:00 AM - FF1.3
Enhanced High-temperature Polymer Electrolyte Membrane for Fuel Cells Based on Polybenzimidazole and Ionic Liquids.
Jacob Wang 1 , Steve Hsu 1
1 Department of Materials Science and Engineering, National Cheng-Kung University, Tainan Taiwan
Show AbstractAs the requirement for polymer electrolyte membrane fuel cells (PEMFC) used in elevated temperature condition have ascended, a high temperature endurable polymer electrolyte membrane (PEM) is needed. In the new generation of PEMFC, Polybenzimidazole (PBI) have received a lot of attention because of their high thermal stability, low methanol crossover and good mechanical properties; However, a thermal stable and non-volatile dopant should also be required to perform as the charge carrier. Recently, Ionic liquids (ILs) have attracted considerable attentions for its stability at wide temperature range in the electrochemical applications. Hence, in this study, we report the preparation and characterization of composite membranes based on a fluorine-containing PBI with an IL, 1-hexyl-3-methylimidazolium trfluoromethanesulfonate (HMI-Tf). The PBI/HMI-Tf composite membranes with different HMI-Tf concentrations have been prepared to investigate. The thermooxidative stability was studied with TGA, all of the membranes demonstrated terrific thermal properties, and indicated that the PBI/HMI-Tf composite membranes could fit the requirement for PEMFC work at higher temperatures up to 300 °C. The mechanical properties were also examined, the moduli and strength of the PBI/HMI-Tf composite membranes decreased with the addition of HMI-Tf amount. This could attribute to HMI-Tf acting as a plasticizer to make the PBI backbone more flexible. The methanol crossover test found the methanol barrier ability of the PBI/HMI-Tf composite membranes decreased with the increasing amount of HMI-Tf. The increase of methanol crossover in PBI/HMI-Tf composite membrane could be due to the increase of PBI’s free volume after HMI-Tf doping, because the HMI-Tf could decrease the intermolecular interaction forces. The ionic conductivity of the PBI/HMI-Tf composite membranes increased with both the temperature and the HMI-Tf content. The highest ionic conductivity (1.6x10-2 S/cm) could be reached at 250 °C under anhydrous condition. Through the activation energy calculation we hypothesized a mechanism that HMI-Tf may act as a strong ion carrier, and a plasticizer to increase the segmental motion of PBI chains then help more ion transfer. Although the addition of HMI-Tf resulted in a slight decrease in the methanol barrier ability and mechanical properties of the PBI membranes, but they still remained enough mechanical properties and much lower methanol permeability than the Nafion® 117 membrane to perform as a PEM. It is worth noting that the PBI/HMI-Tf composite membranes have demonstrated high conductivity and thermal stability up to 300 °C; This higher operation temperature in the PEMFC could accompany with higher CO tolerance, better reaction kinetics, and simpler water management. We foresee this new composite membrane to be a new promising polymer electrolyte membrane for fuel cells and become an attractive candidate for high-temperature polymer electrolyte membrane fuel cells.
10:15 AM - FF1.4
X-ray Scattering and Dielectric Studies of Nafion Membranes Swollen With Ionic Liquids.
Gregory Tudryn 1 , Sheng Liu 2 , Frederick Beyer 3 , Qiming Zhang 2 , Ralph Colby 1
1 Materials Science and Engineering, The Pennsylvania State University, University Park, Pennsylvania, United States, 2 Electrical Engineering, The Pennsylvania State University, University Park, Pennsylvania, United States, 3 U.S. Army Research Laboratory, Aberdeen Proving Grounds, Aberdeen, Maryland, United States
Show AbstractIncorporation of ionic liquids into ionomer membranes provides desirable thermal and ion conducting properties which extend the uses of such membranes for electroactive devices. In this study, Nafion membranes are swollen with various ionic liquids to observe the effect on morphology and ionic conduction. X-ray scattering in the q range of 0.007 to 0.35 inverse angstroms shows ion channels swell and merge as ionic liquid content is increased. Selection of high electron density ionic liquids allows the observation of this process over a broad range of loading levels. Dielectric spectroscopy is used to observe the ionic liquid conduction in the swollen membranes, as ionic liquid content and type are adjusted. This study provides fundamental correlations between the observed morphological transition and conduction mechanisms in Nafion membranes for actuators, batteries and fuel cells.
10:30 AM - FF1: Membranes
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11:00 AM - FF1.5
Self-organized Hybrid Proton Exchange Membranes Exhibiting High Ionic Conductivity.
Mihail Barboiu 1
1 , Institut Europeen des Membranes, Montpellier France
Show AbstractWe describe a proton exchange membrane (PEM) system in which the self-organization of molecular precursors generates directional proton-layers of high ionic group content in a scaffolding hydrophobic hybrid material. In particular, the use of self-assembling strategy of molecular precursors is noteworthy and as we have shown in this paper that it led to self-organized directional proton layers along hundreds of nanometers. The PEM hybrid membranes are homogeneous, flexible and show both thermal and chemical stabilities. They were surveyed for their ability to form proton-layers reaching high ionic conductivities. The simple synthesis procedure and good conductivity/methanol permeability selectivity suggest that the hybrid membranes may be promising candidates for use in DMFCs.(1) Arnal-Hérault, C.; Banu, A.; Barboiu, M.; Michau, M.; A. van der Lee, Angew. Chem. Int. Ed. 2007, 46, 4268-4272. (2) Michau, M.; Barboiu, M.; Caraballo, R.; Arnal-Hérault, C.; Perriat, P.; van der Lee, A. Chem. Eur. J. 2008, 14, 1776-1783.(3) Barboiu, M. Cerneaux, S.; van der Lee, A.; Vaughan, G. J. Am. Chem. Soc. 2004, 126, 3545-3550(4) Michau, M.; Barboiu, M . J. Mater. Chem. Soc. 2004, 19, 6124-6131. (Back Cover)
11:15 AM - FF1.6
Nafion: Interfacial Structure and Hydration.
Maria Bass 1 2 , Viatcheslav Freger 1 2
1 Zuckerberg Institute for Water Research, Ben-Gurion University, Sde-Boqer 84990 Israel, 2 Department of Biotechnology and Environmental Engineering, Ben-Gurion University, Beer-Sheva Israel
Show AbstractNafion is widely used as an ion-selective barrier in fuel cells. The ionic conductivity of Nafion is known to strongly depend on its hydration, thereby the thermodynamic potential and flow of water have to be thoroughly managed in fuel cells. However, a few long-debated controversies complicate Nafion hydration, such as dependence on pretreatment history and so-called Schroeder’s paradox, i.e., different hydration in vapor and liquid. Recently, we proposed a thermodynamic model of ionomer hydration (V. Freger, J. Phys. Chem. B, 2009, 113, 24) that offers an explanation of Schroeder’s paradox by showing that the external surface of solid Nafion could adopt different equilibrium or quasi-equilibrium conformations in liquid and vapor. Since the conformational changes do not necessarily propagate to the bulk due to high transient rigidity of the Nafion matrix, the inner bulk might be under different pressures depending on the external phase.Motivated by these predictions, we examined the state of Nafion at the surface using contact angle, grazing incidence small angle X-ray diffraction (GISAXS) and AFM. Contact angle measurements in vapor and liquid directly showed a drastic change from surface hydrophobicily in vapor (92 degrees) to hydrophilicity in water (27.5). GISAXS allowed an insight into the structural re-arrangements that accompany such transition. Thus GISAXS indicates that vapor environment promotes preferential alignment of the hydrophobic backbone chains in surface region burying the hydrophilic species under the surface. On the other hand, in liquid the Nafion surface apparently breaks up to randomly oriented separate normal-type micelles anchored to the surface thus fully exposing the hydrophilic groups. The transition, driven by the interfacial tensions involved in either case, is also accompanied by surface roughening well seen in AFM topographic images. These results appear to be consistent with the model and suggest that non-equilibrium surface conformations stabilized by interfacial forces may be responsible for the extra pressure exerted on the inner bulk of Nafion hence its (transient) lower hydration in vapor, as compared to liquid equilibration
11:30 AM - **FF1.7
Protic Ionic Liquid/Polyimide Hybrid Membrane for Polymer Electrolyte Fuel Cell Under Non-humidified Conditions.
Masayoshi Watanabe 1
1 , Yokohama National University, Yokohama Japan
Show AbstractThe development of novel proton-conducting materials with little or no dependence on humidity in a wide temperature range, especially at temperatures above 100 °C, remains an important challenge to the realization of practical fuel cells. We have shown that certain protic ionic liquids (PILs), composed of Brønsted acids and bases, support active hydrogen oxidation reactions and oxygen reduction reactions under entirely non-humid conditions even at temperatures higher than 100 °C, which opens up the possibility of their use as intermediate temperature fuel cell electrolytes. Furthermore, the ionic liquid electrolytes can be processed into electrolyte membranes by their hybridization with polymers, which would offer the practical utility in fuel cells. It was recently found that diethylmethylammonium trifluoromethanesulfonate, [dema][TfO], has superior characteristics as fuel cell electrolyte among more than 80 different PILs. In this work, we explored electrochemical properties of [dema][TfO] in detail and succeeded in fabricating hybrid membranes including [dema][TfO] in order to apply [dema][TfO] to an electrolyte of non-humidified medium temperature fuel cells. We focused on sulfonated polyimides as polymer matrix due to its thermal stability, film forming ability, and wide variety of molecular design. The results of fuel cell tests using the hybrid membranes will be presented in detail under different conditions.
12:00 PM - **FF1.8
Membrane Shorting: The Forgotten Fuel Cell Failure Mode.
Yeh-Hung Lai 1 , Craig Gittleman 1
1 , General Motors, Honeoye Falls, New York, United States
Show AbstractOne of the key challenges facing the commercialization of fuel cells is developing membrane electrode assemblies (MEAs) that can meet industry durability targets. Proton exchange membranes (PEMs) are the most promising membranes for automotive applications because of their relatively high proton conductivity at low temperatures. These membranes serve to conduct protons from the anode electrode to the cathode electrode of the fuel cell while simultaneously insulating electronic current from passing across the membrane and preventing crossover of the reactant gases, H2 and O2. There are three critical membrane degradation mechanisms that can lead to failure of polymer electrolyte fuel cell systems: chemical degradation, mechanical degradation, and membrane shorting. While there have been significant efforts to understand the underlying mechanisms and to develop mitigation strategies for both chemical and mechanical degradation, failure by membrane shorting has been mostly ignored.Ohmic shorting through the membrane has been identified as one of the major failure modes in PEM fuel cell systems. Shorting occurs when electrons flow directly from the anode to the cathode instead of through the device being powered. Ohmic shorting not only can reduce the performance of fuel cells, but also lead to local heat generation in the vicinity of the short, causing membrane damage that can ultimately result in gas crossover failure in fuel cells. Several challenges exist in the study of PEM shorting failure: the extremely localized shorting sites are very difficult to find; when found, the shorting morphology is often lost because of the destructive postmortem process; and the shorting failures are often accompanied and obscured by other failure modes such as membrane melting, thinning and pinholes that are more visible in the postmortem analyses.PEM failure caused by shorting is a two step process during which “soft shorts” are initially created by penetration of conductive materials, such as carbon fibers, though the thickness of the membrane. “Soft shorts” become “hard shorts” when there is a voltage excursion that leads to high local temperatures and subsequent thermal decay of the PEM. These “hard shorts” are the severe events that lead to fuel cell stack failure. Results and analysis suggest that the PEM type is not the limiting factor in preventing membrane shorting, and that mitigation is best achieved by a combination of design and operating strategies. This talk will cover the accelerated stress tests and in-situ diagnostics developed at General Motors to investigate membrane shorting, finite element modeling showing how shorts can lead to thermal runaway causing membrane thermal decomposition, and a discussion of effective mechanisms for minimizing the risk of shorting.
12:30 PM - FF1.9
Microstructure and Performance of Palladium-modified Nafion Membranes.
Xuan Cheng 1 2 , Lu Zhang 1 , Ying Zhang 1 2 , Fang-Bor Weng 3 , Chinbay Q. Fan 4
1 Materials Science and Engineering, Xiamen University, Xiamen , Fujian, China, 2 Fujian Key Laboratory of Advanced Materials, Xiamen University, Xiamen , Fujian, China, 3 Fuel Cell Center, Yuanze University, Tao-Yuan , Taiwan, China, 4 , Gas Technology Institute, Des Plaines , Illinois, United States
Show AbstractCommercially available Nafion membranes have good proton conductivity and chemical stability with a drawback of methanol crossover which adversely influences fuel cell performance. Modifications of Nafion membranes with palladium foils, thin films or coatings showed very promising in the mitigation of methanol crossover with sufficient permeability for hydrogen. Little information is available in correlation of microstructure and performance of the palladium-modified Nafion membranes under direct methanol fuel cell conditions. In this work, a series of membranes were prepared by immersing the Nafion 112 membranes into PdCl2 solutions followed by reduction in NaBH4 solutions. The palladium-modified membranes were characterized before and after the durability test in a single cell by X-ray diffraction (XRD), high resolution transmission electron microscope (HRTEM), selected area electron diffraction (SAED) and scanning transmission electron microscope (STEM) to observe the microstructure changes of Pd particles. The energy dispersive X-ray spectroscopy (EDS) and X-ray photoelectron spectroscopy (XPS) were used to analyze the composition changes of Pd particles. By comparison in the conductivities, physical and chemical properties of membranes, as well as the single cell performance, before and after the palladium modifications, the microstructure of membranes will be discussed in relation to the stability and performance of membranes.
12:45 PM - FF1.10
The Use of Superacidic Inorganic Moieties for the Promotion of Proton Conductivity.
Andrew Herring 1 , Gregory Schlichting 1 , Mei-chen Kuo 1 , James Horan 1 , Matthew Frey 2 , Hui Ren 2 , Steven Hamrock 3
1 Departmment of Chemical Engineering, Colorado School of Mines, Golden, Colorado, United States, 2 Fuel Cell components Group, 3M, St. paul, Minnesota, United States, 3 Corporate maaterials research laboratory, 3M, St. paul, Minnesota, United States
Show AbstractWe have shown that the heteropoly acids when functionalized with vinyl groups may e copolymerized with acrylates to produce films with very high protonic conduction under relatively hot and dry conditions. Morphological investigations of these materials show that the inorganic moieties cluster into phases tat are up to 1 micron in diameter. While PFGSE NMR measurements show fast diffusion on short diffusion lengths, long range diffusion is inhibited by the morphology of the films. To counter this effect we are producing similar films using super acidic inorganic moieties that do not hydrogen bond to form clusters. A full morphological description of both films will be given together with a discussion of the mode of proton transport.
Tuesday PM, April 06, 2010
Room 3005 (Moscone West)
2:30 PM - FF2.1
Thermomechanical Reliability of Proton Exchange Membranes.
Ruiliang Jia 1 , Takuya Hasegawa 2 , Jiping Ye 3 , Reinhold Dauskardt 1
1 Materials Science and Engineering, Stanford University, Stanford, California, United States, 2 Nissan Research Center, Nissan Motor Co., Ltd., Yokosuka Japan, 3 Research Department, NISSAN ARC LTD., Yokosuka Japan
Show AbstractNafion perfluorosulfonic acid (PFSA) polymer membranes are widely used as the electrolyte thin films to transport protons in PEM fuel cells. A common failure mode that limits the operational life of fuel cells involves the fracture of the membranes. This process includes the initial formation of damage in the form of pinholes and the subsequent formation and growth of cracks. In the present work, we describe a number of thin film testing methods to assess the mechanical and fracture properties of PFSA membranes under simulated fuel cell operational environments. The role of the PFSA molecular structure together with selected composite forms made with the addition of nanosize oxide (TiO2, ZrO2, etc) particles on mechanical and fracture behavior is demonstrated. The study not only reveals significant factors that influence the mechanical behavior and fracture properties of PFSA membranes in operation, such as water content, foreign cation contamination and chemical attack by peroxide radicals, but also investigates methods to improve thermomechanical reliability for fuel cell applications.
2:45 PM - FF2.2
DOE Development of Advanced Membranes for Fuel Cell Applications.
Jacob Spendelow 1 , Nancy Garland 1 , Kathi Epping Martin 1 , Donna Ho 1 , Jason Marcinkoski 1 , Dimitrios Papageorgopoulos 1
1 , DOE, Washington, District of Columbia, United States
Show AbstractThe US Department of Energy Fuel Cell Technologies Program supports research, development, and demonstration of fuel cell technologies for stationary/backup power, transportation applications, and specialty markets such as materials handling. The Program also supports activities that assist the growth of early markets to overcome critical path barriers to commercialization, including achieving significant cost reductions through economies of scale.In recent years, the FCT program has been heavily involved in development of new polymer electrolyte membranes (PEMs) capable of operating with good performance and durability under hot and dry conditions. Expansion of the operating temperature and humidity range to include hotter and drier conditions would facilitate development of fuel cell systems with increased power density, improved catalyst performance, decreased system complexity, simplified waste heat removal, improved impurity tolerance, and reduced system cost. In 2009, several novel PEMs produced by DOE-funded researchers met the DOE conductivity milestone of 0.1 S/cm at 120 °C and 50% RH. Strategies used to maintain high conductivity at low humidity included incorporation of low equivalent weight perfluorosulfonic acid materials, addition of water-retaining additives, addition of proton-conducting additives, copolymerization of heteropolyacids, and tailoring of pore structure to preserve proton-conducting pathways. Further development of these novel membrane materials, as well as optimization of MEAs based on the new materials, will be described.
3:00 PM - **FF2.3
Development and Stability of Morphological Features in Proton Exchange Membrane Materials for Fuel Cell Applications.
Robert Moore 1 , Jong Keun Park 1 , Angela Osborn 1 , Gilles Divoux 1
1 , Virginia Polytechnic Institute and State University, Blacksburg, Virginia, United States
Show AbstractOver the last several decades, perfluorosulfonate ionomers (e.g., PFSAs such as Nafion®) have become the “benchmark” membrane material for proton exchange membrane fuel cells (PEMFCs). While this unique ionomer has yielded significant commercial success, the fundamental morphology-property relationships that govern the chemical and physical properties of this complex, nanostructured polymer have been poorly understood. Despite years of investigation, it is remarkable that we know very little about the detailed structure of PFSA crystallites or the spatial arrangement of these ordered features with respect to the proximity of the ionic domains. Moreover, our understanding of the development of the crystalline phase during membrane processing is virtually non-existent, and from a current technological point of view, we know even less about the impact of crystallinity on the critical membrane properties, performance, and durability in PEMFC applications. This study involves the systematic control of the “other” important morphological feature in perfluorosulfonate ionomer (PFSA) membranes, namely the crystalline domains. While the vast majority of studies of these materials have focused on the proton-transporting ionic domains, the first topic of this presentation will highlight the critical significance of the crystalline component. As an alternative to the benchmark PFSA materials, new membrane materials are emerging based on a variety of polymer backbone chemistries, chain architectures, and chemical compositions. Morphological order and/or complexity in these new systems has been shown to vary widely, over many length scales, ranging from nanometer-scale block copolymer phase separation to micron-scale domains in membranes composed of polymer blends. In this second topic, chemical and physical considerations regarding morphological development and morphological stability in ionomer/PVDF blends and segmented multiblock copolymers will be addressed. Finally, for both topics, morphology-property/PEMFC performance relationships will be explored.
3:30 PM - **FF2.4
Nanofiber Composite Fuel Cell Membranes.
Jason Ballengee 1 , Peter Pintauro 1 , Jonghyun Choi 2 , Ryszard Wycisk 2 , Kyung Min Lee 2
1 Department of Chemical and Biomolecular Engineering, Vanderbilt University, Nashville, Tennessee, United States, 2 Department of Chemical Engineering, Case Western Reserve University, Cleveland, Ohio, United States
Show AbstractThere is an ever-increasing need for high performance polymeric ion-exchange membranes for hydrogen/air and direct methanol proton exchange membrane (PEM) fuel cells. Such new membranes must possess the requisite transport properties (e.g., high proton conductivity, low gas permeability, etc.) and have outstanding durability (i.e., enhanced mechanical, chemical, and thermal stability). Historically, the general strategy for developing new membranes for electrochemical applications has focused on: (1) the synthesis of new polymers with a high ion-exchange capacity and improved selectivity, (2) block copolymers which self assemble into nano-phase domains, (3) combining the desirable properties of two different polymers in a single membrane by blending the polymers prior to membrane casting, and (4) impregnating a functional polymer into a microporous inert support, where the support provides mechanical properties that the functional polymer does not possess. There have been some successes with these approaches, but they all have limitations. An alternate approach is to electrospin distinct nanofibers of two or more polymers from separate spinnerets and then process the resulting composite nanofiber mat into a phase separated and fully dense membrane. Thus, one can electrospin a mat containing nanofibers of Nafion® perfluorosulfonic acid polymer and uncharged. Appropriate follow-on processing will result in either a Nafion film with a reinforcing mat of polysulfone nanofibers or a network of Nafion nanofibers that is surrounded by inert and uncharged polysulfone. Both membrane configurations will be discussed, along with their properties and suitability for use in a PEM fuel cell.
4:00 PM - FF2: Membranes
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4:30 PM - FF2.5
Correlation between Morphology, Water Uptake, and Proton Conductivity in Radiation Grafted Proton Exchange Membranes.
Sandor Balog 1 , Urs Gasser 1 4 , Kell Mortensen 2 , Lorenz Gubler 3 , Hicham Ben Youcef 3 , Guenther Scherer 3
1 Laboratory for Neutron Scattering, ETH Zürich & Paul Scherrer Institut, Villigen Switzerland, 4 Adolphe Merkle Institute, University of Fribourg, Fribourg Switzerland, 2 Department of Natural Sciences, University of Copenhagen, Copenhagen Denmark, 3 Electrochemistry Laboratory, Paul Scherrer Institut, Villigen Switzerland
Show AbstractWe present small-angle neutron scattering studies of fully hydrated proton exchange membranes. Our membranes were synthesized by radiation-induced grafting of poly(ethylene-alt-tetrafluoroethylene) (ETFE) with styrene in the presence of crosslinker (divinylbenzene, DVB), and by sulfonating the polystyrene subsequently. To understand the relationship between morphology, water uptake, and proton conductivity, we applied the technique of contrast variation. We find that the membranes are separated into two phases, mostly following the morphology already defined in the semi-crystalline ETFE base film. The amorphous phase hosts the water and swells upon hydration. Swelling is found inversely proportional to the crosslinking level. Hydration and proton conductivity exhibit linear dependence on swelling. The relationship between proton conductivity and total volumetric fraction of water follows a power law, which indicates a percolated and most likely random network of finely dispersed aqueous pores in the hydrophilic domains.
4:45 PM - FF2.6
Microstructure of Gas Diffusion Layers for PEM Fuel Cells.
Nishith Parikh 1 , Jeffery Allen 1 , Reza Yassar 1
1 Mechanical Engineering, Michigan Technological University, Houghton, Michigan, United States
Show AbstractThe Gas Diffusion Layer (GDL) is a conductive and porous material interposed between the catalyst layer and the bipolar plates. Desirable functions of an ideal GDL include effectively transporting the reactant gas to the catalyst layer and removing liquid water to the gas channels, conducting electrons with low resistance, and having a low contact resistance at the various interfaces. In order to design reliable and durable fuel cells, knowledge of the GDL microstructure is necessary. Currently, the characterizations of GDLs are mostly based on porosity measurements, and the pore size distribution is considered to be the major factor affecting the fuel cell performance. Here, we studied the microstructure of GDLs manufactured by three different vendors (Toray, SGL, and Freudenberg) and the corresponding current density and voltage behaviors were recorded. Microstructure of GDL samples were imaged using field emission scanning electron microscopy (SEM). Statistical data on microstructural features including size, shape, orientation, and nearest-distance distributions of the pores were obtained by developing an in-house image analysis code in MATLAB. We found that this statistical information of GDL microstructure pores can impact the overall performance of a fuel cell.
5:00 PM - FF2.7
DFT Modeling of Ionomer Exchange Group Solvation Water Structure.
Matthew Webber 1 , Adam Yakaboski 1 , Eugene Smotkin 1
1 Chemistry and Chemical Biology, Northeastern University, Boston, Massachusetts, United States
Show AbstractNafion is commonly used as a proton exchange membrane in fuel cells. Understanding exchange group solvation is underpinning to the generation of first order models that can be refined by density functional theory(DFT). This study focused on the Nafion side chain and triflic acid (CF3SO3H) at various states of hydration. The metric for success was nearness to reproduction of the FTIR spectra of hydrated Nafion. The methodology involved maintenance of the local symmetries of the functional groups affected by hydration (i.e. C(3v) symmetry for SO3- and -CF3, C(2v) for ether linkages, etc.) while building up the hydration models. DFT results are correlated with experimental FTIR results obtained in the same lab.
5:15 PM - FF2.8
Interfacial Nanostructures of Nafion on Nanoporous Glasses having Controlled Surface Energy.
Sangcheol Kim 1 , Joseph Dura 2 , Kirt Page 1 , Hyun Wook Ro 1 , Christopher Soles 1
1 Polymers Division, National Institute of Standards and Technology, Gaithersburg, Maryland, United States, 2 Center for Neutron Research, National Institute of Standards and Technology, Gaithersburg, Maryland, United States
Show AbstractFuel cells based on polymer electrolyte membranes (PEM) show promise for a wide range of applications both in the transportation sector and for stationary power production due to their low operating temperatures. As the devices are assembled with multiple heterogeneous materials, it is increasingly important to understand and control the interfaces due to higher risks that the dissimilarity between heterogeneous materials may increase failure at the interfaces before the breakdown of bulk materials. Nafion is a commercially available fluorocarbon-based polymer and one of the most suitable PEM materials for operation at high humidity between metal electrodes. Although many models have been presented to describe bulk structures in Nafion, the interfacial structures at the boundaries of the PEM have received less attention. Interfaces between Nafion and additives also potentially improve hydration of Nafion, particularly at higher operating temperatures. Recent molecular dynamic simulations indicate the presence of local maxima in the water density near interfaces between Nafion and supporting solid surfaces.3 We also observed that lamellar structures consisting of thin alternating water rich and Nafion rich layers exist at the interface between SiO2 and the hydrated Nafion film. Unlike the water channels developed in the bulk Nafion film, the multilayers of alternating water rich and Nafion rich layers are aligned parallel with the substrate. It indicates the possible preferential wetting of hydrated Nafion film on the substrate. Thus, we investigated the interface structures in Nafion on substrates with varying surface energy ranging from hydrophilic to hydrophobic. Poly(methylsilsesquioxane) (PMSQ) spin-on organosilicate glasses (OSGs) were cast on Si wafer, cured and treated by UV-ozone (UVO) to vary the surface energy. PMSQ have inherently low dielectric constants (k = 2.7 to 2.9) in their nonporous form, can be rendered porous through the addition of a sacrificial pore generating material, and exhibit thermal stability up to 500 °C. The surface properties of the PMSQ OSGs were characterized by measuring water contact angle and using X-photoelectron spectroscopy. Diluted dispersion of Nafion were spin-cast on the PMSQ OSGs and annealed in vacuum. Neutron reflectivity was performed in the hydrated environment by simultaneously controlling sample temperature and the dew point. A vacuum environment was used to investigate the dehydration of the Nafion films. The interfacial lamellar structures were observed on the hydrophilic surface when the film was fully hydrated. As the film was dehydrated, the alternating water-rich and Nafion-rich layers disappeared. The multilayer lamellae were not induced on the hydrophobic surface.
Symposium Organizers
Andrew M. Herring Colorado School of Mines
John B. Kerr Lawrence Berkeley National Laboratory
Steven J. Hamrock 3M Fuel Cell Components Program
Thomas A. Zawodzinski Case Western Reserve University
Wednesday AM, April 07, 2010
Room 3005 (Moscone West)
9:30 AM - FF3.1
Possible Origin of Life and a New Energy Source for Life between Mica Sheets.
Helen Hansma 1
1 Department of Physics, University of California at Santa Barbara, Santa Barbara, California, United States
Show AbstractThe mica hypothesis presents a new energy device for the origins of life. In this hypothesis, simple mechanical energy – work – was a significant form of energy for making (and breaking) covalent bonds, altering the conformations of polmers and polymer aggregates, and blebbing off daughter cells form the earliest protocells.Many problems with the origin of life are solved by the hypothesis that life emerged between mica sheets. Ancient natural “books” of mica sheets provided secure nano-environments, endless energy sources, confinement chemistry effects, huge entropy reductions, and grids of anionic mineral sites bridged by exchangeable potassium ions (K+). The following scenario is proposed:Simple mechanical Work provided energy for covalent bond formation by mechanochemistry. Solar energy cycles and water movements powered up-and-down movements of mica sheets. A carbon-carbon bond’s energy at room temperature is comparable to 6 nanoNewtons of force, moving 1 Angstrom in distance. Mica’s up-and-down movements pressed on protocells, blebbing off ‘daughter’ protocells. Blebbing-off has been observed in wall-less L-form bacteria and is proposed to be a remnant of the earliest cell divisions (Leaver, Nature09).Fluid percolated into and out of spaces between mica sheets, providing cycles of wetting and drying that favor the polymerization of amino acids. The discovery of Intrinsically Disordered Proteins (IDP) turns the protein structure-function dogma upside down, because individual IDPs can assume many structures and perform many functions (Dunker, JMolecGraphicsModelling 2001). Prebiotic peptides, crowded at the edges of mica sheets, could have had simple functions.
9:45 AM - FF3.2
Effect of Li3+ Ion Irradiation on Ionic Transport Properties of Complexed Polymer Electrolytes.
Prem Gupta 1 , Govind Prajapati 1 , Rupesh Roshan 1
1 Physics, Banaras Hindu University, Varanasi, Uttar Pradesh, India
Show AbstractSwift heavy ion (SHI) irradiation effects on ionic conduction in the PVA-H3PO4 polymer electrolyte films have been investigated due to its large number of applications in electrochemical devices. Polymer electrolytes films are irradiated with 50 MeV Li3+ ions having four different fluences viz. 5x1010, 1011, 5x1011and 1012ions/cm2. XRD results show a decrease in crystallinity of the irradiated thin films at lower fluences (~5x1011) whereas at high fluence (1012), it increases. FTIR spectra suggest chain scission at low fluence and cross linking at higher fluence. Irradiation of the polymer electrolyte films with swift heavy ions shows enhancement in conductivity at lower fluences and decrease in conductivity at higher fluences. It appears that below the critical fluence, swift heavy ion irradiation increases Li+ ion diffusivity in the polymer electrolyte which provides larger pathways for ionic transport throughout the system. The temperature dependence of electrical conductivity variation has been used to compute the activation energy involved in conduction process. The ionic transference number for pristine and irradiated polymer electrolyte films has been found to be nearly unity which strongly confirms the ionic nature of the electrolyte samples.
10:00 AM - **FF3.3
Molecular Mobility and Ion Conduction in Polyester Copolymer Single Ion Conductors.
James Runt 1 , Daniel Fragiadakis 1 , Shichen Dou 1 , Ralph Colby 1
1 Materials Science & Eng, Penn State University, University Park, Pennsylvania, United States
Show AbstractIn this presentation we review the findings of our recent investigations of segmental and local dynamics, as well as ion transport, in a series of model poly(ethylene oxide)-based ionomers using dielectric spectroscopy [1, 2]. We observe a slowing down of segmental dynamics and an increase in glass transition temperature above a critical ion content, as well as the appearance of an additional relaxation process associated with rotation of ion pairs. Conductivity is strongly coupled to segmental relaxation. For a fixed segmental relaxation frequency, molar conductivity increases with increasing ion content. A physical model of electrode polarization is used to separate ionic conductivity into the contributions of mobile ion concentration and ion mobility, and a model for the conduction mechanism involving transient triple ions is proposed to rationalize the behavior of these quantities as a function of ion content and the measured dielectric constant. Our findings are compared with those from measurements on identical materials using Fourier transform infrared spectroscopy [3], quasi elastic neutron scattering, and solid state NMR. [1] D. Fragiadakis et al, J Chem. Phys 130, 064907 (2009). [2] D. Fragiadakis et al, Macromolecules 41, 5723 (2008). [3] Lu et al, Macromolecules 42, 6581 (2009). This research was supported by the Department of Energy, Office of Basic Energy Sciences, Grant No. DE-FG02-07ER46409.
10:30 AM - FF3.4
Mechanical Testing of Lithium Polymer Batteries: Implications for Flexible Batteries.
Christina Peabody 1 , Craig Arnold 1
1 Mechanical and Aerospace Engineering, Princeton University, Princeton, New Jersey, United States
Show AbstractBecause of their high energy densities and high working voltages, lithium-ion batteries are the most suitable choice for many of today’s portable electronic devices. However, trends in electronic device technology, particularly in the fields of large area and flexible electronics, are creating a need for new types of mechanically flexible energy storage devices where not only are the well-studied electrochemical properties of these materials important, but their mechanical properties are important as well. In this work, we look at how external compressive stress is accommodated by the various components (electrodes and polymer separators) of a lithium-polymer battery. Particularly, we measure the viscoelastic strain response of the battery under both cyclic and static applied loading. Preliminary results show an increase in strain with time which can be fit with a modified Kelvin-Voight model. The data fits return elastic modulus values on the order of 1 GPa and dynamic viscosities on the order of 1013 Poise for the viscoelastic material. These values correlate well with known values for the polymeric materials commonly used as separators for lithium-polymer batteries and further experiments on the separator material confirm these results. Finally, we will discuss how these results apply to more complicated stress states which may arise in flexible batteries and how static and cyclic compressive loading affects battery performance during electrochemical cycling. This work supported by ONR and NSF.
10:45 AM - FF3.5
Nanoscale Thermal Mechanical Analysis of Membrane Barrier Layers.
Dae Up Ahn 2 , Yifu Ding 2 , Virginia Ferguson 2 , Alan Greenberg 2 , Richard Noble 3 , Kevin Kjoller 1 , Craig Prater 1
2 Mechanical Engineering, University of Colorado, Boulder, Colorado, United States, 3 Chemical and Biological Engineering, University of Colorado, Boulder, Colorado, United States, 1 , Anasys Instruments, Santa Barbara, California, United States
Show AbstractAs new and more complex materials structures are employed to optimize membrane performance, the ability to fully characterize the physical and mechanical properties of the ultrathin barrier layers that comprise the critical structural element of composite membranes remains an ongoing challenge. An endemic problem with polyamide thin-film composite (TFC) membranes formed from the aramids is degradation owing to attack by chlorine and other agents used to minimize biofouling. Research to address this problem has focused either on developing chlorine-resistant membranes or using alternative agents to mitigate the biofouling. There is currently no characterization protocol for assessing the stability of polyamide membrane materials in response to the various cleaning methods and agents. Unfortunately the interfacially polymerized (IP) polyamide barrier layer is difficult to study experimentally because the functional layer is thin, highly cross-linked, and insoluble, thus precluding the use of conventional mass or spectrographic analyses. The primary tools for studying IP films such as ATR-FTIR and SEM do not permit real-time analysis of changes in the IP polyamide membrane owing to exposure to cleaning agents. In addition, conventional mechanical analysis techniques are not sufficiently sensitive for assessing changes in the IP barrier layer. The aforementioned characterization difficulties related to in-situ measurement of ultrathin film properties can be addressed using a newly developed nanoscale thermal mechanical analysis (Nano-TMA) to systematically examine the thermal mechanical properties of commercial polyamide TFC membranes. Responses can be obtained at resolutions laterally of less than 100 nm and vertically of less than 10 nm such that the uniformity of the ultrathin layers can be quantified. The Nano-TMA technique relies on a custom atomic force microscopy (AFM) probe that is resistively heated to probe the thermal mechanical transition temperature of the contacting surface. In addition, the force-distance relationship can be employed to obtain the creep response of the thin films at isothermal temperatures of interest. We will present measurements of elastic modulus as well as the creep response on TFC membranes. Such information can provide the insight for optimized membrane performance via systematic changes in mechanical and thermal properties.
11:00 AM - FF3: Membranes
BREAK
11:30 AM - **FF3.6
Mechanisms of Ionic Tranport in Membranes for Batteries and Fuel Cells.
J. Woods Halley 1
1 Physics and Astronomy, University of Minnesota, Minneapolis, Minnesota, United States
Show AbstractIonic transport in electrolyte membranes limits performance in both battery and fuel cell membranes.The problems have been well known for years, sometimes decades, but empirical progress in solving themhas been slow. The focus here is on studies to improve understanding of transport mechanisms, whichdespite extensive study, remain in dispute in several important cases. For lithium transport in polymermembranes, I will review simulation work by ourselves and others, and contend that the original qualitativepicture by Ratner and coworkers is confirmed in many respects by recent work. It means, however, thatthe fundamental difficulty is that the transport is controlled by torsion forces in the hydrocarbon backbonewhich are extremely difficult to manipulate experimentally. Turning to possibly promising additives, I reviewrecent work on proton and lithium transport in ionic liquids, on which promising experimental results havebeen reported. The data, both from simulation and experiment, indicate nontrivial collective effects in thetransport properties which need to be sorted out to control these systems. In the case of proton transport, wereport results suggesting that high mobilities occur in acid-ionic mixtures with a common anion in mixturesnear phase separation.
12:00 PM - FF3.7
Synthesis of Porous Emulsion-templated Monoliths Based on 1-Vinyl-5-Amino-1H-Tetrazole.
Carlos Youssef 1 , Marc Birot 1 , Herve Deleuze 1
1 University of Bordeaux 1, ISM, Bordeaux France
Show AbstractPreparation of emulsion-templated microcellular monolithic polymers is a well established technique. The resulting materials, known as polyHIPEs, have found numerous applications in material chemistry. However the vast majority of the work reported so far concerns the use of hydrophobic monomers (such as styrene) engaged in water-in-oil emulsification. There are very limited published data on the use of direct emulsion to prepare polyHIPEs from hydrophilic monomers. In this work, we have studied the synthesis of a nitrogen-rich water-soluble monomer and its use to prepare rigid polyHIPEs materials from a direct emulsion. The obtained polyvinyltetrazole highly porous monoliths are expected to found applications as energetic materials or a heavy metal ions scavengers. So we have prepared new polyHIPE materials according to a two-steps approach: i)Synthesis of the monomer 1-vinyl-5-aminotetrazoleii)Its copolymerization in aqueous solution with N,N’-methylenebisacrylamide (cross-linker) as part of the external phase of a High Internal Phase Emulsion.The obtained monoliths present the open-cell morphology expected for a polyHIPE material. Different characterizations have been made by various techniques like the porosimetry with intrusion/extrusion of mercury, the scan electronic microscopy (SEM), B.E.T., etc. This kind of materials could be used as components in gas generating mixtures or as compounds for selective extraction of metals from waste electrolytes. They can also be used as reactive hyper porous polymers catalysts support or in green chemistry applications.
12:15 PM - FF3.8
Understanding the Mechanism of Ionic Conductivity in Polymer Nanocomposite Electrolytes Used in Lithium Ion Batteries.
Haleh Ardebili 1 2 , Changyu Tang 1 3 , Pulickel Ajayan 1
1 MEMS, Rice University, Houston, Texas, United States, 2 Mechanical Engineering, University of Houston, Houston, Texas, United States, 3 Polymer Science and Engineering, Sichuan University, Chengdu China
Show AbstractPolymer electrolytes offer several advantages over liquid electrolytes used in lithium ion batteries. Polymer electrolytes act as both electrolyte and separator, conform to the varying volume of electrodes during recycling, can be fabricated as thin films (especially suitable for nanobatteries), are less reactive and thermodynamically more stable towards lithium, and can provide enhanced safety. However, lithium ionic conductivity in polymers is not as high as in liquid electrolytes and therefore, has been a focus of much attention in battery research. Nanofillers have shown to improve ionic conductivity in polymer electrolytes; however, the mechanism of ionic conductivity is still under debate. Some studies show amorphous polymer segmental mobility and free volume as the dominant factors for lithium ion conductivity, while other studies demonstrate unexpectedly high ionic conductivity in semi-crystalline polymers indicating possible ion hopping mechanism through the crystalline lattice space. In this study, we propose a model of ionic conductivity mechanism by investigating the effect of polymer matrix (amorphous and semi-crystalline), nanofiller type, shape, size, and surface coating. Several polymer nanocomposite electrolytes are studied. Polymer matrixes include PEO, PVA, and SPEEK. Nanofillers vary in size, shape, and material including alumina and silica spherical nanoparticles, cloisite nanoclays, and combined clay and carbon nanotubes. The ionic conductivity models used are inspired by free volume (FV) and Vogel-Tammann-Fulcher (VTF) models.
12:30 PM - FF3.9
Poly(ethylene glycol)-based Polymer Electrolytes via Atom-Transfer Radical Polymerization for Microscale Li+ Battery Applications.
Courtney Sorrell 1 , Christopher Kolodziej 1 , Daniel Membreno 2 , Heather Maynard 1 , Bruce Dunn 2 , Sarah Tolbert 1
1 Chemistry and Biochemistry, University of California Los Angeles, Los Angeles, California, United States, 2 Materials Science and Engineering, University of California Los Angeles, Los Angeles, California, United States
Show AbstractThere is significant interest in using atom-transfer radical polymerization (ATRP) to make solid-state electrolyte separator layers for battery applications. An ideal battery separator layer is ionically conducting and electrically insulating. Poly(ethylene glycol) (PEG) polymers are ideal for battery applications because the PEG chains will form crown-like structures around Li+ ions and shuttle them through a separator without the use of plasticizer or liquid electrolyte. The specific aim for the research presented here is to use ATRP to create conformal coatings on high-aspect ratio 3-D battery electrodes. These studies include a comparison and full characterization of polymers synthesized from the monomers poly(ethylene glycol) vinyl ether (PEGVE), poly(ethylene glycol) methacrylate (PEGMA), and poly(ethylene glycol) methacrylate methyl ether (mPEGMA). These monomers are incorporated into a film using standard ATRP procedures which employ a solution initiator, such as ethyl 2-chloropropionate, and a copper (I) catalyst bound by a ligand. To encourage growth from the surface an initiator, such as chloropropionyl chloride, is bound to an electrode functionalized with aminopropyltrimethoxysilane (APTMS). The terminal amine of APTMS is substituted by the initiator which is analogous to the one used in solution. A polymer is synthesized in the solution concomitantly to the polymer growing from the surface and its length gives some indication of the size of the polymer that has grown on the surface. We can control the thickness, and thus the conductivity, of these films by changing the number of polymerization steps that each film undergoes. We have characterized films based on these PEG-polymers and the initial studies have indicated that films on flat electrode materials like indium-doped tin oxide (ITO) have ionic conductivities on the order of ~10^-3 S/cm. We believe that these studies will help develop new chemistry techniques for use in battery technology and that it will translate to 3-D architectures easily.
Wednesday PM, April 07, 2010
Room 3005 (Moscone West)
2:30 PM - FF4.1
Giant Electrical To Thermal Energy Conversion in P(VDF-TrFE)-based Polymer Ferroelectric Films.
Zdravko Kutnjak 1 , Brigita Rozic 1 , Bret Neese 2 , Sheng-guo Lu 2 , Qiming Zhang 2
1 , Jozef Stefan Institute, Ljubljana Slovenia, 2 , The Pennsylvania State University, University Park, Pennsylvania, United States
Show AbstractElectrocaloric effect has attracted recently considerable attention due to its great importance for electrical to thermal energy conversion, i.e., for application in cooling or heating devices of new generation, which would be friendlier for environment. Based on indirect measurements prediction of the existence of a giant electrocaloric effect was made recently in both PZT thin films and ferroelectric polymer thin films [1,2]. A review of recent direct measurements of the giant electrocaloric effect in P(VDF-TrFE)-based ter- and copolymer ferroelectric films will be given showing that the giant electrocaloric effect is in fact common in these systems. The relevance of the critical point proximity for the enhancement of the giant electrocaloric effect similar to the enhancement of the giant electromechanical response [3] will be discussed. [1] A.S. Mischenko, Q. Zhang, J.F. Scott, R.W. Whatmore, N.D. Mathur, Science 311,1270 (2006).[2] B. Neese, B. Chu, S.-G. Lu, Y. Wang, E. Furman, Q. M. Zhang, Science vol. 321, 821 (2008). [3] Z. Kutnjak, J. Petzelt, R. Blinc, Nature 441, 956 (2006).
2:45 PM - FF4.2
Significant Ultra-low Percolation Threshold, Enhanced Positive Temperature Coefficient Effect and Dielectric Permittivity in Polymer-based Composites with Immiscible Polymers.
Haiping Xu 1 , Nai-Ci Bing 1 , Yi-Hua Wu 1 , Dan-Dan Yang 1
1 School of Urban Development and Environmental Engineering, Shanghai Second Polytechnic University, Shanghai China
Show AbstractSignificant conductive polymer-based composites consisting of immiscible semi-crystalline polymers, polypropylene (PP) and polyvinylidene fluoride (PVDF), at different volume ratios loaded with a certain concentration of nanosized carbon black (CB) were prepared by blending and sequent hot-pressing technology. The distributing status of CB in the polymers was evaluated through the micrographs and a schematic geometrical model of the CB-PP/PVDF composite. The percolation threshold of this kind of composite is much lower than those of the individual polymers. Even more, the composite at 1/1 volume ratio of PP and PVDF displays the best conductivity among different ratios at a certain concentration of CB, and it displays an outstanding PTC effect more than five orders of magnitude, and synchronously an enhanced dielectric permittivity about 24.9 at 100 Hz. These inimitable properties may owe to the formation of PP/PVDF co-continuous phases and a double-percolation effect in the composite. The novel polymer-based composite with ultra-low percolation threshold, enhanced PTC effect, as well as the significant dielectric permittivity is promising a potential application.
3:00 PM - **FF4.3
Insight into Polymer Electrolytes for Lithium Batteries from Molecular Dynamics Simulations.
Grant Smith 1 , Oleg Borodin 1
1 Materials Science and Engineering, University of Utah, Salt Lake City, Utah, United States
Show AbstractMolecular dynamics (MD) simulations can provide valuable insight into the structure, dynamics and interfacial behavior of electrolytes for lithium batteries. I will discuss in detail mechanisms of lithium solvation and transport obtained from MD simulations for both binary polymer electrolytes and single-ion conductor polymer electrolytes in which the anion has been chemically attached to the polymer backbone. Lithium solvation and transport in polymer electrolytes will be compared with that observed in carbonate-based electrolytes. The influence of polymer structure and conformational dynamics on lithium transport will also be discussed. Finally, insights into the structure of polymer electrolytes and the desolvation of lithium at the interface with graphite will be considered.
3:30 PM - FF4.4
Understanding Ion Transport in Imidazolium-based Polymers Using Dielectric Spectroscopy.
U Hyeok Choi 1 , Wenjuan Liu 1 , Hong Chen 2 , Yuesheng Ye 2 , Yossef A. Elabd 2 , Ralph H. Colby 1
1 Materials Science and Engineering, Penn State University, University Park, Pennsylvania, United States, 2 Chemical and Biological Engineering, Drexel University, Philadelphia, Pennsylvania, United States
Show AbstractThe future use of electrical energy demands development of the next generation of batteries. Existing battery technologies have limited energy storage capacity of individual battery cells and for automotive applications are severely limited by slow ion transport. To provide the major breakthroughs, a fundamental understanding of ion transport in these complex systems must be obtained. In order to deduce the mechanism of ion conduction in ion-containing polymers, not only the conductivity needs to be measured but also the number density and mobility of conducting ions must be determined. Our group has studied the basic mechanism of ion transport in single-ion conductors. To obtain a transference number of unity, one ionic charge is covalently bonded to the polymer so that only the counterions can contribute to ion conduction. In this study, imidazolium-containing monomer was synthesized and polymerized to make a cationic homopolymer with either tetrafluoroborate (BF4), hexafluorophosphate (PF6) or bis(trifluoromethanesulfonyl)imide (TFSI) anionic counterions. These ions can associate into pairs and larger aggregates. The degree of ion pairing can be estimated from the temperature dependence of the dielectric constant and knowledge of the dipole moment of the ion pair, using the 1936 Onsager equation. Using the 1953 Macdonald model makes it possible to determine concentration and mobility of conducting counterions from analysis of electrode polarization in dielectric spectroscopy. The bis(trifluoromethanesulfonyl)imide (TFSI) counterion is far superior to the others, as it plasticizes the polymer by lowering Tg greatly. This result can be anticipated by ab initio calculations of ion pairing energy and the energy gain when two ion pairs form quadrupoles. BF4 and PF6 counterions are predicted and observed to form more quadrupoles with imidazolium polymers, raising Tg and lowering dielectric constant, relative to TFSI.
3:45 PM - FF4.5
Molecular Modeling of Water Percolation and Ionic Transport in Nafion, Hyflon and Ph-SPEEKK.
Ram Devanathan 1 , Roberto Lins 1 , Michel Dupuis 1
1 Chemical & Materials Sciences Division, Pacific Northwest National Laboratory, Richland, Washington, United States
Show AbstractWe have used classical molecular dynamics simulations to examine water networks, and the transport of water molecules and hydronium ions in Nafion, Hyflon and phenylated sulfonated poly ether ether ketone ketone (Ph-SPEEKK) membranes. The effect of hydration level and temperature on membrane nanostructure and ionic transport was systematically examined. In Nafion, water network percolation was found to occur above hydration level of λ =5. In Ph-SPEEKK, much higher hydration levels were required to achieve percolation. The superior ionic transport properties of Nafion will be discussed in terms of backbone and sidechain flexibility and the pathways for water networking. The results shed light on desirable characteristics of proton exchange membranes for fuel cells.
4:00 PM - FF4: Membranes
BREAK
4:30 PM - FF4.6
Chemical Mapping of Block Copolymer Electrolytes by Energy Filtered Spectrum Imaging in a TEM.
Frances Allen 1 2 , Masashi Watanabe 3 , Nitash Balsara 4 , Andrew Minor 1 2
1 National Center for Electron Microscopy, Lawrence Berkeley National Laboratory, Berkeley, California, United States, 2 Department of Materials Science and Engineering, University of California, Berkeley, California, United States, 3 Department of Materials Science and Engineering, Lehigh University, Bethlehem, Pennsylvania, United States, 4 Department of Chemical Engineering, University of California, Berkeley, California, United States
Show AbstractFavorable candidates for the solid electrolytes in a variety of energy-technology devices are block copolymers combining conductive, soft nanoscale channels with a hard, non-conducting glassy matrix. In this work we focus on thin films of lamellar poly(styrene-block-ethylene oxide) electrolytes prepared by spin casting from a solution of the polymer and a selected salt. We have chosen to work with a sodium salt (sodium hexafluorophosphate) motivated by the current intensified interest in sodium-ion batteries. The salt ions become solvated by the polyethylene oxide phase, which forms the conductive channels of the polymer electrolyte. The material’s rigidity is provided by the polystyrene phase.We investigate the chemical distribution in the block copolymer electrolyte by energy filtered transmission electron microscopy (EFTEM) using the technique of EFTEM spectrum imaging (EFTEM SI). In EFTEM SI a series of images measured from inelastically scattered electrons is acquired at adjacent energy positions using a small energy-selecting slit. We apply this technique to the low loss portion of the electron energy loss spectrum known as the plasmon peak range, which is relatively intense and sensitive to the chemical composition of the sample. The EFTEM SI datasets are analyzed using a combination of multivariate statistical analysis and multiple linear least squared fitting. In this way the principal components of the specimen are identified and the distribution of ions in the polymer electrolyte is revealed.Low loss EFTEM SI presents significant advantages for the quantitative analysis of polymers as compared with more conventional TEM imaging techniques and these will be discussed. In addition, we present first results from a novel experimental setup for in situ electrical biasing of polymer electrolytes in a TEM. By imaging the spatial distribution of ionic species within a block copolymer in the absence and then in the presence of an applied electric field we aim to investigate the mechanism of ion transport in these materials.
4:45 PM - FF4.7
The Hierarchical Assembly of A Bridged Silsesquioxane for Hydrogen Storage.
Kimberly Cross 1 , Yunfeng Lu 1
1 Department of Chemical and Biomolecular Engineering, University of California Los Angeles, Los Angeles, California, United States
Show AbstractHydrogen storage is dominated by pore size diameters in the sub nanometer range. A novel assembly approach is used to synthesize microporous carbon materials with the potential for high hydrogen storage capacity. The hierarchical assembly of bridged silsesquioxane building molecules (perylenediimide bridged silsesquioxane) with controlled structure at multilength scale leads to the formation of crystalline materials with ordered structure. The assembly morphology is controlled based on the solution drying rate, solvent concentration, and the perylenediimide bridged silsesquioxane concentration. Subsequent carbonization of the assembled materials turns the crystalline structure into carbon/silica nanocomposites with well-defined layer structure. Finally, silica removal leads to the formation of nanoporous carbons with uniformed sub-nanometer pores (< 1 nm). Hydrogen storage capacity was determined using excess hydrogen adsorption measurements at 77K and up to 40 bar hydrogen pressure. Initial hydrogen storage capacity measurements resulted in hydrogen uptake on the order of ~2 wt%.
5:00 PM - FF4.8
A Finite Element Method for Transient Analysis of Concurrent Large Deformation and Mass Transport in Gels.
Hanqing Jiang 1 , Jiaping Zhang 1 , Xuanhe Zhao 2 , Zhigang Suo 2
1 , Arizona State University, Tempe, Arizona, United States, 2 , Harvard University, , Cambridge, Massachusetts, United States
Show AbstractLong-chain polymers may crosslink by strong chemical bonds into a three-dimensional network. The resulting material, an elastomer, is capable of large and reversible deformation. The elastomer may imbibe a large quantity of solvents, aggregating into a gel. The solvent molecules in the gel interact by weak physical bonds and can migrate. The dual attributes of a solid and a liquid make the gel a material of choice in nature and in engineering, such as tissue engineering, drug delivery and soft MEMS.Many processes in gels involve concurrent deformation and migration. For example, a drug loaded in a gel can migrate out in response to a change in the physiological conditions (i.e., the temperature, the level of pH, or the concentration of an enzyme). The rate of the release may be modulated by the deformation of the gel. As another example, patterns of crease often appear on the surface of a swelling gel, along with many other forms of buckling. Furthermore, swelling may induce stress localization in gels, which leads to cavitation and delamination. Hydrogels with sub-millimeter size have been extensively used as valves in microfluidics due to the short swelling time and large deformation. This paper studies the concurrent deformation and migration in the gel by a finite element method. We combine the kinematics of large deformation, the conservation of the solvent molecules, the conditions of local equilibrium, and the kinetics of migration to evolve simultaneously two fields: the displacement of the network and the chemical potential of the solvent. The finite element method is demonstrated by analyzing several phenomena, such as swelling, draining and buckling. This work builds a platform to study diverse phenomena in gels with spatial and temporal complexity.
5:15 PM - FF4.9
Sol-gel Synthesis of Microporous Organic Molecular Networks for Membrane Application.
Ji-Woong Park 1 , Su-Young Moon 1 , Jae-Sung Bae 1 , Eun-Kyung Jeon 1
1 Materials Science and Engineering, Gwangju Institute of Science and Technology, Gwangju Korea (the Republic of)
Show AbstractPolymerization of rigid organic building blocks with multiple reactive functional groups yields 3-dimensional, microporous covalent organic networks that are promising structures for applications in molecular storage, separation, delivery, or catalysis. However, the organic networks produced by this method are typically intractable solids or gels; hence most research on these materials has been limited to their use as matrices for the storage of gaseous molecules. If this organic microporocity is to be exploited in a broad range of applications, it is essential to create processable organic networks. Here we demonstrate the first organic sol-gel process in which the growth of molecular networks follows a two-stage kinetics involving the fluid state of colloidal dispersions prior to the formation of bulk monolithic networks, analogous to the sol-gel synthesis of inorganic oxides. The resultant microporous organic networks are readily processable into free-standing films, coatings on solid supports, nanoparticles with desired surface-functionalities, and nanocomposites with other polymeric matrices. Various functional microporous materials may be synthesized by the sol-gel method from organic units with a variety of chemical and geometrical structures.
FF5: Poster Session
Session Chairs
Andrew Herring
Thomas Zawodzinski
Thursday AM, April 08, 2010
Salon Level (Marriott)
9:00 PM - FF5.1
Ferroelectric Polymer-ceramic Nanoparticle Composite Films for Use in the Capacitive Storage of Electrical Energy.
Tim Porter 1 , Randy Dillingham 1 , David Cornelison 1 , Andy Pierce 1 , Dana Parsons 1
1 Physics, Northern Arizona University, Flagstaff, Arizona, United States
Show AbstractThe temporary storage of electrical energy produced from intermittent sources such as solar cells, thermal solar, wind or other means is an important component of any strategy to use these energy sources as a stable, long-term and reliable source of energy production. Energy storage solutions coupled to the intermittent production of electricity may ultimately consist of large-scale farms incorporating massive, centralized storage units based on chemical, thermal, physical or other storage technologies. Other means of deploying energy storage units may be based on micro-grid technologies, using smaller-scale “micro-storage” units. Desired attributes of these micro-storage units would include high energy storage density, flexible and rapid delivery of power, low cost, low weight, low power loss, and environmentally safe components.In addition to the more well-known battery storage technologies available for micro-grids, capacitive storage also possesses many of the features that are desirable for storage of electric energy. Capacitor materials exhibiting high dielectric permittivity and breakdown strength, as well as light weight and environmental safety are most desirable. Recently, new classes of capacitor dielectric materials, consisting of ferroelectric polymer matrices containing ceramic nanoparticles have attracted renewed interest owing to their high potential energy storage, charge and discharge properties and light weight.In this study, we use novel thermal deposition techniques to synthesize films of poly(vinlyidene fluoride), or PVDF, containing nanoparticles of the ceramic titanium dioxide (TiO2). This ferroelectric polymer has shown promise as a capacitor dielectric material, and possible enhanced electrical properties when combined with ceramic nanoparticles. Many areas need to be addressed, however, with these composite systems. Dispersion of the nanoparticles within the polymer matrices must be enhanced and controlled so that severe clumping of the particles is reduced. Also, functionalization of the matrices and/or the nanoparticles must be studied and enhanced in order to maximize the dielectric properties of the composite films. Characterization of these composite films will be performed including molecular weight, chemical structure and microstructure (SFM, SEM) techniques. Measurements of film parameters such as dielectric constant and breakdown voltage will also be performed, and the dispersion of the ceramic particles within the films will be characterized. The effect of film properties on vacuum parameters, temperatures, stoichiometry and other variables will also be reported.
9:00 PM - FF5.10
Preparation of Phenol/Alumina Activated Carbon Hollow Fiber Membrane for a Volatile Organic Compounds(VOCs) Separation.
You-In Park 1 , Kyung Yong Shin 1 2 , Seung-Eun Nam 1 , Beom Sik Kim 1 , Jeong Kwon Suh 1 , Kee Kahb Koo 2
1 Environment & Resources Research Center, Korea Research Institute of Chemical Technology, Daejeon Korea (the Republic of), 2 Chemical and Biomolecular Engineering, Sogang University, Seoul Korea (the Republic of)
Show AbstractCarbon membrane materials have received considerable attention for the gas separation including hydrocarbon mixture of ingredients of the volatile organic compounds (VOCs) because they possess their higher selectivity, permeability, and stability than the polymeric membranes. The use of activated carbon membranes makes it possible to separate continuously the VOCs mixture by the selective adsorption-diffusion mechanism which the condensable components are preferentially adsorbed in to the micropores of the membrane. The activated carbon hollow fiber membranes with uniform adsorptive micropores on the wall of open pores and the surface of the membranes have been fabricated by the carbonization of a thin layer of phenolic resin deposited on porous alumina hollow fiber membrane. The use of phenolic resin as a carbon membrane precursor provides the carbon films with molecular sieve properties, a higher carbon yield, and a lower cost. Oxidation, carbonization, and activation processing variables were controlled under different conditions in order to improve the separation characteristics of the activated carbon membrane. The activated carbon membranes yielded higher separation performance for hydrocarbon mixtures such as ethane, propane, and butane composed the VOCs: hydrocarbon permeances of 103-104 GPU (1 GPU=10-6 cm3(STP)/cm2 s cmHg) and butane/nitrogen selectivity of 107, propane/nitrogen selectivity of 23, and ethane/nitrogen selectivity of 9 were measured. The activated carbon membrane show good properties for separating the hydrocarbon mixture. As the number of carbon increases, the selectivity for the activated carbon membrane sharply increases, implying that the activated membrane seems to occur by means of a combination of molecular sieving and selective adsorption-diffusion. From this study, the activated carbon hollow fiber membranes with good separation capabilities by the molecular size mechanism as well as selective adsorption on the pores surface followed by surface diffusion effective in the recovery hydrocarbons from hydrocarbon-N2 mixtures have been obtained. Therefore, these activated carbon membranes prepared in this study are shown as promising candidate membrane for separation of VOCs.
9:00 PM - FF5.11
Separation of Dimethyl Carbonate/Methanol Mixtures by Pervaporation With Crosslinked Poly(vinyl alcohol) Membranes.
You-In Park 1 , Mi Rae Seo 1 3 , Kyung Yong Shin 1 , Seung-Eun Nam 1 , Beom Sik Kim 1 , Choong Kyun Yeom 2 , Ho Bum Park 3
1 Environment & Resources Research Center, Korea Research Institute of Chemical Technology, Daejeon Korea (the Republic of), 3 , Hanyang University, Seoul Korea (the Republic of), 2 , SepraTek, Incheon Korea (the Republic of)
Show AbstractDimethyl carbonate(DMC) has attracted increasing interest in the chemical industry as an environmental benign chemical compound and unique intermediate with versatile chemical reactivity. However, in the synthesis of DMC, DMC is obtained as mixture with methanol(MeOH) due to the use of excess methanol, so separation of the azeotrope mixture with DMC at different MeOH content is an important step in DMC manufacturing. For the separation of DMC/MeOH mixtures by pervaporation, poly(vinyl alcohol)(PVA) membranes by cross-linking with glutaldehyde(GA) have been fabricated. The membranes of different GA content (PVA:GA=1/0.08, 0.12, 0.16 mol%) were characterized by Fourier transform infared spectra (FT-IR) and swelling test. The swelling degree increases with increasing the GA content, which is caused the increase of aldehyde hydrophilic group in the crosslinking reaction. The pervaporation performances of membranes were observed by permeation experiment with different composition feed solution (DMC/MeOH=30/70, 50/50, 70/30 wt %) at operation temperatures ranging from 30 to 50oC. With increasing the GA content as a crosslinking agent, the fluxes of MeOH and DMC increase but the selectivities decrease. The increasing flux results from the increasing swelling degree due to the increase of aldehyde hydrophilic group. Also, as the MeOH content of the feed solution increases, the membrane becomes more swollen and increases the free volume because the membrane materials have a stronger solubility affinity with MeOH. As a result, the fluxes increase but the selectivities decrease, which can be explained by the MeOH plasticization effect toward the membrane. As the operating temperature of feed solutions increased, the mobility of the polymer chains of membrane increase, leading permeation flux increased but selectivity decreased. The PVA/GA(=1/0.08 mol%) membranes using the feed solution of DMC/MeOH (=70/30 wt %) mixture in feed presented superior separation performance: the DMC flux of 1.35 g/m2hr, the MeOH flux of 29.98 g/m2hr, and selectivity was 51.93 at 30oC. Therefore, it could be expected that the PVA/GA membrane prepared in this study would be used for the separation of DMC/MeOH azeotrope mixtures.
9:00 PM - FF5.12
Effects of the Structure and Ion Type on the Ionic Conductivity of Imidazolium-based Polymers.
U Hyeok Choi 1 , Wenjuan Liu 1 , Minjae Lee 2 , Harry W. Gibson 2 , Ralph H. Colby 1
1 Materials Science and Engineering, Penn State University, University Park, Pennsylvania, United States, 2 Chemistry, Virginia Polytechnic Institute & State University, Blacksburg, Virginia, United States
Show AbstractWe design, synthesize and characterize ionic polymers with imidazolium cations covalently attached to the polymer chain and various ionic liquid counterions. These ionic polymers are single-ion conductors that are potentially useful for ionic actuators. An applied voltage on the polymer thin film causes accumulation and depletion of bulky anions at the anode and cathode, respectively, leading to bending actuation Our efforts have focused on polyacrylates with pendant imidazolium salt side chains. The imidazolium cations are attached to the polymers with flexible alkyl spacer chains (C4 - C12) and also have a variety of alkyl and alkyl ether chain termini. The anionic counterions are also varied; tetrafluoroborate (BF4), hexafluorophosphate (PF6) and bis(trifluoromethanesulfonyl)imide (TFSI) were mainly used in this study. Ab initio calculations estimate the dipole moment and formation energy of the imidazolium – counterion ion pair and the energy of the quadrupole formed from two ion pairs. Dielectric relaxation spectroscopy (DRS) is utilized to measure the dielectric constant and conductivity, as functions of temperature. The 1936 Onsager model is used with the measured dielectric constant and calculated pair dipole moment to estimate the fraction of ions in the isolated ion pair state. The 1953 Macdonald model is applied to estimate the number density of conducting ions and their mobility, from electrode polarization at the lowest frequencies in DRS. The results for monomers and polymers with various spacer lengths, chain termini and different counterions will be compared and allow us to present some conclusions regarding optimal design of imidazolium polymers for facile ion transport.
9:00 PM - FF5.13
Scratch Damage and Recovery of Controlled Epoxy Networks.
Hamed Lakrout 1 , Aaron Forster 2 , Lipiin Sung 2 , Chris Michaels 3 , Deborah Wang 2
1 New Products, Dow Chemical, Midland, Michigan, United States, 2 Building and Fire Research Laboratory, NIST, Gaithersburg, Maryland, United States, 3 Chemical Science and Technology Laboratory, NIST, Gaithersburg, Maryland, United States
Show AbstractSurface scratches in a series of controlled epoxy networks (CEN) were measured using a combination of instrumented indentation protocols and laser scanning confocal microscopy. Identical epoxy chemistry with increasing molecular weight between crosslinks provided different viscoelastic relaxation behaviors with the same modulus at ambient conditions. The glass transition temperatures ranged between 70 ○C and 117 ○C. The high Tg CEN exhibited the lowest penetration depth and the highest elastic recovery. The results are analyzed with respect to the macroscale bulk properties and underlying molecular architecture of the CEN materials.
9:00 PM - FF5.15
Study of Self-assembled Diblock Copolymer Thin Films for Nanoscale Electronic Devices.
James Li 1 , Oksana Protsiv 1 , Jean-Charles Eloi 2 , Ian Manners 2 , Gilbert Walker 1
1 Chemistry, University of Toronto, Toronto, Ontario, Canada, 2 Chemistry, University of Bristol, Bristol United Kingdom
Show AbstractConducting probe atomic force microscopy (CP-AFM) and electrochemical techniques are used to investigate the electronic properties of polystyrene-b-polyferrocenylsilane (PS-b-PFS) diblock copolymer thin films. In this system, cylindrical domains of polyferrocenylsilane, a weak semiconductor, are surrounded by polystyrene, an insulating material. Recently, we have utilized PS-b-PFS to demonstrate two-terminal, vertically configured nanoscale electronic elements that are self-assembled into electrically isolated regions in a thin-film configuration. In this work, a self-assembled, 2D, position-addressable device can be demonstrated is envisioned that would utilize the diblock copolymer layer as both the active and patterning element, and another self-assembled monolayer (SAM) serves as an added element to control the transport of charge.
9:00 PM - FF5.16
Ferroelectric Domain Study of the P(VDF-TrFE) Thin Film Using Angle-resolved Piezoresponse Force Microscopy.
Moonkyu Park 1 , Seungbum Hong 2 , Yoonyoung Choi 1 , Jongin Hong 3 , Kwangsoo No 1
1 Department of Materials Science and Engineering, Korea Advanced Institute of Science and Technology, Daejeon Korea (the Republic of), 2 Materials Science Division, Argonne National Laboratory, Argonne, Illinois, United States, 3 Department of Chemistry, Imperial College London, London United Kingdom
Show AbstractTo date a clear understanding of both domain configuration and polarization switching phenomena has been of significant importance in ferroelectric polymers including poly(yinylidene fluoride-trifluoroethylene), P(VDF-TrFE). Recently, we have developed angle-resolved piezoelectric force microscopy that allows for unambiguously constructing the domain configuration. In order to identify the role of polarization directions in the out-of-plane polarization reversals, we prepared P(VDF-TrFE) thin films on Au/SiO2/Si substrates by a spin-coating technique and subsequently annealed in an oven. Stable ferroelectric β-phase formation that exhibits strong ferroelectric properties was confirmed by both x-ray diffraction (XRD) and Fourier Transform infrared (FTIR) spectroscopy in the prepared sample. Then, we obtained the in/out-of- phase and amplitude signals while rotating the sample around the film surface normal with an interval of 30 o from 0 o to 180 o. Out-of-plane PFM signals were also measured while applying voltage to the sample with an interval of 0.5 V from 1 V to 10 V at each turn. Therefore, we could determine the relationship between the domain configuration and polarization switching phenomena in the sample.
9:00 PM - FF5.17
Synthesis and Characterization of Low-bandgap Bulk-heterojunction Solar Cells Based on Dialkoxynaphthalene.
Seul-Ong Kim 1 , Soon-Ki Kwon 1 , Yoon-Hi Yoon-Hi Kim 1 , Chan Eon Park 2 , Moon-Chan Hwang 1
1 , Gyeongsang National University , Jinju Korea (the Republic of), 2 , Pohang University of Science and Technology, Pohang Korea (the Republic of)
Show AbstractNew electron donor polymers with highly yield were synthesized by suzuki coupling reaction and characterized using elemental analysis, 1H-NMR, UV absorption and Cyclic Voltammetry (CV) studies. A good thermal properties of synthesized materials were confirmed by the thermogravimetric analysis(TGA) and differential scanning calorimeter(DSC). 5% weight losses of electron donor materials were observed at 343-345 oC. Solar cell devices based on the prepared materials were fabricated and tested. The observed high open circuit voltages (Voc) of devices ranging from 0.80 to 0.90 V can be attributed to lower HOMO level of electron donor materials (5.38~5.42 eV) and their low band gap. It is reported that these materials can be used for high-performance, soluble process, and large-area polymeric solar cell applications.
9:00 PM - FF5.18
Broadband Dielectric Spectroscopy and Quasi-Elastic Neutron Scattering on Plasticized Single-Ion Polymer Conductors.
Hua-Gen Peng 1 , Kirt Page 1 , Scott Eastman 1 , Chad Snyder 1 , Christopher Soles 1 , Ashoutosh Panday 2 , James Runt 2
1 Polymer Division, National Institute of Standards and Technology, Gaithersburg, Maryland, United States, 2 Materials of Science and Engineering, Pennsylania State University, University Park, Pennsylvania, United States
Show AbstractSolid polymer electrolytes generally exhibit insufficient ion conductivity to be viable for lithium ion battery technologies. Introducing additives, such as plasticizers or diluents that facilitate molecular mobility, into the polymer electrolyte is a reasonable approach for enhancing ion conductivity at room temperature. It is therefore important to develop a detailed understanding of the effect of plasticizers on the ion conduction and establish predictive correlations between the ion conductivity and local and segmental polymer dynamics. However, it is extremely difficult to understand the complicated interplay between the dynamics of the plasticizer molecules, the polymer electrolyte, and the mobile ions. To this end, we combine broadband dielectric spectroscopy (BDS) and quasi-elastic neutron scattering (QENS) measurements on a simple, single-ion model polymer electrolyte in the presence of a small molecule plasticizer. The BDS measurements are most sensitive to mobility of the species with the largest dipole moments, namely, the ion pairs. BDS is typically used to characterize the ion mobility, the characteristic ion conduction time constant, and the parameters of the polymer local beta and segmental alpha processes. QENS, on the other hand, is most sensitive to the dynamics of the hydrogenated species, not the ions. By comparing the ion dynamics from BDS to the host dynamics from QENS, we seek to better understand the mechanism of ion conduction in these materials. In addition, we utilize a deuterium-substituted plasticizer that does not contribute to the inelastic scattering appreciably. With this approach we are able to quantify how the plasticizer influence the dynamics of the polymer electrolyte, and then directly quantify the impact of this on the ion transport as measured by BDS.
9:00 PM - FF5.2
Thermal Behavior and Conductivity of Rubidium Dihydrogen Phosphate (RbH2PO4) at High Temperature.
Zikun Li 1 , Tongbor Tang 1
1 Physics, Hong Kong Baptist University, Hong Kong China
Show AbstractRbH2PO4 ionic compound has emerged as a viable electrolyte for intermediate-temperature fuel cell, and has been subjected to thermal analysis and impedance spectroscopy to clarify its high-temperature properties. A thermo-analytical peak which was identified at 127oC without any evidence of weight loss is due to structural phase transition rather than thermal decomposition. It has been observed the phase transition temperature Tp, scattering widely over the temperature range of 80 – 120oC, is relatively independent of heating rate. Impedance spectroscopy performed under dry N2 condition revealed a fast increase in conductivity at ~245oC, which is a consequence of dehydration in the heating process. Application of humidified N2 suppressed the dehydration effectively. Furthermore, it is found that a sharp jump in conductivity by several orders of magnitude appeared at ~280oC in humidified N2 atmosphere, indicative of a superprotonic phase transition. The existence of a superprotonic transition under humid condition instead of dry condition, in despite of the same sample, suggests that humidity has an important influence on conductivity for RbH2PO4 crystal.
9:00 PM - FF5.3
Preparation, Characterization and Curing Properties of Epoxy-terminated Poly(alkyl-phenylene oxide)s.
Chia-Teh Su 1 , Kun-Yu Lin 1 , Mong Liang 1
1 Applied Chemistry, National Chiayi University, Chiayi Taiwan
Show AbstractA series of dihydroxyl telechelic poly(alkyl-phenylene oxide)s (1) have been synthesized by oxidative polymerization of alkylphenols with various aromatic diols using manganese or copper amine catalysts. The novel telechelic derivatives (1) were epoxidized with epichlorohydrin yielding a series of new epoxidized poly(alkyl-phenylene oxide)s (EPPO, 2) and the structures, properties were studied by nuclear magnetic resonance spectroscopy (NMR), differential scanning calorimetry (DSC), thermo gravimetric analysis (TGA), and gel permeation chromatography (GPC). The 1:1 blends of diglycidyl ether of bisphenol-A (DGEBA) with EPPO resins were cured with three curing agents and the effects of chemical structure change on thermal property of the curing matrixes were discussed. Incorporation of EPPOs to DGEBA epoxy system resulted in a significant increase in its glass transition temperature (Tg), thermal stability and flame resistance. The Tg values and char yields arising from a DDM-cured epoxy resin are usually higher than those of dicyandiamide (DICY) or 2-methylimidazole (2-MI) analogues and the reactivity of epoxy blends with three curing agents presents an increase in the order of 2-MI, DDM, and DICY. In general, the tetramethylbisphenol-A (TMBPA)-derived polymer exhibits the lowest Tg, char yield and dielectric constant among PPO derivatives whereas the biphenol polymers usually results in higher Tg and char yield due to its rigid rod structure
9:00 PM - FF5.4
Surface Characterization of Poly(acrylic acid) Grafted to Photo-oxidized Perfluorosulfonic Acid Membrane Used in Fuel Cells.
A. Bailey 1 , F. Lu 1 , A. Khot 1 , S. Hussain 1 , K. Rugg 1 , G. Leong 1 , T. Debies 2 , G. Takacs 1
1 Chemistry, Center for Materials Science & Engineering, RIT, Rochester , New York, United States, 2 , Xerox Corporation, Webster, New York, United States
Show AbstractInternational interest in both renewable energy sources and reduction in emission levels has placed increasing attention on a number of electrochemical fuel cell devices that use ionic conducting polymer electrolyte membranes such as Nafion® which is a copolymer of tetrafluoroethylene and perfluoro[2-(fluorosulfonylethoxy)- vinyl]ether [1]. Plasma treatment is often used to modify the Nafion surface while graft polymerization allows for the possibility of chemically designing macro- and micro-systems of “shell and core” type where the core is the modified substrate and the shell is the grafted polymer.This paper reports on the surface modification of Nafion-117 using UV and vacuum UV (VUV) photo-oxidation downstream from an Ar microwave plasma and the grafting of poly(acrylic acid) to the modified surface. X-ray photoelectron spectroscopy was used to analyze the modified Nafion surface and poly(acrylic acid) grafted to the modified surface.® Nafion is a registered trademark of E. I. duPont de Nemours & Co., Wilmington, DE. 1. R. J. Press, K. S. V. Santhanam, M. J. Miri, A. Bailey and G. A. Takacs, Introduction to Hydrogen Technology, John Wiley & Sons, Inc., Hoboken, New Jersey (2009).
9:00 PM - FF5.5
Polymer Materials and Membranes for Energy Devices Effect of Nanoscale Phase Separation on the Efficiency of Polymeric Light Emitting Diodes Studied with Scanning ToF-SIMS.
Che-Hung Kuo 1 2 , Bang-Ying Yu 1 , Guo-Ji Yen 1 2 , Wei-Chun Lin 1 , Wei-Ben Wang 3 , I-Ming Lai 3 , Szu-Hsian Lee 1 2 , Wei-Lun Kao 1 2 , Chia-Yi Liu 1 , Yun-Wen You 1 , Hsun-Yun Chang 1 , Chi-Ping Liu 1 3 , Jwo-Huei Jou 3 , Jing-Jong Shyue 1 2
1 Research Center for Applied Sciences, Academia Sinica, Taipei Taiwan, 2 Materials Science and Engineering, National Taiwan University, Taipei Taiwan, 3 Research Center for Applied Sciences, National Tsing Hua University, Hsinchu Taiwan
Show AbstractOver the past two decades, organic light-emitting diodes (OLEDs) have drawn considerable attention as a potential technology for flat panel displays and lightening. There are some advantages of polymer LEDs (PLEDs) over small molecule LEDs such as the possibility of direct printing by using an inkjet printer or laser thermal transfer.In comparison to small molecule LEDs, an additional phase separation between polymer host and small molecular guest could occur when mixing molecules of significantly different chemical structures. As the result, understanding the effect of chemical structure on the nanostructure in the resulting polymer film is crucial and beneficial to PLEDs. In this work, scanning time-of-flight secondary ion mass spectrometry (ToF-SIMS) with C60+ ion sputtering is used to examine the molecular distribution inside the volume of PLEDs based on the difference in their chemical structure. Three polymeric host materials with identical energy levels are studied in this work. It is found that the degree of phase separation in different polymer hosts is different because of their difference in chemical structures. Unlike bulk heterojunction solar cell that benefits from the phase separation, the efficiency of PLED decreases with the nanostructure. Such a difference arises because solar cell requires the path formed by phase separation to remove charge carrier from the active layer while PLED needs to trap the carrier inside the active layer and the phase separation provides a path for carrier to transport without generating excitons in the host material.
9:00 PM - FF5.6
Structural Effects in Diketopyrrolopyrrole Copolymers for Transistor and Solar Cell Applications.
David Gendron 1 , Ahmed Najari 1 , Pierre-Olivier Morin 1 , Stephanie Grenier 1 , Mario Leclerc 1
1 Chemistry, Université Laval, Quebec, Quebec, Canada
Show AbstractIn recent years, conjuguted polymers have attracted more and more attention due to their growing efficiencies in photovoltaic solar cells. Many structures have been published in the past few years containing a thiophene, benzothiadiazole or thienothiophene carboxylate core to name only a few. However, the utilization of a diketopyrrolopyrrole moiety is relatively unexplored for polymeric solar cells. Our group has recently reported a copolymer using a 1,4-diketopyrrolopyrrole (DPP) core and a 2,7-carbazole (CBz) moiety. The resulting highly substituted polymer possesses good molecular weight and solubility. Preliminary characterization has shown field effect transistors with a hole mobility up to 0.02 cm2/V.s and solar cells with a power conversion efficiency of 1.6 %. To further improve these values, a study of the length of the alkyl side chains on both diketopyrrolopyrrole core and carbazole part was performed. It is useful to investigate these effects on the organisation of the polymer to eventually optimize their performances in plastic electronics.Thus, seven new polymers have been synthetized and are divided in two categories. The first category contains polymers with the same alkyl chain on both the DPP and the carbazole part and the second category includes polymers that possess differents alkyls chains on the DPP part compare to the carbazole part. The length of the alkyl side chains varies from C6H13 to C12H25. All polymers have been polymerized by a Suzuki cross-coupling polycondensation and have led to number-average molecular weights above 16 kDa and polydispersity indexes between 1.8 and 4.3. Also, it is noteworthy that the modification of the alkyl chain does not seem to influence the electronic properties. In fact, we have obtained almost the same value for the HOMO (-5.44 eV) and LUMO (-3.88 eV) energy levels with a band gap of 1.65 eV. Nevertheless, X-ray diffractions patterns done at 250°C, have shown better organisation for the polymers which possesses the same alkyl side chain on both the DPP and CBz units and with a chain length between 8 to 10 carbon atoms. Photovoltaic devices were made in air to fully evaluate the effect of the modification of the alkyl side chain. To summerize, polymers with alkyl side chain C8H17 and C10H21 have led to power conversion efficiency of 2.27 and 2.36 %, respectively. From those results, we can imply that the optimal side chains length are between 8 to 10 carbon atoms, and have a real effect on the morphology of the active layer.
9:00 PM - FF5.8
Investigation of Ferroelectric - Ceramic Nanoparticle Composite Materials Using XPS, SEM and EDX.
Randy Dillingham 1 , Tim Porter 1 , David Cornelison 1 , Dana Parsons 1 , Andrew Pierce 1
1 Physics and Astronomy, Northern Arizona University, Flagstaff, Arizona, United States
Show AbstractIn this study, novel deposition techniques are used to synthesize ferroelectric polymer - ceramic nanoparticle composite films. These materials show great promise for possible use in capacitor applications where the composite approach allows for the integration of complimentary features such as high dielectric permittivity from the integrated nanoparticles and high breakdown strength from the polymer matrix, resulting in a greatly enhanced energy density. In this particular investigation, polyvinylidene fluoride (PVDF) containing nanoparticles of the ceramic titanium dioxide have been synthesized using physical vapor deposition techniques. Results are presented concerning the composition and structure of the materials using x-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM) and energy dispersive x-ray analysis (EDX). Film parameters such as the breakdown voltage and dielectric constant, as well as the dispersion of the ceramic particles within the films will also be presented.
9:00 PM - FF5.9
Anhydrous Proton Conducting Polymer Electrolytes Based on Poly(phosphonic acid)s.
Sung-Il Lee 1 , Myeungsoo Song 1 , Dukho Kim 1 , Do Yoon 1 , Wolfgang Meyer 2 , Kirt Page 3 , Huagen Peng 3 , Christopher Soles 3
1 Chemistry, Seoul National University, Seoul Korea (the Republic of), 2 , Max Planck Institute for Polymer Research, Mainz Germany, 3 Polymer Division, National Institute of Standards and Technology, Gaithersburg, Maryland, United States
Show AbstractAnhydrous polymer electrolytes are attracting considerable attention for their potential applications in the fuel cells operation at intermediate temperatures (100~200C). In particular, phosphonic acid is regarded as an attractive protogenic group due to the high concentration of intrinsic protonic defects as a result of self-dissociation. In this work, poly(vinylbenzyloxy-alkyl-phosphonic acid)s containing phosphonic acid as side group were synthesized and the structure-property relationships were studied. Resulting polymers were characterized concerning thermal stability, the proton conductivity under anhydrous condition, the phase-separated morphology, and local chain dynamics. In addition, the polymers were mixed with basic heterocycles such as triazole and the acid-base composite materials were characterized in regards to the improvement of anhydrous proton conductivity and the responsible mechanism.
Symposium Organizers
Andrew M. Herring Colorado School of Mines
John B. Kerr Lawrence Berkeley National Laboratory
Steven J. Hamrock 3M Fuel Cell Components Program
Thomas A. Zawodzinski Case Western Reserve University
Thursday AM, April 08, 2010
Room 3005 (Moscone West)
9:30 AM - FF6.1
Theoretical and Experimental Study of Coupled Case II Diffusion and Large Deformation of Hydrogels.
Howon Lee 1 , Jiaping Zhang 2 , Xia Chunguang 1 , Hanqing Jiang 2 , Nicholas Fang 1
1 Mechanical Science and Engineering, University of Illinois at Urbana Champaign, Urbana, Illinois, United States, 2 Mechanical Engineering, Arizona State University, Tempe, Arizona, United States
Show AbstractHydrogel is a network of polymer chains which allows the diffusion of solvent in the network. Upon solvent diffusion, hydrogel undergoes significant volumetric change, often in response to environmental stimuli such as temperature and pH. This unique process has become increasingly important in many applications ranging from MEMS devices to tissue engineering and drug delivery. It is well accepted that for most glassy polymers, at temperatures far above Tg(glass transition temperature), the diffusion follows Fick’s law, where the flux increases linearly with the gradient of solvent concentration. However, near or below Tg, a non-Fikian behavior is observed. One particular instance of non-Fickian diffusion is called Case II diffusion. Because of the complex physical situation including moving interface between dry(glassy) and wet(rubbery) regions and strong coupling between solvent migration and polymer deformation, the coupled Case II diffusion and large deformation has not been fully understood. Here we present a theoretical model for Case II diffusion coupled with a large deformation of polymer. The polymer network is modelled as a viscoelastic material characterized by 3D Maxwell model in the large deformation theoretical framework. The diffusion law states that the flux depends on the gradient of solvent concentration and the viscoleasticity of the polymer, where a phenomenological relation is used to link the diffusion coefficient and the solvent concentration by following the Thomas and Windle model. Coupling between mass transport of solvent and large deformation of polymer is described by molecular incompressibility and momentum balance equation. In our experiment, porous poly(ethylene glycol) diacrylate (PEG-DA) hydrogel was synthesized by mixing PEG-DA prepolymer with PEG in a ratio of 1:3. Not being polymerized, PEG contributes to reducing crosslinking density by occupying intermolecular space between PEG-DA during photo-polymerization. In addition, this polymer dramatically changes optical property from transparent to opaque when it swells. This facilitates visualization of the interface between dry and wet regions in experiment. Viscoelastic parameters were measured using nanoindenter, and concentration dependent diffusion coefficient using magnetic resonance imaging (MRI). Flory interaction parameter was obtained from equilibrium swelling ratio. Using the parameters obtained above, numerical simulation of the model was carried out. Our result showed the presence of sharp diffusion front and its linear propagation trend, indicating Case II diffusion. In both diffusion front propagation and polymer deformation, simulation result agreed very well with 1D swelling experiment of a PEG-DA rod. We expect that our theoretical model and experimental method for Case II diffusion will help better understand the underlying physics of hydrogel behaviour and provide fundamental basis in exploration of various hydrogel applications.
9:45 AM - FF6.2
Effects of Multi-valent Ions on Polyelectrolyte Brush Behavior.
Robert Farina 1 , Matthew Tirrell 1 , Nicolas Laugel 1
1 Bioengineering, UC-Berkeley, Berkeley, California, United States
Show AbstractThis presentation will describe the behavioral and structural properties of end-tethered polyelectrolyte brushes in the presence of multi-valent and mono-valent counterions. Combining electrochemical experiments using cyclic voltammetry (CV) and surface force experiments using the surface forces apparatus (SFA), a detailed study of the amphiphilic diblock copolymer poly(t-butyl styrene)20 – poly(styrene sodium-sulfonate)420 (PtBS-PSSNa) was performed. Starting with a hydrophobic modified surface, the hydrophobic block of this copolymer is then anchored to the surface allowing this investigation to be based purely on the thermodynamic interactions of the polyelectrolyte block. Past studies have detailed polyelectrolyte brush behavior using solely mono-valent counterions providing the ground work for this current analysis using the multi-valent counterion of ruthenium hexamine and the mono-valent sodium. Through combining CV results and SFA results, all at corresponding identical ionic environments, a detailed analysis of confined ruthenium hexamine counterion charges (Q) and equilibrium brush height (L0) was made possible. Brush structure and behavior is highly dependant upon the amount of ruthenium hexamine inside the brush due to its strong affinity to replace the sodium ions as the primary counterions inside the brush. These studies were performed varying both the ionic strength and the ionic ratio (ruthenium hexamine to sodium) of the surrounding environment. As the ionic ratio increases, the brush becomes more saturated with ruthenium hexamine. Simultaneously the brush also moves towards its more entropically favored collapsed state while also developing adhesive properties, not present without multi-valent counterions, when brushes are brought together using the SFA.
10:00 AM - FF6.3
Conventional TEM vs STEM and EELS Imaging of Diblock Copolymer Systems.
Sergey Yakovlev 1 , Kenneth Downing 1 , Nitash Balsara 2 , Xin Wang 2
1 , Lawrence Berkeley National Laboratory, Berkeley, California, United States, 2 , University of California Berkeley, Berkeley, California, United States
Show AbstractFor application of membranes in fuel cells, phase separated diblock copolymers may have advantages over homogeneous polymer electrolytes due to their ordered structure which can provide continuous pathways without bottlenecks for the ions within a rigid matrix. At the same time, such materials represent more convenient object to study the structure-property relationship than homopolymers. However study of the morphology of such materials by transmission electron microscopy may be challenging due to similar scattering crossection of the phases. Here we examine the sulfonated polysterene (PSS) – polymethylbutelene (PMB) block copolymer synthesized in three steps: (1) ionic polymerization, (2) hydrogenation, and (3) sulfonation. We compare images collected by conventional TEM, HAADF STEM and low loss EELS imaging in order to evaluate the efficiency of each method for describing the phase structures. We did not use any stains, but rather relied on the contrast due to slight difference in density, chemical bonding and presence of the sulfur ions in one of the phases.To analyze the EELS data we use multiple least square fitting with the linear combination of reference spectra. The references were obtained from the experimental dataset by brute-force constrained least-squares regression. We demonstrate that while low loss EELS is able to produce images with resolution of at least 3.5 nm for our polymer system its detection efficiency is inferior to the detection efficiency of HAADF imaging. We attribute this difference to the delocalization of the Plasmon interaction, which effectively averages the signal over the two phases. This interpretation is supported by the fact that extracted references had only small differences comparing to the difference between spectra of pure PSS and PMB. HAADF STEM imaging was found to be the most effective method of polymer imaging. We have achieved a 1 nm spatial resolution, which is better than conventional TEM can provide for such a low contrast sample at the same exposure. A principal advantage of STEM imaging is the fact that STEM does not require any defocus to improve contrast in the image. It is also important that HAADF imaging may be more sensitive to heavier elements such as sulfur. In spite of the expectation to see a lot of damage in the STEM and EELS imaging we were able to collect the data under very high dose (106 e/nm2). Lower local temperature rise in STEM may contribute to this stability. As a result of our study we observed lamellar type of morphologies with different levels of order. We found that very thin sections with highly ordered lamella morphology are not stable at the room temperature and have to be cryo-microtomed and cryo-imaged. In contrast thin sections with disordered morphology are more stable and can be imaged at room temperature. Cast films typically show highly disordered morphology that becomes more pronounced but usually does not change with the annealing.
10:15 AM - FF6.4
Flexible Supercapacitor from Hydrogel/Conducting Polymer Hybrid Microfiber.
Yahya Ismail 1 , Seon Kim 2 , Jinho Chang 3 , Rajaram Mane 3 , Sung Han 3
1 Department of Biological Sciences and Chemistry, University of Nizwa, Nizwa - 616 Oman, 2 Creative Research Initiative Center for Bio-Artificial Muscle, Department of Biomedical Engineering , Hanyang University, Seoul - 133-791 Korea (the Republic of), 3 Department of Chemistry, Hanyang University, Seoul - 133-791 Korea (the Republic of)
Show AbstractObtaining giant capacitance in porous nanostructured electrode materials serving as actuators at low operating voltages is one of the great challenges in designing bio-artificial muscles. We report a high capacitance achieved in a flexible and stable hydrogel-assisted polyaniline electrochemical supercapacitor (HAES) microfiber whose specific capacitance can be varied by the application of external stress. The HAES microfiber was fabricated through a wet spinning of a chitosan solution, followed by the in-situ chemical polymerization of aniline. The microfiber could utilize the large surface area by allowing all volume elements at the nanoscopic level to be in contact with the electrolyte. The HAES microfiber was characterized by electrical conductivity measurements, cyclic voltammetry, chronopotentiometry, impedance measurements, and scanning and transmission electron microscopic techniques. The HAES microfiber exhibited a specific capacitance of 703 F/g with an initial electrochemical actuation strain of 0.33% in 1 M methane sulphonic acid, more than 3000 cycle charging/discharging durability and an electrical conductivity of 0.16 Scm-1. Insertion of polyaniline in the hydrogel matrix was confirmed by EDAX. FESEM images showed the growth of nanostructured polyaniline on the surface of the hydrogel microfiber. The cross sectional FETEM images revealed the deep insertion of nanostructured polyaniline inside the hydrogel matrix thus reducing the diffusion length of ion to cause efficient Faradaic redox reaction. A very high inner charge contribution of 99% was achieved due to the utilization of the whole polyaniline in HAES microfiber. The specific capacitance and impedance of the HAES microfiber was modulated by the controlled applied stress. The cylindrical form of HAES fiber provided the perfect utilization of ion diffusion throughout the curvature.
10:30 AM - FF6.5
DFT Study of the Initial Polymerization Steps During Initiated CVD of PGMA Thin Films.
Marites Violanda 1 , Ruud Bakker 1 , Henrik Rudolph 1
1 Nanophotonics Section, Debye Institute for NanoMaterials Science, Department of Physics and Astronomy, Utrecht University, Utrecht Netherlands
Show AbstractGlycidyl methacrylate (GMA) functional monomers have long been used as a main chemical component for surface coatings. Their potential in photovoltaic applications has also recently been explored. It is envisaged to integrate the polymer of GMA (polyglycidyl methacrylate or PGMA) into low-cost solar cell devices as a protective layer that helps prevent device degradation. Recently, PGMA thin films have been successfully grown on various substrates using initiated chemical vapor deposition (iCVD) with tert-butyl peroxide (TBPO) as the initiator. Precise control of the deposition of the nanometer-thick PGMA thin films requires detailed understanding of the polymerization process during the deposition step. To this end, we have performed atomistic calculations of the initial steps of PGMA polymerization using a density functional theory (DFT) based molecular dynamics technique. The polymerization process both in the gas phase and in the presence of a substrate is investigated. The bonding of the radical O-end of the dissociated TBPO initiator to either one of the C atoms in the vinyl group of the GMA monomer is considered the first important reaction step towards polymerization at low temperature. Stable bonding geometries and further reaction pathways of the GMA polymerizations are also determined. Vibrational properties of the grown polymers are calculated and compared with the experimental FTIR spectra.
10:45 AM - FF6.6
The Effect of Process and Polymer Chemistry on Proton Transport and Ordering in High Temperature Proton Exchange Membranes based on Phosphoric Acid-doped Polybenzimidazole.
Kelly Perry 1 , Karren More 2 , Roberta Meisner 3 , E. Andrew Payzant 2 , Bobby Sumpter 4 , Brian Benicewicz 5
1 Chemistry and Chemical Biology, Rensselaer Polytechnic Institute, Troy, New York, United States, 2 Materials Science & Technology Division, Oak Ridge National Laboratory, Oak Ridge, Tennessee, United States, 3 Materials Science and Engineering, University of Tennessee, Knoxville, Tennessee, United States, 4 Computer Science & Mathematics Division and Center for Nanophase Materials Sciences, Oak Ridge National Laboratory, Oak Ridge, Tennessee, United States, 5 Chemistry and Biochemistry & USC NanoCenter, University of South Carolina, Columbia, South Carolina, United States
Show AbstractImportant properties for high-temperature proton exchange membranes (PEMs) used for electrochemical energy conversion and gas purification devices include (1) rapid proton transport, which can be increased by the addition of acidic groups that aid in vehicular and/or Grotthuss diffusion and (2) the mechanical integrity of the polymer. Phosphoric acid (PA)-doped polybenzimidazole (PBI) membranes are currently commercialized for high temperature fuel cells and hydrogen pumps and the effects of process and polymer chemistry on the properties of these membranes have been investigated in this research. PA-doped m-PBI membranes (5PA/rpu with 33wt% solids) produced by conventional acid immersion in 85wt% PA have achieved ionic conductivities up to 0.09S/cm at 160°C. With the development of sol-gel processing[1] that permits in-situ PA-doping, the ionic conductivity of m-PBI membranes (6PA/rpu and 31wt% solids) increased to 0.15S/cm and when the rigidity of the polymer chain in the membrane (18PA/rpu and 12wt% solids) was increased, a higher ionic conductivity of 0.28S/cm was achieved. Lastly, the incorporation of hydroxyl groups on this more rigid PBI membrane (18PA/rpu and 14wt% solids) further increased the ionic conductivity to 0.31S/cm. Tensile testing of PA-doped PBI membranes showed that conventional PA-doped m-PBI had relatively high mechanical properties (modulus (M) = 0.4±0.01MPa, stress at yield (σ) = 6±0.4MPa, and at maximum (σ') = 17±5MPa), which were dramatically reduced following heat treatment at 120°C to M = 0.4±0.09MPa, σ = 4±0.6MPa, and σ' = 8±2MPa. Conversely, the sol-gel PA-doped PBI membranes having different rigidity and functionalization exhibited an increase in mechanical performance with heat treatment (M = 0.01-0.05 increased to 0.09-0.28MPa and σ = 0.3-0.5 increased to 1.0-2.9MPa), which corresponded with increased ordering observed in wide-angle X-ray scattering (WAXS) data. The WAXS spectra showed two predominant spacings (corresponding with polymer chain packing) for heat-treated PA-doped m-PBI membranes at 3.5 and 4.6Å, regardless of process used. Atomistic simulations indicate significant face-to-face packing of the heterocylic rings, in good agreement with similar structures.[2] The more rigid p-PBI membranes exhibited a similar spacing at 3.5Å, with additional spacings at 3.9, 4.3, and 5.1Å. This presentation will summarize electrochemical, mechanical, and structural analyses of PA-doped PBI membranes produced by two processes and with different polymer chemistry.(1) Xiao et al. Chem. Mat. 2005, 17, 5328. (2) Cho et al. JPS B. 2004, 42, 2576.Research at the Oak Ridge National Laboratory SHaRE User Facility and Center for Nanophase Materials Science was sponsored by the Scientific User Facilities Division, Office of Basic Energy Sciences, U.S. DOE. A portion of this work also was supported by DOE’s Office of Fuel Cell Technologies, the NSF IGERT Fellowship Program, and the HERE Program at ORNL.
11:30 AM - **FF6.7
The Hydration and Transport of Protons in Model Polymeric Systems Possessing High Perfluorosulfonic Acid Density and Minimal Water.
Stephen Paddison 1
1 Chemical and Biomolecular Engineering, University of Tennessee, Knoxville, Tennessee, United States
Show AbstractProton exchange membranes (PEMs) exhibit a nanophase-separated morphology when utilized as the electrolyte in current fuel cells. Although a large number of strategies have been devised in the pursuit to design materials that meet the requirements of high proton conductivity (> 10-2 Scm-1) under low humidity conditions, long-time thermal and chemical stability (including resistance to oxidation and degradation by reactive species) at temperatures above 100 °C, current PEM fuel cells still utilize perfluorosulfonic acid (PFSA) ionomers such as Nafion®. Both experiments and modeling have shown that the transport of water and hydrated protons within PFSAs is dependent upon: the characteristic dimensions of the phase-separated morphology of the hydrated polymer (typically on the order of only a few nanometers); acidity, density, and distribution of the sulfonic acid groups; and the external conditions including humidity, temperature, and pressure. A complete understanding of how all these factors may be used in a synergetic fashion in the engineering of high performance materials remains elusive.Recently we have undertaken ab initio molecular dynamics simulations of perfluorosulfonic systems with either known structures or a priori designed structures in an effort to elucidate the factors determining the solvation and transport of protons in PFSA membranes under conditions of little water and high sulfonic acid density. These systems include the mono-, di-, and tetra- hydrates of triflic acid and carbon nanotubes of various diameters decorated with distinct densities of perfluorosulfonic acid groups. Our simulations clarify the role of the mobility, connectivity, and separation of the sulfonic acid groups along with the presence of fluorine on the dissociation and transfer of protons in these systems with little water. Implications of the results from these ideal systems on low equivalent weight PFSA membranes will be discussed.
12:00 PM - FF6.8
PM-IRRAS: Nafion-Surface Interaction.
Adam Yakaboski 1 , Matthew Webber 1 , Eugene Smotkin 1
1 Chemistry and Chemical Biology, Northeastern University, Boston, Massachusetts, United States
Show AbstractIn fuel cell membrane electrode assemblies, metal catalysts are in direct contact with the proton exchange membrane. Wetting of the catalyst by the hydrated polymer electrolyte is required for transport of protons to and from the catalytic layers. A complete understanding of interactions between the ionomer and metal surface is required if better electrode structures are to be developed. Polarization Modulation Infrared Reflection Absorption Spectroscopy (PM-IRRAS) was used to probe the interface between Nafion and a platinum surface. PM-IRRAS identifies which peaks are due to surface-active functional groups and the effect of potential on the surface activity.
12:15 PM - FF6.9
Glycerol Based Nafion Dispersions for Improved Fuel Cell Durability.
Rex Hjelm 1 , Yu Seung Kim 2 , Christina Johnston 2 , Tommy Rockward 2 , Andrea Labouriau 3 , Cynthia Welch 3 , Edward Orler 3 , Marilyn Hawley 4 , Kwan-Soo Lee 2
1 Los Alamos Neutron Science Center, Los Alamos National Laboratory, Los Alamos, New Mexico, United States, 2 Sensors and Electrochemical Devices Group, Los Alamos National Laboratory, Los Alamos, New Mexico, United States, 3 Polymer and Coatings Group, Los Alamos National Laboratory, Los Alamos, New Mexico, United States, 4 Structure/Property Relations Group, Los Alamos National Laboratory, Los Alamos, New Mexico, United States
Show AbstractModern polymer electrolyte fuel cells (PEFCs) require technologies that generate higher performance and durability. The primary factor in determining durability was thought to be the extent of coarsening of the Pt electro-catalyst nano-particles in the potential cycling test.1 Such coarsening results in a loss of electrochemical surface area (ECSA), resulting in a loss of performance. However, we contend that an equally important, or possibly a more important, factor in determining durability lies in the microstructure of the electrode thin film layer. This electrode layer consists of the catalyst particles dispersed in a polymeric binder (usually a perfluorosulfonic acid), and is prepared from a solvent dispersion. In this communication, we present evidence that the polymer/solvent interactions within the dispersion dictate the final morphology and thereby affect the durability of the electrode. We do so by comparing data from 19F NMR, small angle neutron scattering (SANS) for polymer dispersions and atomic force microscopy (AFM) for solid state films created with two different solvent systems: the standard aqueous mixture (1:1:1 by volume of water:1-propanol:2-propanol) and a non-aqueous, single solvent (propane-1,2,3-triol, or glycerol).
12:30 PM - FF6.10
Electrochemical Characteristics of Ni-yttria Stabilized Zirconia Coated 316L Stainless Steel Under Simulated PEMFC Environment.
Wan Gyu Lee 1 , Ho Jang 1
1 Materials Science and Engineering, Korea University, Seoul Korea (the Republic of)
Show AbstractThe PEMFC (proton exchange membrane fuel cell) is a clean energy system that can convert hydrogen and oxygen (or air) to electricity with water as the only chemical by product. The bipolar plates are a multifunctional component in fuel cell stack playing a significant role in providing electrical continuity between the cells, separating gases, and gas flow channels. In general, the materials applicable to bipolar plates are required to possess high corrosion resistance and low contact resistance together with good thermal and electrical conductivity, and easy fabrication. Surface treated austenitic stainless steels have been attracted great attention due to their favorable properties for those requirements. Therefore, a study was initiated from the examination of corrosion resistance of Ni-yttria stabilized zirconia (Ni-YSZ) coated 316L austenitic stainless steel because zirconia sol-gel method is known to produce favorable properties such as good adherence on metallic substrates, the good corrosion resistance, high mechanical strength, chemical durability, and similar thermal expansion coefficient to stainless steels. The Ni-YSZ coating on a 316L stainless steel was performed using a sol-gel dip coating method and electrochemical tests were carried out at 80°C in 1M H2SO4 solution to accelerate corrosion. The results showed that the formation of cracks on the film was changed with different Ni contents added in the YSZ precursor. Potentiodynamic tests showed that the corrosion resistance of the 10wt.% Ni-YSZ coated 316L stainless steel was improved than that of bare stainless steel by one order of magnitude compared to the bare specimen in terms of the current density. The optimum interfacial contact resistance (ICR) of the film under a compaction load of 150N was found with changing Ni contents. However, in the case stainless steel coated Ni over 10wt.%, the their ICR was increased.