Recent work has shown that large increases in the kinetic current for the oxygen reduction reaction (ORR) on nanoporous catalytic electrodes are seen when the pores of the electrode are filled with an ionic liquid (IL) with a greater oxygen solubility than aqueous solutions in which the electrode is immersed, as the IL creates a bias to drive diffusion of oxygen to the catalyst surface [J. Snyder, et al., Adv. Func. Mat., (2013), 5494; Chen, et al, Science, (2014), 1339]. The particular details of the kinetic current increase, however, depend on other physical properties of the IL used, including its physical thickness, viscosity, etc. Here, we discuss quantitative measures of the relative impact of IL physical properties and chemical structure on the kinetic current during oxygen reduction using nanoporous Ni/Pt (np-NiPt) electrodes fabricated using electrochemical dealloying. These high surface catalytic electrodes have pore and ligament sizes each approximately 3-5 nm in diameter that we fill with an ionic liquids (IL) of controlled thickness that serves as an intermediate layer between the catalyst and an electrolyte. In this presentation, we will discuss how the properties of the IL layer affect oxygen reduction in acid electrolyte in a flow cell apparatus. Particular attention will be focused upon IL proton conductivity (protic vs. aprotic), oxygen solubility (higher or lower than the aqueous electrolyte), as well as viscosity. General understanding of this composite catalyst system will allow its adaptation to other electrocatalytic reactions, such as CO₂ reduction.

We have developed nano-particles formation system for catalysts by a dry
process. By use of a coaxial pulsed vacuum arc discharge system (CPVD),
highly ionized metal plasma can be generated from a target rod without any
discharge gases, and deposits on flat substrates or powders to form various
catalysts. Here, we investigate the electrocatalytic activity for oxygen
reaction reduction (ORR) of our PtC-5% catalyst which is prepared using
CPVD, For compression, commercially available PtC-20% (PtC-20%),
commercially available PtC-5% (PtC-5%), and Pt black are also tested. The
half-wave potential of our catalyst is higher than those of the others. The
currents of four catalysts at 0.80 V, normalized by Pt mass (mass activity)
and Pt electrochemically active surface area (ECSA) (specific activity),
are also investigated. In both cases, the activity is much higher than
those of the others, indicating that nanosized Pt particles prepared by our
method can highly improve the utilization efficiency of Pt in
electro-reduction of oxygen. The polarization curves are also recorded at
different rotation rates. The expected increase of the limiting diffusion
current density is observed as a function of the rotation rate. The
corresponding Koutecky-Levich (K-L) plots show the first-order reaction
kinetics toward the dissolved O2 on our catalyst from 0.3 V to 0.6 V. The
calculated number of transferred electrons during the reduction of oxygen
was between 4.03~4.18, thereby indicating that the ORR from 0.3 V to 0.6 V
is dominated by a four-electron (4e-) process and O2 is reduced to OH-.

Atomic structures of metal crystalline surfaces play key roles in determining reaction kinetics and mechanisms of catalytic reactions. Intrinsic correlations between surface structures and catalytic behaviors have been extensively investigated for the bulk single-crystalline surfaces. For example, on bulk gold (Au) surface, the oxygen reduction reaction (ORR) in alkaline electrolytes proceeds via a two-electron (2e) partial reduction to hydroperoxide ions (HO₂^-) on the majority of facets including Au {111}^[1], whereas the complete four-electron (4e) reduction to hydroxide ions (OH^-) occurs on Au {100}, albeit in a narrow potential region^[2]. The 4e ORR is preferred since energy conversion is twice as efficient compared with the 2e ORR. However, the reasons for such ORR behaviors on Au surfaces remain elusive.
In this work we generate Au {100} and {111} nanofacets from monodisperse nanocrystals with well-defined cubic and octahedral shapes, respectively, synthesized by a developed solution-phase method. These single-crystalline nanocrystals have narrow size distribution and clear surface termination, verified by several structural characterization techniques. The surface cleanness and high crystallinity of Au nanocrystals are confirmed by electrochemical characterizations including cyclic voltammetry (CV) and thallium underpotential deposition (Tl UPD). In addition, Au cubic and octahedral nanocrystals exhibit astonishing resemblance of the ORR behaviors to those on Au {100} and Au {111} single-crystalline surfaces, respectively. Furthermore, density functional theory (DFT) calculations are carried out to identify the structural factors determining ORR behaviors. The calculation results of molecular O₂ adsorption rationalize well the 2e-only activity on Au {111}. For the puzzling 4e-ORR on Au {100} in a narrow potential range, we propose that co-adsorbed water has an important role in the ORR process. The confined 4e-ORR on Au {100} is attributed to water co-adsorption at neighboring Au atoms with adsorbed diatomic oxygen, which facilitates proton transfer in concert with the oxygen-oxygen bond breaking. In summary, the ease of attaining single crystalline surfaces via highly pure Au nanofacets provides new opportunities for gaining comprehensive insights into electrochemical reaction mechanisms, and therefore, opens up new strategies for the rational design of catalyst materials by assuring the optimal catalyst surface.
[1] N. M. Markovicacute;, R. R. Adzicacute;, V. B. Vescaron;ovicacute;, J. Electroanal. Chem. 1984, 165, 121-133.
[2] R. R. Adzicacute;, N. M. Markovicacute;, V. B. Vescaron;ovicacute;, J. Electroanal. Chem. 1984, 165, 105-120.

Alkaline electrolyte membrane (AEM) fuel cells have received much attention since non-noble metal electrocatalysts are stable in high pH condition. Many literature reports have shown that Pd-based alloys are candidates for catalytic alcohol and formic acid oxidation reactions. All of the researchers plan to modify the electrocatalytic properties of Pd by alloying with other transition metals to create binary, ternary or quaternary alloys for more efficient ethanol electro-oxodation catalyst. Ethanol is an eco-friendly fuel, possesses a high theoretical energy density of 8030 Wh/kg, and is easily contained for transportation and delivery. Moreover, ethanol is also the second most extensively studied alcohol other than methanol for both acidic and alkaline electrolytes. However, the ethanol molecule contains a carbon-carbon (C-C) bond that makes the complete oxidation a challenge. The payoff for being able to break the C-C bond for direct ethanol fuel cell (DEFC) would have a profound impact on the fuel cell area. This presentation focuses on synthesis, characterization and the electrochemical performance of a ternary Pd-Ni-P electrocatalyst for the ethanol oxidation reaction (EOR) in alkaline media.

Ethanol is one of the most hopeful fuels renewable energy applications due to its low toxicity, high availability from biomass production, and high energy density due to the twelve-electron charge transfer upon complete oxidation. Complete oxidation of ethanol into CO₂ via C-C bond cleavage is mechanistically difficult. Platinum-tin (Pt/Sn) binary nanoparticles are active electrocatalysts for the ethanol oxidation reaction (EOR), but inactive for splitting the C-C bond of ethanol to CO₂. Most of the charge generated is from partial oxidation of ethanol to acetaldehyde and/or acetic acid, which only involve two- or four-electron transfer.
We reported the studies of CO₂ generation during the EOR on carbon supported non-alloyed Pt-SnO₂ and intermetallic PtSn nanocatalysts using a new type of in-situ CO₂ microelectrode. Electrochemical measurements showed that PtSn catalysts with intermetallic crystalline structure showed higher current densities for the EOR compared to commercial Pt/C and non-alloyed Pt-SnO₂/C. In contrast, chemical composition played a more important role in the CO2 generation: non-alloyed Pt/Sn showed better CO2 generation than pure Pt and Pt-Sn intermetallic catalysts. Our work demonstrates the CO₂ microelectrode can be used as an in-situ, time resolved technique to study the CO₂ generation during electrochemical reactions. Moreover, our results also provide microscopic insight on the important role of SnO₂ cluster of Pt/Sn catalysts on the CO₂ generation during the EOR.

Proton exchange membrane fuel cells have drawn great attention and been taken as a promising alternated energy source because of the high power output density, low operation temperature and “green” emission. The function of the fuel cell constitutes a balance between hydrogen oxidation and oxygen reduction reactions. Although the hydrogen oxidation process is a fast electrochemical reaction, challenges come up when impure hydrogen is used. Marvrikakis etal have predicted that gold nanoparticles that are platelet shaped and have direct contact to the substrate to be the perfect catalysts.
In our experiment, hydrophobic, thiol-functionalized gold nanoparticles were synthesized through two-phase method developed by Brust et al. We previously developed a technique to reproducibly form an Au nanoparticles layer with three atomic layers thick at the air water interface. After these nanoparticles are spread on the surface of water in a Langmuir-Blodgett trough where surface pressure can be applied to compress them, they form LB film consisting of one or more monolayers. Then we deposit these Au particles directly onto the Nafion membrane in the PEM fuel cell, resulting in 80% enhancement of the efficiency of the fuel cell. Furthermore, we find this kind of enhancement occurs only when the particles are in direct surface contact with the membrane and does not occur when the Nanoparticles are incorporated into the electrodes.

Li-air batteries have a much higher theoretical gravimetric energy storage density than all other candidate battery chemistries and this has led to a strong interest in developing such batteries for powering EVs, enabling driving ranges comparable to gasoline powered automobiles. However, many fundamental challenges need to be solved before these batteries can become practical. I will address three issues, based on density functional theory calculations and electrochemical modeling coupled with experiments, relating to the practicality of non-aqueous Li-air batteries - (1) Thermodynamic efficiency, (2) Deep discharge and (3) Rechargability of non-aqueous Li-air batteries.

On average each person on earth uses 0.5 kg H₂O₂ / year, mainly related to paper and chemicals production. While already a high amount, if H₂O₂ could be synthesized on-site from oxygen and water it could be used for new applications, in particular water purification. The electrochemical production of H₂O₂ provides an attractive means of fulfilling these requirements¹. Oxygen could be reduced at the cathode of a fuel cell or electrolyzer, yielding H₂O₂ as a product. Contingent to the realization of this technology is the development of a cathode catalyst that is active, selective and stable. On the basis of microscopic insight, we recently discovered a new class of catalysts for H₂O₂ production; these were based on isolated active sites of an oxophilic element surrounded by inert atoms. Experimental tests in acidic solution confirmed that these catalysts exhibited superior catalytic properties, far exceeding the current state-of-the-art^2,3. We now extend the search to alkaline electrolytes, finding significant differences in activity and stability for these single site catalysts. This opens up new possibilities for oxygen reduction electrocatalysis we explore in the current work.
Campos-Martin, J. M., Blanco-Brieva, G. and Fierro, J. L. G. Hydrogen peroxide synthesis: an Outlook beyond the anthraquinone process. Angewandte Chemie Int. Ed. 45, 6962-6984.
Siahrostami, S., Verdaguer-Casadevall, A., Karamad, M., Deiana, D., Malacrida, P., Wickman, B., Escudero-Escribano, M., Paoli, E. A., Frydendal, R., Hansen, T. W., Chorkendorff, I., Stephens, I. E. L. and Rossmeisl, J. Nature Materials 12, 1137-1143.
Verdaguer-Casadevall, A., Deiana, D., Karamad, M, Siahrostami, S., Malacrida, P., Hansen, T. W., Rossmeisl, J., Chorkendorff, I. and Stephens, I. E. L. Nano Letters 14, 1603-1608.

The proton exchange membrane fuel cell (PEMFC) has been a key candidate in scientific research in effort to replace the internal combustion engine. Conventionally, PEMFC electrodes are composed of a carbon black support with Pt catalysts, as Pt is the most efficient homocatalyst for the oxygen reduction reaction (ORR). Further enhancement of the electrode is possible through the use of a graphene support, as it offers an increased electrical conductivity and a larger surface for catalyst deposition.^1,2 However, the sp² bonding of the C lattice produces a chemically inert surface which prevents the Pt from readily adsorbing on the graphene, leading to a poor Pt distribution and the formation of nanoparticles. The introduction of defects in the graphene lattice can facilitate Pt adsorption, where functionalization with N-dopants have the additional benefits of acting as ORR sites and increasing the Pt-C binding energy.^3,4 Further, by tuning the Pt deposition process using the atomic layer deposition (ALD) technique, ultra-small Pt nanoparticles (<1 nm) or clusters can be achieved, thus enhancing the Pt utilization and reducing the overall cost of the PEMFC.
Full understanding of efficiency measurements must be coupled with atomic level characterization to determine the effect of the size and size distribution of Pt, the predominant N-dopant species (amino, pyridinic, pyrrolic, and graphitic) within the lattice, and the graphene structure. Sub-aring;ngstrom resolution imaging becomes possible with the use of aberration-corrected transmission electron microscopes (TEM). As an initial investigation, thermally reduced/exfoliated graphene was N-doped in an ammonia environment.⁵ High resolution TEM (HRTEM) showed that the atomic structure of the graphene lattice was maintained on the short range order, however long range order was lost due to the presence of folds, defects, and incomplete exfoliation.⁵ Through the use of high angle annular dark field (HAADF) imaging, we revealed that the Pt forms atoms and clusters on the N-doped graphene, where an increase in ALD cycles did not result in the formation of nanoparticles.⁵ Further it was determined that the Pt sits predominantly at edge locations with few atoms sitting on the N-doped graphene surface. Lastly, using electron energy loss spectroscopy we found that each possible N-dopant was present in the graphene lattice; however the specific distributions across sheets were inhomogeneous.⁵ This material suggests the possibility of creating a platform for producing stabilized Pt atoms/clusters for the PEMFC electrode, which would greatly increase the surface area to volume ratio of the catalyst.
1. Geim, A. K. Novoselov, K. S, Nat. Mater. 6 (2007), p.183-191.
2. Lee, C. et al.Science 321 (2008), p.385-388.
3. Wei, D. et al. Nano Lett. 9(2009), p.1752-1758.
4. Holme, T. et al. Phys Chem Chem Phys, 12, (2010), 9461-9468.
5. Stambula, S. et al. J. Phys. Chem. C, 118, (2014), p. 3890-3900.

There has been tremendous research effort in the field of renewable energy sources in recent years. One interesting and promising aspect focuses on using biomass-derived fuels in combination with highly efficient fuel cells, for example, in reformed alcohol fuel cell systems. A major issue with these systems is the production of small amounts of CO during the conversion of alcohol and water to hydrogen-rich reformate gas by steam reforming. Even small amounts of CO are capable of quickly poisoning and deactivating the catalyst of low-temperature proton exchange membrane fuel cells (PEMFCs). One possible solution is the preferential oxidation (PROX) of CO before feeding the hydrogen-rich gas to fuel cells. Unfortunately, no existing catalyst has been able to convert CO effectively to safe levels below 20 ppm in the presence of significant amounts of unreacted H₂O and by-product CO₂.
We performed particle size analysis of the catalyst to determine the morphology of the catalyst at specific stages during synthesis. This allows us to tune the PROX catalyst for our specific needs. As a result, we have developed a novel Au/α-Fe₂O₃ catalyst with the capability of 99.85% CO conversion, which is the highest conversion documented under these realistic fuel reforming conditions. The direct and successful combination of steam reforming and PEMFCs has never been proven before, due to the missing link of efficient CO removal between H₂ generation and fuel cells. In this study, we investigated the ability of the catalyst to effectively oxidize CO in a H₂-, H₂O-, and CO₂-rich environment by integrating the novel PROX catalyst into a low-temperature PEMFC. We demonstrate how the toxic and non-toxic products of methanol-steam reformation affect the performance and robustness of the PEMFC over time. Finally, we show the first fully integrated steam reformer-PROX-fuel cell system and demonstrate that the Au/α-Fe₂O₃ material has sufficient catalytic activity to operate the PEMFC under high performance without long-term deactivation.

The Molten Carbonate Fuel Cell (MCFC) is one of the most mature and efficient fuel cell technologies. The performance of MCFCs critically depends on advanced porous ceramic materials, which must be long-term stable under different atmospheres in molten carbonate environment at temperatures as high as 650 °C. Improvement of stability requires a deeper understanding of coarsening of porous ceramic materials. So far, for LiAlO₂ the α→γ phase transformation and its coarsening mechanisms are insufficiently understood.
Here, highly porous, pure phase α-LiAlO₂ and mixed phase α,γ-LiAlO₂ nanopowders with specific surface areas in the range of 50-100 m²/g were synthesized using a solid state reaction method. The calcination time and temperature were varied in the range of 5-20 h and 500-600 °C, respectively. The prepared nanopowders were then heat treated at constant temperature of 800 °C in air for 12-96 h. The crystalline structure, vibration modes, porosity, thermodynamic properties and morphology of the powders were characterized by XRD, FTIR, Brunauer-Emmett-Teller (BET) method, differential thermal analysis, scanning electron microscopy as well as XTEM. It is shown that the coarsening exponents as determined by XRD and BET differ, i.e. the mean size of nanocrystals evolves other than porosity. In order to interpret the experimental results, the kinetic Monte-Carlo simulations are being performed in assumption of the diffusion and reaction controlled coarsening.

So far most electrocatalyst has been designed only based on reactivity of the surface. This single parameter is not sufficient to optimize the activity and selectivity. This means that activities and selectivity can only be optimized to a certain point. The activity as function of the surface reactivity is often represented in volcano curves. Electrocatalytic activity and selectivity is ultimately determined by the atomic and electronic structure of the catalyst surface. By controlling the atomic structure of the catalyst surface it is possible provide more parameters besides the reactivity to tune activity and selectivity beyond the normally limits. I will show some examples on atomic scale design of special electrocatalytic sites for oxygen evolution and oxygen reduction for better selectivity and activity.

Alloying Pt with 3d transition metals (typically Fe, Co and Ni) is known to improve the catalytic activity with respect to pure Pt/C. However, structurally disordered nanoparticles are found to be less durable during the lifetime of PEMFCs. As a progression from such disordered systems, we discuss an emerging new class of ordered electrocatalysts composed of an intermetallic alloy core encapsulated within a Pt-rich shell [1]. These catalysts were found to exhibit an increased mass activity (228%) and an enhanced catalytic activity (155%) for the oxygen reduction reaction (ORR) compared to Pt/C [2]. We have quantified the time-evolution of their structural ordering (over the course of cycling) with an aberration corrected scanning transmission electron microscope (STEM). Our findings suggest that these particles exhibit a static core - dynamic shell (SCDS) regime wherein despite treating over 10,000 cycles, there is negligible decrease (9%) in catalytic activity. Further, the ordered alloy core remained virtually intact while Pt-shell suffered a continuous enrichment. In addition, with an atomic-scale two-dimensional (2-D) surface relaxation mapping, we show that the Pt atoms on the surface are slightly relaxed with respect to bulk. The cycled nanocatalysts were found to exhibit a greater surface relaxation compared to non-cycled catalysts. With 2-D lattice strain mapping we show that the particle was about -3% strained with respect to pure Pt. While the observed enhancement in their activity is ascribed to such a strained lattice, our findings on the degradation kinetics establish that their extended catalytic durability is attributable to a sustained atomic order.
In the light of these observations, the atomic-ordering and a compositional segregation of Pt (towards the shell) are found to be dictating the overall performance of a nanocatalyst design. Through single-nanoparticle phase transformation using atomic-resolution STEM imaging and electron energy loss spectroscopy in-situ, we illustrate an ongoing interplay between segregation and ordering and discuss strategies to control the evolution of these ordered structures during heat treatment. Finally, we present our results on potential cycling of Pt-alloy nanoparticles in-situ in a TEM and provide direct evidence to their growth kinetics mediated by ripening and structural durability under a native electrolyte environment.
References:
[1] Prabhudev, S.; Bugnet, M.; Bock, C.; Botton, G. ACS Nano 7 6103-6110 (2013)
[2] Chen, L.; Chan, M. C. Y.; Nan, F.; Bock, C.; Botton, G. A.; Mercier, P. H. J.; MacDougall, B. R. ChemCatChem 5 1449-1460 (2013)

The development of design and control of more sophisticated nanostructures can lead to the discovery of new materials, often with exceptional properties. Recently, generating lattice strain in metallic nanoparticles has attracted much attention as a way to improve the performance of energy conversion electrocatalysts for fuel cell technologies. We focus on the design of strained nanoparticle architectures that could be used as surface electronic structure-engineered catalytic materials for fuel cell electrodes, which suffer from slow oxidation and reduction reaction kinetics. The current state-of-the-art fuel cell catalysts are shaped M-Pt alloy nanoparticles and have advanced our understanding of different ligand, ensemble, geometric, and restructuring effects. We show a new design principle of core-sandwich-shell nanoparticles that can elucidate the mechanisms behind lattice strain as well as overcome some of the synthetic challenges of bimetallic alloy nanoparticles, such as restricted tunability and surface segregation. The novel synthesis of shaped Pd-Ni-Pt core-sandwich-shell nanoparticles offers a multi-faceted optimization of lattice strain (surface d-band) by the tunable size/shape of Pd substrate and thickness of the Ni sandwich and Pt shell. The sandwich catalysts are used to isolate the strain effect in methanol and formic acid electrocatalytic oxidations, and show higher current densities for increased Ni layer thickness (increased Pt surface strain). We then show the design concept can be extended to smaller, more industrially relevant particle sizes, with a doubling of specific activity. Quaternary metal (core-triple-shelled) and octahedral nanoparticles can also be fabricated at this size scale with the method, the latter of which hold promise as highly active oxygen reduction catalysts. We believe this new design principle will ultimately lead to more sophisticated nanomaterials with atomic-level control of the surface electronic structure and catalytic active sites for fuel cell technologies and other energy-related heterogeneous catalysis.
References:
1. B.T. Sneed et al. “Shaped Pd-Ni-Pt Core-Sandwich-Shell Nanoparticles: Influence of Ni Layers on Electrooxidation.” ACS Nano, 2014. DOI: 10.1021/nn502259g (just accepted manuscript).
2. C.H. Kuo et al. “The Effect of Lattice Strain on the Catalytic Properties of Pd Nanocrystals.” Chem. Sus. Chem. 6, p. 1993, 2013.
3. B.T. Sneed et al. “Nanoscale-Phase-Separated Pd-Rh Boxes Synthesized via Metal Migration: An Archetype for Studying Lattice Strain and Composition Effects in Electrocatalysis.” J. Am. Chem. Soc. 135 (39), p. 14691, 2013.
4. B.T. Sneed et al. “Iodide-Mediated Control of Rhodium Epitaxial Growth on Well-Defined Noble Metal Nanocrystals: Synthesis, Characterization, and Structure-Dependent Catalytic Properties.” J. Am. Chem. Soc. 134 (44), p. 18417, 2012.

In this presentation, a research system that connects fundamental investigation on well-defined extended surfaces (e.g. single crystal surfaces), theoretical studies using computer-powered simulation, and finally design of high performance catalysts in which all the possible beneficial properties from complex functional structures are implemented, will be demonstrated. Control of structure at the atomic level can precisely and effectively tune catalytic properties of materials, enabling enhancement in both activity and durability. To mimic the optimal surface structure of Pt₃Ni(111)-Pt-Skin for oxygen reduction reaction (ORR), a highly active and durable class of electrocatalysts are prepared by exploiting the structural evolution of Pt-Ni bimetallic nanocrystals. The starting material, crystalline PtNi₃ polyhedra, transformed in solution by interior erosion into Pt₃Ni nanoframes with surfaces that have three-dimensional molecular accessibility. The edges of these PtNi₃ polyhedra, which were Pt rich, are maintained in the final Pt₃Ni nanoframes. Both the interior and exterior catalytic surfaces of this open framework structure are composed of the nano-segregated Pt-Skin structure that exhibits enhanced oxygen reduction reaction (ORR) activity. The Pt₃Ni nanoframe catalysts achieved over 36 and 22-fold enhancement in mass and specific activities, respectively, for this reaction versus ORR in comparison to state-of-the-art Pt/C catalysts during prolonged exposure to reaction conditions. Notes and references: 1.Stamenkovic et al.Science 315, 493-497 (2007). 2.Kang et al.Science 343, 1339-1343 (2014)

Cathodic corrosion is an outstanding method for producing highly-active and clean nanoparticles, not only of Pt, but also of many metals¹, metal alloys² and oxides³. This method is substantially more efficient than other methods for high-yield synthesis of catalysts and can therefore be applied to solving the fuel cell efficiency and cost issues. The cathodic corrosion method allows the unique control of the size distribution, shape and chemical composition of the nanoparticles.^1,4,5 Because the cathodic corrosion method does not use any organic components during the synthesis, the resulting metal, metal-alloy or oxide nanoparticles are directly usable for catalytic application.
We will report the superior properties of alloy nanoparticles and supported nanoparticles prepared by the cathodic corrosion method towards the CO, formic acid and alcohol oxidation. The preparation and catalytic activity of PtBi, PtSn, PtPb, PtPd and ternary alloys will be presented. In addition, we will demonstrate the versatility of the cathodic corrosion method to prepare in one single step metal nanoparticles supported on conductive oxides ³.
In order to gain information of the reaction rates of CO₂ production we will show the On-line Electrochemical Mass Spectroscopy (OLEMS) results.
(1) Yanson, A. I.; Rodriguez, P.; Garcia-Araez, N.; Mom, R. V.; Tichelaar, F. D.; Koper, M. T. M. Angewandte Chemie International Edition2011, 50, 6346.
(2) Rodriguez, P.; Tichelaar, F. D.; Koper, M. T. M.; Yanson, A. I. J. Am. Chem. Soc.2011, 133, 17626.
(3) Rodriguez, P.; Plana, D.; Fermin, D. J.; Koper, M. T. M. Journal of Catalysis2014, 311, 182.
(4) Yanson, A. I.; Antonov, P. V.; Rodriguez, P.; Koper, M. T. M. Electrochimica Acta2013,112,913
(5) Duca, M. R., Paramaconi; Yanson, Alex; Koper, M.T.M Topics in catalysis2014, 57, 255.

While the commercialization of fuel cells has been started in various applications such as residential and distributed power, longer life time is still essential for future-generation fuel cell systems. In this invited presentation, an overview is given on degradation mechanisms of solid oxide fuel cells and polymer electrolyte fuel cells, especially related to their electrodes, where such degradation can occur due to intrinsic or extrinsic effects in steady-state operation and/or in dynamic operation such as cycling. After classifying such mechanisms experimentally revealed and/or thermochemically expected, results of some case studies for alternative/model materials are presented. Importance of advanced characterization techniques, international collaboration, and industry-academia collaboration is discussed to demonstrate and realize a fuel-cell powered society.

We explore combinatorially sputter deposited nitride thin films containing Ti, Ta, Nb, Cr, and Al as replacements for carbon catalyst supports used in proton exchange membrane (PEM) fuel cells. Conductive probe atomic force microscopy (cp-AFM) was used as a high throughput tool to screen electrical conductivity as a function of composition. This work is motivated by observations that carbon particles traditionally used as catalyst supports in fuel cells are oxidized to CO₂ at high potentials (~1.5 V), which exist at the cathode during startup and shutdown and under fuel starvation conditions. More durable supports are thus desired. Pourbaix diagrams reveal oxides of Ti, Ta, Nb, and W (TiO₂, Ta₂O₅, Nb₂O₅, WO₃) are thermodynamically stable at the high potentials and low pH experienced in PEM fuel cells, yet these oxides do not meet the requirement that catalyst supports must be as electrically conductive as the fuel cell electrolyte is ionically conductive. Knowing that nitrides, such as those of Ti or Cr, exhibit high electrical conductivity and that the oxidation of nitrides is thermodynamically favored, we hypothesize that surface oxidation of nitrides could wed the durability and electrical conductivity necessary for high performing catalyst supports. We found that materials with the desired conductivity can be synthesized through appropriate control of the amount of Ti, Ta, Nb, Cr, and Al in these nitride films.

Transition metal carbides, nitrides, sulfides and phosphides have been extensively explored as superior catalysts and/or catalyst supports in various fuel cell technologies including hydrogen evolution reaction (HER) and oxygen reduction reaction (ORR) for polymer electrolyte membrane (PEM) fuel cells. The addition of a second transition metal is expected to fine-tune electronic properties of the resulting bimetallic compounds and thus improvement as catalyst and support material. Recently, we reported synthesis of multiple phases of bimetallic carbides of Fe, Co and Ni with Mo and W at significantly reduced temperatures (between 950°C and 1040°C) using carbothermic reduction of stable oxides. The synthesis of size controlled bimetallic carbides at low temperature will make the catalysts more active as well as cost effective and environment friendly. We demonstrated control over dispersion of carbide particles in carbon network via modifications in the synthesis methods. This will improve stability of the bimetallic carbides as support materials. Monometallic carbides, nitrides, phosphide and sulfides of Mo, W and other transition metals have shown very promising HER and ORR activities in previous investigations. Testing of our bimetallic carbides for HER and ORR has revealed significant activity and stability. This presentation will discuss the synthesis method that enabled us to produce a range of bimetallic carbides and also compare their HER and ORR activities and stability with other catalysts.

Engineering nanocrystals with size, shape, composition and structure control for enhancing oxygen reduction reaction (ORR) and small molecule oxidation reactions is highly desirable for promoting the development of fuel cell devices. In this presentation, I will focus on my recent advances in rational design and controlled synthesis of high-quality multicomponent nanocrystals for enhancing ORR and small molecules oxidation reactions. I will start with three examples on how to engineer FePt NWs, FePtPd/FePt core/shell nanowires (NWs) and graphene-FePt nanoparticles (NPs) composite for getting advanced Pt-based catalysts for ORR with extremely high activity and stability. After that, I will move to non-Pt catalysts such as graphene-Co/CoO NPs and M/CuPd NPs (M=Ag, Au), which exhibit comparable and even higher ORR activity and stability than commercial Pt catalyst. Finally, I will show two interesting examples on how to engineering trimetallic NPs and NWs for enhancing methanol and formic acid oxidation reactions.

The development of low-cost catalysts for hydrogen evolution is of significant importance to realize the envisaged hydrogen economy. Additionally, alternative methods for hydrogen production, especially hybrid technologies capable of storing energy as both electricity and hydrogen, should be investigated to obtain optimum system performance and enhance the flexibility of energy storage systems. In terms of energy storage, redox flow batteries (RFBs) are very well suited for storing the intermittent excess supply of renewable electricity.¹ However, conventional RFBs cannot in many situations utilize all the available “junk” electricity due to a limited storage capacity.
Recently we proposed an alternative method to discharge the battery chemically to produce hydrogen rapidly and efficiently.^2,3 The proposed dual-circuit RFB can operate conventionally, storing and delivering electrical energy, or at periods of excess electricity, the charged negative electrolyte can be diverted through a secondary circuit and catalytic bed where the electrolyte is discharged by converting protons to hydrogen. This approach is designed to complement electrochemical energy storage and may circumvent the low energy density of RFBs especially as hydrogen can be produced continuously whilst the RFB is charging.
The dual-circuit RFB requires an efficient and low-cost catalyst for hydrogen evolution. We have recently demonstrated that molybdenum carbide (Mo₂C)⁴ can be utilized to catalyze hydrogen evolution by an electrolyte containing vanadium(II), resulting in 100 % yield of hydrogen.² Here we will present the latest results on the Mo₂C catalyzed hydrogen evolution reaction, including an ongoing project to scale-up the hydrogen production process to the demonstrator level using a 10 kW dual-circuit all-vanadium redox flow battery.
¹B. Dunn, H. Kamath and J. M. Tarascon, Science, 2011, 334, 928-935.
²V. Amstutz, K. E. Toghill, F. Powlesland, H. Vrubel, C. Comninellis, X. Hu, H. H. Girault, Energy Environ. Sci., 2014, 7, 2350-2358.
³V. Amstutz, K. E. Toghill, C. Comninellis, H. H. Girault, International Pat., WO 2013131838, 2013
⁴H. Vrubel and X. L. Hu, Angew. Chem., Int. Ed., 2012, 51, 12703-12706

When coupled to renewable but nonetheless intermittent power sources such as wind or solar, polymer electrolyte membrane (PEM) electrolyzers are intended to be in operation for tens of thousands of hours [1]. Hence, the long-term behavior of membrane electrode assemblies (MEAs) under these power operating characteristics is of great importance. Previous durability studies have focused on electrolyzers operating at constant current input. Commercial PEM electrolyzers show little to no significant degradation (<4µVh) after 40.000 h at moderate conditions (around 50°C and 1,3 A/cm²)[2]. In another study, constant and highly variable operation modes were compared for three used stacks after 7.500 h. It indicates that variable operation might result in higher cell decay [3]. To the best of our knowledge, no durability data has been published yet, that fundamentally contrasts the effects of defined dynamic load profiles and constant operation on the cell durability.
In this study we demonstrate for the first time, the different effect of a constant and defined dynamic operation on the cell decay. For this purpose, durability tests were performed using state-of-the-art PEM electrolysis cells. The cells were run for 1000h at 80°C, current densities up to 2 A/cm², and under constant and dynamic operation including startup and shutdown cycling. Dynamic hydrogen reference electrodes were incorporated to each MEA in order to separate the cathodic and anodic contributions to the overvoltage, and precisely identify the component undergoing degradation. Electrochemical impedance spectra and polarization curves were recorded along the tests and the water purity was also monitored. Post mortem analyses of the MEAs were conducted using EDX, SEM and TEM analysis to identify the degradation phenomena.
Our results show an effect of the operation mode on the degradation rate. Moderate conditions of 1 A/cm² show no significant degradation after 1000h. This is in line with the above mentioned results for commercial electrolyzer units. At higher current densities significant degradation rates were found. The impedance spectra indicate an increase in the cell resistance with elapsed time, and the reference electrode measurements indicate an increase in both anodic and cathodic overvoltage. We speculate that both corrosion of the porous sinter and deactivation of the electrocatalysts are responsible for the overall degradation at constant high current density operation. Our findings also indicate that dynamic cycling ensures less degradation even at higher current densities compared to the constant operation. This study undeniably suggests coupling PEM electrolyzers to intermittent power sources, contributing to transformative knowledge in the field of energy conversion and storage.
[1] M. Carmo et al., J of Hydrogen E., 38, 4901 (2013)
[2] Katherine Ayers, presented at DOE Fuel Cell Technologies Webinar, May 23, 2011
[3] 2013 Annual Merit Review Proceedings, II.A.2

Alkaline water electrolysis is a long-established and well matured technology for producing hydrogen on a commercial scale. Due to its reliable, safe, significant efficient operation, and good life-time characteristics (reaching up to 20 years), it constitutes the most extended technology at a commercial level worldwide, for the production of electrolytic hydrogen. As an example, by 1902, more than 400 industrial alkaline water electrolysers were in operation. In the 1920 and 1930s, a number of different electrolysers were developed, primarily for the ammonia fertilizer production based on low-cost hydroelectricity¹. Nowadays, to expand the use of water electrolysis, especially when coupling to renewable energy sources, it is mandatory to reduce energy consumption, cost, and maintenance of current electrolyzers, and, on the other hand, to increase their efficiency, durability, and safety². A crucial component inside the electrolysis cell is the separating membrane or diaphragm that prevents the mixing of the produced gases, in order to avoid the risk of an explosive mixture being formed in the electrolysis unit. However, even to this date, commercial alkaline systems use very thick (0.5-4 mm) oxide (ZrO₂, NiO₂) materials, or even carcinogenic asbestos materials as diaphragms. Hence, advanced membranes and separator materials developed for other technologies in the last decades have a great potential when applied in classic alkaline electrolysis, in order to drastically improve its characteristics and minimize the drawbacks of using conventional separator materials. In this study, a complete series of modern membrane materials were investigated for hydrogen production in alkaline water electrolysis cells. The physico-chemical characteristics were comprehensively addressed and the main process constraints (e.g., electrical, reaction, and transport) were analyzed. Exceptional improvements could be demonstrated using new membrane materials enhancing performance, gas separation, and the operation at higher pressures have also been proven to be achievable.
[1]. J. Mergel, M. Carmo and D. Fritz. Transition to Renewable Energy:Status on Technologies for Hydrogen Production by Water Electrolysis, D. Stolten, V. Scherer, Editors, p. 423-450, Wiley-VCH, Weinheim (2013)
[2]. M. Carmo, D. Fritz, J. Mergel and D. Stolten, International Journal of Hydrogen Energy, 38, 4901-4934 (2013)

Water electrolysis emerges as key technology for the long-term storage of renewable energy sources.[1,2] Hereby, PEM electrolyzers have the greatest potential, due to low ohmic losses, low kinetic overpotentials and good partial load range, achieved by the proton exchange membrane.[3] One of the biggest challenges connected with PEM electrolyzers is to provide improved anode catalysts (anode: oxidation of water to oxygen, oxygen evolution reaction OER) which offer high catalytic activity and stability against corrosion at minimal noble metal content. With respect to the materials properties, Ir oxide is the best OER catalyst combining activity and stability.[4] However, Ir is scarce and therefore its content in the catalyst has to be reduced to a minimum, while conserving its beneficial materials properties.
Concepts for lowering the Ir content can be adopted from fuel cell catalysis, where alloy core-shell catalysts yielded improved activity at reduced noble metal (Pt) content.[5] In a typical core-shell nanoparticle catalyst, Pt is alloyed with a less noble and less expensive metal, like for instance Ni, which is leached out during electrochemical dealloying from the outmost layers to form a Pt shell and an alloy core. The electrocatalytic activity can then be tuned, for instance, by choice and content of the less noble metal.
Adopting this concept for water electrolysis, we have synthesized well defined Ir-Ni mixed oxides as thin films on Ti substrates. Depending on the initial Ni content, the Ir-Ni oxides offer excellent OER activity and outperform pure Ir oxide as anode material, despite the fact that the Ir content was significantly decreased. Under OER reaction conditions Ni is partially leached out, however, significant amounts of Ni remain in the oxide layer after the OER, altering the Ir oxide properties.
To explore the origin of the increased OER activity, we have utilized a number of physicochemical characterization techniques, like SEM, EDX, TEM, XRD, ICP-OES, XPS and TPR, leading to a fundamental understanding of structure and chemical state of the oxide films before and after the electrocatalytic OER. Correlating these results to the electrocatalytic OER performance we are able to identify major factors determining the OER activity.
References
[1] T. Reier et al., J. Electrochem. Soc. 2014, 161, F876
[2] H. Dau et al., ChemCatChem 2010, 2, 724
[3] M. Carmo et al., Int. J. Hydrogen Energy 2013, 38, 4901
[4] T. Reier, M. Oezaslan, P. Strasser, ACS Catal 2012, 2, 1765
[5] P. Strasser et al., Nat. Chem. 2010, 2, 454-459

The challenge in electrocatalytic water splitting, which hinders the application of devices to convert sunlight or electricity into storable fuels, is the anodic multi-electron oxygen evolution reaction (OER) with its extremely sluggish surface kinetics.¹ Polymer electrolyte membrane (PEM) electrolyzers show advantages compared to alkaline electrolyzers in terms of compact system design, operating at high current densities with high voltage efficiency, and providing high gas purity,² however, they require large amount of noble metals (e.g., Ru and Ir for OER).^2,3 Compared to highly active but unstable RuO_x, IrO_x is a catalyst of choice due to its comparable activity and high stability.⁴ However, due to the scarce nature of Ir, novel strategies are critically needed to further reduce the amount of Ir in OER catalysts. One strategy is to use suitable corrosion-resistant supports; another is to design IrMO_x core-shell nanoparticles (NPs),⁵ where M represents an inexpensive abundant transition metal that helps to tune the intrinsic activity and significantly lower the noble metal content by concentrating Ir in a thin shell of the NPs.
Here, we present a combination of both strategies. Antimony doped tin oxide (ATO) bulk powder with high surface area (164 m²/g) was synthesized as corrosion resistant support. IrNi metallic NPs⁵ were then synthesized and immobilized on ATO. ATO supported IrNiO_x core-shell structure was formed using electrochemical selective dealloying of Ni and a consecutive surface oxidation. Bulk and surface compositions, morphology, IrNi-ATO interaction, OER electrocatalytic activity and stability relation were established using physicochemical characterization techniques ICP-OES, XRD, STEM, EDX, XPS, and electrochemical measurements. ATO supported IrNiO_x core-shell catalysts exhibited approximately 2.5 fold enhancement in Ir-mass based OER activity compared to carbon supported Ir NPs in acidic media. Moreover, the core-shell catalysts showed an improved stability compared to carbon supported pure Ir. This study documents the successful synthesis of IrNiO_x core-shell NPs supported on high surface area ATO with excellent OER performance in acidic medium, pointing out a path forward to nanostructured PEM electrolyzer electrodes with dramatically reduced noble metal content.
References
(1) Dau, H.; Limberg, C.; Reier, T.; Risch, M.; Roggan, S.; Strasser, P. ChemCatChem2010, 2, 724.
(2) Carmo, M.; Fritz, D. L.; Mergel, J.; Stolten, D. Int. J. Hydrog. Energy2013, 38, 4901.
(3) Song, S.; Zhang, H.; Ma, X.; Shao, Z.; Baker, R. T.; Yi, B. Int. J. Hydrog. Energy2008, 33, 4955.
(4) Reier, T.; Oezaslan, M.; Strasser, P. ACS Catalysis2012, 2, 1765.
(5) Nong, H. N.; Gan, L.; Willinger, E.; Teschner, D.; Strasser, P. Chemical Science2014, DOI: 10.1039/C4SC01065E.

Electrochemical formation of chemical bonds provides a convenient and energy dense mode of providing and storing electrical energy efficiently. Catalysts for oxygen electrochemical processes, including the oxygen reduction reaction (ORR) and oxygen evolution reaction (OER), are critical for the commercial viability of renewable energy storage and conversion devices such as fuel cells, artificial photosynthesis, and metal-air batteries. Transition metal oxides are an excellent system for developing cheap, non-noble-metal-based catalysts, especially for the OER.
Central to the rational design of novel catalysts is the development of quantitative structure-activity relationships (QSARs), which are relationships that correlate the desired catalytic behavior to structural and/or elemental properties of materials. The ultimate goal is to then use these relationships to guide materials design. The perovskite oxide family (AA&’BB&’O3, where A and A&’ are generally an alkaline-earth or rare-earth metal and B and B&’ are transition metals) is a versatile class of materials with a wide-range of chemistries and physical properties, making it ideal for systematic analysis of QSARs. In this report, 101 samples of 51 perovskites were compiled from our group&’s experimental work, in addition to 5 studies from literature. The predictive accuracies of different linear regression models were assessed using 23 variables describing the oxide structure (e.g. tolerance factor, bond lengths, bond angles, etc.) and elemental atomic structure (transition metal oxidation state, number of electrons, etc.), including simple least squares regression, multiple least squares regression, stepwise regression, penalized methods, and principal components regression. The coefficients of the highest performing models were used to identify and rank the strength of the 23 predictors. It was found that a large fraction of the variables need to be considered in order to develop strong predictive relationships, largely outperforming models based only on a single descriptor (as is conventionally done in the field). The study identifies several important descriptors that have stronger correlations with OER activity than those described to date.

In-situ studies of electro-catalysts are of high interest since they offer the opportunity to study their atomic and electronic structure in their active state. We present environmental transmission electron microscopy (ETEM) and X-ray near edge absorption spectroscopy (XANES) studies of O₂ evolution catalysis during H₂O splitting based on Pr-doped CaMnO₃ (PCMO) perovskite electro-catalysts. These systems offer the opportunity for fundamental studies of the role of variable Mn valence state, surface structure and defect chemistry for multi-step charge transfer reactions.
ETEM studies of electro-catalytic water splitting are a great challenge, since electro-catalytic activity must be separated from beam-induced effects. In addition, gas phase reactions of H₂O and intermediates at the catalyst surface are difficult to be captured. Here, we show that the electron beam can be used as a tool for generating a positive potential at the PCMO electrodes due to secondary electron emission. The positive potential in the order of 1-2 V can used to drive oxidation reactions at the electrode such as oxygen intercalation at an oxygen deficient surface structure as well as oxygen evolution from water splitting. The finding of a beam induced positive potential is supported by off-axis electron holography combined with electrostatic modelling of the observed phase shifts. First steps towards electro-chemical control of the catalyst are performed using a Nanofactory STM-TEM holder and applying an electric bias to the TEM sample.
One of our central findings is that at positive potential in the active state, the electro-catalyst fundamentally changes surface morphology and atomic surface structure in contact with water vapor [1].
Electron energy-loss (EEL) spectra [1] as well as in-situ XANES data [2] reveal that the Mn valence is decreased in the active state due to oxygen vacancy formation, contrary to the expectation of electrode oxidation at positive potential. Careful TEM analysis of samples measured by ex-situ cyclic voltammetry and in-situ bias-controlled ETEM experiments allow us to distinguish between self-formation of the active state during oxygen evolution and corrosion processes at the Pr_1-xCa_xMnO₃-H₂O interface. We can correlate trends in O₂ evolution activity and defect chemistry in the active state to doping induced changes of the electronic band structure in A-site doped manganites.
[1] S. Raabe, D. Mierwaldt, J. Ciston, M. Uijttewaal, H. Stein, J. Hoffmann, Y. Zhu, P. Blöchl, and Ch. Jooss, Adv. Funct. Mater. 22 (2012) 3378-3388.
[2] D. Mierwaldt, S. Mildner, R. Arrigo, A. Knop-Gericke, E. Franke, A. Blumenstein, J. Hoffmann and Ch. Jooss, Catalysts 4 (2014) 129-14

Active, stable and cost-effective electrocatalysts for oxygen evolution reaction (OER) and hydrogen evolution reaction (HER) are key to water splitting for H₂ production through electrolysis. Here, we will discuss about an advanced NiFe layered double hydroxide (NiFe LDH) OER electrocatalyst with better performace than Ir benchmark and nanoscale NiO/Ni hetero-structures formed on carbon nanotube sidewalls (NiO/Ni-CNT) as highly effective electrocatalysts with HER catalytic activity similar to Pt. The high OER activity of NiFe LDH is contributed by the LDH phase and ultrathin nanoplate morphology highly accessible to the electrolyte, and the high HER activity of NiO/Ni-CNT is attributed to NiO/Ni nano-interfaces formed by low-pressure thermal decomposition of Ni(OH)₂ precursors bonded to CNT sidewalls. The Ni²⁺-CNT interactions impede complete reduction and Ostwald ripening of Ni species into the less HER active pure Ni phase. A water electrolyzer pairing up NiFe LDH and NiO/Ni-CNT could achieve ~20 mA/cm² at a voltage of 1.5 V and ~100 mA/cm² at a voltage of 1.58 V under room temperature. The low voltage allows the electrolyzer to be operated by a single-cell 1.5 V alkaline-battery, which is achieved for the first time by using cheap, non-precious metal based electrocatalysts.

Metal nanoparticle arrays (MNAs) have unique properties due to their sizes and geometries, and they differ significantly from the individual atoms and the bulk material. MNAs are widely used for many applications including the fabrication of materials with enhanced optical, magnetic, plasmonic, and mechanical properties. MNAs have attracted a lot of research interest in the field of catalysis for fuel cell applications. The formation of catalytic nanoparticle systems will have a significant impact in advancing the life and total efficiency of fuel cells such as proton exchange membrane fuel cells (PEMFC) where the electrocatalytic properties of Pt is being explored. The conventional techniques used to fabricate MNAs usually involve lithographic techniques; however, these processes are sophisticated and time consuming, and the formation of sub-50-nm nanoparticle sizes has become increasingly difficult. Recently, Au nanoparticle array has been successfully prepared on dimpled Ta substrate using thermal dewetting; however, the major setback associated with this method is the deformation of both the substrate and metal thin films when applied to high-melting point metals such as Pt. Pulsed laser dewetting is able to generate well-defined MNAs of both low and high melting point metals with the unique advantage of very little or no thermal damage to the substrate. Within the short incident time of the laser pulse, typically in the range of 7-12 ns, the laser energy is instantaneously converted into heat, and if the generated heat is beyond a metal&’s melting point threshold, the metal thin film is dewetted with minimal or no heat transfer to the underlying substrate. We report here the results from our study on the formation of Pt MNAs using laser dewetting of Pt thin films sputter-deposited on DT substrate under high vacuum condition. The DT substrate was fabricated using electrochemical anodization in highly concentrated H₂SO₄/HF solution. It has been demonstrated that dewetting occurs only at and beyond the threshold fluence. Beyond this threshold a single laser pulse was enough to achieve complete dewetting. The effect of several key parameters, including laser fluence, irradiation time, and film thickness, on the nanoparticle sizes and their distribution was studied. To better characterize the MNA features, the percentage of dimples occupied by Pt nanoparticles was determined. As high as 80% of dimpled Ta occupancy can be achieved using pulsed laser dewetting. This study shows that laser dewetting is a novel method capable of annealing thin films of high-melting point Pt metal to achieve well-defined MNAs with narrow particle size distribution without subsequent damage to the DT substrate.

Bimetallic nanocrystals (NCs) enclosed by high-surface energy facets have been of enormous interest due to their pronounced catalytic performance in numerous chemical and electrochemical reactions. However, it remains a significant challenge to develop a facile method to synthesizing bimetallic NCs with high-surface energy facets in the form of finely-tuned structures due to the difficulties in manipulating the nucleation and growth kinetics of NCs in the presence of multiple metal precursors. In the present work, a facile one-pot aqueous synthesis method is developed for the production of bimetallic Au@Pd core-shell NCs with an unusual truncated hexoctahedral (THOH) shape without pre-synthesized seeds. The THOH Au@Pd NCs are bound by multiple high- and low-index facets. The formation of this unique structure is realized through the co-reduction of Au and Pd precursors under precisely controlled kinetic conditions. The prepared THOH NCs exhibit a prominent electrocatalytic performance for ethanol oxidation, which is attributed to their characteristic structural features. This study significantly expands the understanding of NC growth and will lead to fabricating novel nanomaterials with desired morphologies and functions.

Ionomers are high performance polymers in which the mechanical and electrical properties are controlled by the mesoscopic clustering of a small molar fraction of ionic groups [1]. Perfluorosulfonic acid membranes such as Nafion represent a remarkable advance in polymer membrane technology owing to its outstanding electrochemical and mechanical properties. Nafion α#8209;relaxation has been the subject of intense investigations since it regulates the performance of electric actuators and polymer electrolyte fuel cells. The α#8209;relaxation temperature is the underlying parameter to control Nafion shape/temperature memory effects and the PEFC performance at high temperature. However, the overriding mechanism of α#8209;relaxation is not fully understood and has imposed a challenge to various research groups for the last 30 years [2].
In this work, dielectric spectroscopy and atomic force microscopy measurements of Nafion membranes allowed identifying the conformation transition of the polymeric aggregates as the process underlying the αshy;#8209;transition. The α#8209;relaxation was shown to be due to the longitudinal polarization of condensed counterions in the vicinity of anionic groups distributed along the polymer backbone. The dependence of this relaxation on the frequency reflects conformation changes of the polymer backbone. At high temperatures the α#8209;relaxation displaces to lower frequencies indicating the elongation of the Nafion polymer aggregates. In addition, the dielectric spectroscopy study of ionomers offered new insights to the understanding of the statistical distribution of ionic groups along the main chain. The morphological transition was confirmed by atomic force microscopy, which revealed elongated domains in the samples annealed at high temperature.
Acknowledgments
Thanks are due to the Brazilian funding agencies (CAPES, CNPQ, FAPESP) and also to CNEN. This work was also realized with the financial support of the Natural Sciences and Engineering Research Council of Canada and the Canadian Foundation for Innovation.
References
[1] K. A. Mauritz, R. B. Moore, Chem. Rev., 2004, 104, 4535.
[2] K. A. Page, K. M. Cable, R. B. Moore, Macromolecules, 2005, 38, 6472.

Poly(4&’-phenoxybenzoyl-1,4-phenylene) (PPBP) is a one of the most versatile super engineering plastics, and the introduction of functional groups to PPBP is a promising strategy for bringing multiplicity in terms of electrochemical applications such as polymer electrolyte fuel cell membranes. However, it is generally difficult to synthesize high molecular weight polymers having sufficient film formability from functionalized monomers. Therefore we studied the synthesis of borylation of high molecular weight PPBP and converting the boronic acid groups of borylated PPBPs (B-PPBPs) into the functional groups such as sulfonic acid groups via Suzuki-Miyaura coupling reaction for post-functionalization, in order to synthesize useful functionalized polymers as polymer electrolyte fuel cell membranes. PPBP (M_n = 74 kg mol^-1, M_w/M_n = 2.3) was synthesized by Ni(0)-catalyzed coupling polymerization. The obtained PPBP was reacted with bis(pinacolato)diborane (B₂pin₂) in tetrahydrofuran (THF) by using di-mu;-methoxo bis(1,5-cyclooctadiene) diiridium ([Ir(OMe)(COD)]₂) and 2,2&’-bipyridyl (bpy) at 40 0C for 12 h under Ar atmosphere. B-PPBP was identified from ¹H NMR, GPC, and FT-IR. The ¹H NMR spectra of B-PPBP exhibited a distinctive new resonance peak of the methyl group of Bpin attached to the polymer at 1.0-1.3 ppm. In the FT-IR spectra of B-PPBP, the stretching vibration of B-O groups was observed at 1355 cm^-1. The weight average molecular weights (M_w) and introduction rates of Bpin increased with decreasing the amount of THF, and we obtained B-PPBPs having a high introduction rate up to 131%. We introduced various functional groups to the synthesized B-PPBP (M_n = 92 kg mol^-1, M_w/M_n = 2.6, Bpin = 90%) via Suzuki-Miyaura coupling. Functional groups such as amino group, aldehyde, cyano, and methoxy groups were reacted with B-PPBP in the presence of Pd catalyst. We confirmed from the ¹H NMR spectra that the Suzuki coupling reaction successfully proceeded. The introduction rates of amino groups, aldehyde groups, cyano groups, methoxy groups were 93%, 42%, 99% and 76%, respectively. We also attempted the introduction of sulfonic acid group using a similar Suzuki-Miyaura coupling method. B-PPBP (M_n = 230 kg mol^-1, M_w/M_n = 3.4, Bpin = 50%) and 3,5-dimethylphenyl 4-bromobenzensulfonate ester (S1) were used for the synthesis. Introduction of S1 to PPBP (S1-PPBP) was identified from ¹H NMR, FT-IR, and elemental analysis. The introduction rate of sulfonic groups identified from the ¹H NMR was 81%. The FT-IR spectra of S1-PPBP exhibited that the stretching vibration of B-O groups at 1355 cm^-1 decreased. The ion-exchange capacity which determined from elemental analysis was 1.40 meq g^-1. These results suggest that the successful introduction of functional groups facilitates the synthesis of hydrocarbon-type polymer electrolytes.

The advancement in green energy conversion systems such as fuel cells is important for the improvement of quality living and environmental sustainability. A major challenge with most existing catalysts for fuel cells is that they are extremely high cost due to use of high loading of noble metals and are subject to degradation over time due to dissolution of metals in fuel cell operation conditions. While palladium and platinum exhibit very high electrocatalytic activities, they are scarce and expensive. From industrial perspective, alloying them with earth abundant transition metals such as nickel, copper, etc. could reduce the cost of the catalyst production significantly. Fundamentally, alloying metals can change electrocatalytic properties in significant ways so that the nanoalloy catalysts can outperform the pure platinum or palladium catalysts. This presentation will discuss recent findings of our investigation of the synthesis of palladium-nickel nanoalloys, focusing on the controllability of the size, shape, composition and structure of the alloy nanoparticles. The preliminary results show that palladium-nickel nanoparticles with narrow size distribution and controllable bimetallic composition can be synthesized by controlling the synthetic parameters. The results from detailed morphological and structural characterizations of these nanoalloys will also be discussed, attempting to establish the correlation with their electrocatalytic performance characteristics in fuel cell reactions.

The ability to control nanoscale alloying and phase segregation properties is important for the exploration of multimetallic nanoparticles for the design of advanced functional materials for chemical sensors and sustainable energy production, conversion, and storage. While noble metal nanoparticles have been widely explored, their high costs and limited global supplies do not meet the ever-increasing demand of sustainability. The alloying copper into noble metal nanoparticles provides an alternative to address the problem, in addition to exhibition of the unique nanoscale properties different from the pure metal counterparts. In this report, we highlight recent insights into the nanoscale phase properties of copper-based alloy nanoparticles synthesized by wet chemical processes. Examples include gold-copper (AuCu) and palladium-copper (PdCu) nanoparticles. The characterizations of these nanoparticles using ICP-OES, TEM, XRD, and HE-XRD techniques have shined some light on the importance of changes in physical and chemical properties for the nanoscale alloying. These findings are important for understanding the synthetic parameters governing the structure and activity of the nanoalloys for the design of low-cost and multifunctional catalysts for applications in sustainable energy.

Recently, there has been a push towards the synthesis and study of nanoparticle catalysts comprising of non-precious metals; particularly those of M-Pt composition due to increasing costs, decreasing reserves, and the environmental impact of other fuels. The involvement of a non-precious metal increases the electrocatalytic activity as well as decreasing the cost for such reactions and commercial uses as automobile hydrogen fuel cells. In this work, we synthesize a series of multi-metallic nanocatalyst of Pd-Ni-Pt sandwich composition in order the study the effect strain has on their electrocatalytic ability in methanol oxidation reaction (MOR) and formic acid oxidation reaction (FOR). Through cyclic voltammetry and chronoamperometric measurements, the different catalysts activity and stability can be studied to show an increase in overall activity and stability by the addition of a non-precious metal, Ni. Both acidic and alkaline conditions were used to obtain a more thorough understanding of the catalyst system. Through this model system, the effects of strain imparted by multi-metallic core-shell particles can be studied in how it affects the catalytically active surface and increases the activity for future fuel cell works.
Sneed, B.T.; Young, A.P.; Jalalpoor, D.; Golden, M.C.; Mao, S.; Jiang, Y.; Wang, Y.; Tsung, C.K. Shaped Pd_Ni_Pt Core-Sandwich-Shell Nanoparticles: Influence of Ni Sandwich Layers on Catalytic Electrooxidations. ACS Nano. Article ASAP.

Sulfonated aromatic polymers have been widely studied as polymer electrolyte membrane (PEM) materials for fuel cell applications. However, the mechanical and dimensional stability are insufficient under humidified conditions due to their high ion exchange capacities (IEC). Therefore, it is necessary to achieve both high proton conductivity and low water uptake for sulfonated aromatic polymers. To maintain high proton conductivity without decreasing mechanical properties under humidified conditions, we have focused on block copolymers consisting of hydrophilic and hydrophobic segments, which are expected to form continuous ionic channels by a micro-phase separation. In this study, we synthesized multiblock copolymers consisting of hydrophilic sulfonated poly(4-phenoxybenzoyl-1,4-phenylene) (S-PPBP) and hydrophobic poly(arylene ether ketone) (PAEK), and their mechanical and electrochemical properties were investigated.
The sulfonated monomer, 2,2-dimethylpropyl-4-[4-(2,5-dichlorobenzoyl)phenoxy]benzene- sulfonate (NS-DPBP), and the hydrophobic oligomer, dichloro-terminated poly(arylene ether ether ketone6H) (PAEK6H-Cl), was polymerized via nickel-catalyzed coupling polymerization to obtain the copolymers (S-6H(n)x:y) with varying the composition ratio. The n indicates the unit length of hydrophobic oligomer, and the x:y indicates the chemical composition ratio of S-PPBP:PAEK. The weight-average molecular weights of S-6H(7)3:1, 2:1, and 1:1 were 1.54 x 10⁵, 1.80 x 10⁵, and 7.55 x 10⁴ g mol^-1, respectively. The IEC values of S-6H(7)3:1, 2:1, and 1:1 were 1.86, 1.63, and 1.24 meq g^-1, respectively. As the IEC decreased, the mechanical properties and dimensional stabilities were significantly improved due to suppressing the water uptakes. The introduction of hydrophobic PAEK6H block into the polymer electrolyte structure by block copolymerization was effective to obtain suitable mechanical properties under humidified conditions for fuel cell applications. S-6H(7)3:1 and 2:1 membranes showed a high proton conductivity of over 10^-1 S cm^-1 at 80 0C and 90%RH in spite of their low IEC values. This result suggested that S-6H formed a micro-phase separation that was an effective water transport pathways.
Acknowledgements
This work was financially supported by the New Energy and Industrial Technology Development Organization (NEDO).

The catalyst layer of membrane electrode assemblies (MEAs) are composed of an ionomer and catalyst. The ionomers are required to have high ionic conductivity and high fuel gas permeability. Since there are no suitable hydrocarbon ionomers used for catalyst layers, Nafion solution is used in most cases. It is, however, desired to use hydrocarbon ionomers for catalyst layers in view of the decrease in cost and burdens of environment. Since amphiphilic diblock copolymers show a microphase separation, they are expected to work as ionomers of catalyst layers. In this study, poly(phenylene)-type amphiphilic diblock copolymers were synthesized, and their electrochemical properties were evaluated. Poly(phenylene)-type dibock copolymers (NSPr_mH_n) were synthesized by the polymerization of 1,4-dibromo-2,5-di-[4-(2,2-dimetyl-propoxysulfonyl)phenyl]proxybenzene (NS-DBPrB) and 1,4-dibromo-2,5- dihexyloxybenzen (DBHB) via catalyst transfer polycondensation. The m and n mean the polymerization degree of the hydrophilic and hydrophobic units. The number-average molecular weight and molar-mass dispersity of NSPr₂₈H₄₃ was 30.3 kg mol^-1 and 1.17, respectively. SPr_mH_n was synthesized by the deprotection of neopentyl groups of NSPr_mH_n with diethylamine hydrobromide. The ion exchange capacity (IEC) value of SPr₂₈H₄₃ was determined by elemental analysis to be 2.29 meq g^-1. The MEA was fabricated with a NR211 membrane, SPr₂₈H₄₃ ionomer for cathode, and Nafion^#9415; ionomer for anode by hot-press at 130 0C for 10 min. The electrochemically active surface area (ECA) values were derived from cyclic voltammograms. The ECA value was 36 m² g^-1 at 80 0C and 100%RH. The ECA values decreased as relative humidity decreased. Impedance measurements were carried out by using an impedance analyzer to evaluate the charge transfer resistance of the MEAs. While the charge transfer resistance of the MEA with SPr₂₈H₄₃ ionomer for cathode was the lowest value at 70 %RH and 80 0C, the MEAs showed a higher charge transfer resistance at high relative humidity conditions, probably due to flooding. The membrane resistance of the MEAs decreased as relative humidity decreased. The PEFC performance of the MEA was evaluated at 80 0C and 0.1MPaG in the range of 30 - 100%RH. The limiting current density was 1,920 mW cm^-2, and the maximum power density was 579 mW cm^-2 at 80 0C and 80%RH. Acknowledgements This work was financially supported by the New Energy and Industrial Technology Development Organization (NEDO).

The ability to nanoengineer the composition and structure of noble-metal based alloy catalysts is important for achieving active, robust and low-cost catalysts for fuel cell applications. A key to this ability is the fundamental understanding of the alloy composition regulated electrocatalytic synergy. In this work, selected palladium-based nanoalloy catalysts have been exploited as a model system for electrocatalytic oxygen reduction reaction (ORR). In order to maximize the catalytic activities of Pd-based nanoalloys, the control of the morphology and the composition is very important. This report discusses the recent findings of an investigation of carbon-supported PdNi nanoalloy electrocatalyts with different Pd/Ni ratios for ORR in acidic electrolyte. The electrocatalytic data based on measurements of electrochemically active area (ECA) and mass activity/specific activity (MA/SA) have shown a clear dependence on the binary composition of the as-prepared nanoalloys and the composition change of the catalysts under the electrochemical condition. The effect of alloying and de-alloying on the electrocatalytic activity will also be discussed in terms of the detailed structural evolution of the nanoalloy catalysts which are probed by high-energy X-ray diffraction characterization.

We describe a lab-in-a-shell strategy for the preparation of multifunctional core-shell nanospheres consisting of a core of metal clusters and an outer microporous silica shell. Various metal clusters (e.g., Pd, Pt, Cu and Co) were encapsulated and confined in the void space mediated by the entrapped polymer dots inside hollow silica nanospheres acting firstly as complexing agent for metal ions and additionally as encapsulator for clusters, limiting growth and suppressing the sintering.¹ The Pd clusters encapsulated in hybrid core-shell structures exhibit exceptional size-selective catalysis in allylic oxidations of substrates with the same reactive site but different molecular size (cyclohexene ~0.5 nm, cholesteryl acetate ~1.91 nm). The solvent-free aerobic oxidation of diverse hydrocarbons and alcohols was further carried out to illustrate the benefits of such an architecture in catalysis. High activity (Tetralin, turn over frequency: 469 h^-1; Benzyl Alcohol, ~40000 h^-1; Octan-2-ol, 417 h^-1), outstanding thermal stability (up to 600 ^oC) and good recyclability (reusing twenty times) were observed over the core-shell nanocatalyst.
Acknowledgment: Research sponsored by the Office of Basic Energy Sciences, U.S. Department of Energy.
1 Qiao, Z. A.; Huo, Q. S.; Chi, M. F.; Veith, G. M.; Binder, A. J.; Dai, S. Adv. Mater. 2012, 24, 6017.

Performance of direct ethanol fuel cell adopting Pd-MoO₂/C as electrocatalyst for the anode oxidation
Liu Qingming^#9332;*; Yu Hongying^#9333;; Zhou Debi^#9333;
#9332; School of Chemistry and Materials, University of Science and Technology of China, Hefei, China.
#9333; School of Chemistry and Chemical Engineering, Central South University, Changsha, China.
*E-mail: [email protected]
Pd-MoO₂/C was successfully synthesized via intermittent microwave heating-glycol reduction method and it was adopted as the electrocatalyst for the ethanol oxidation in the anode of direct ethanol fuel cell (short for DEFC). The performance of Pd-MoO₂/C was measured by cyclicvoltammetry (CV) and chronoamperometry (CA). The results revealed that Pd-MoO₂/C possessed excellent activity and stability for the electrochemical oxidation of ethanol in alkaline medium. By adopting the foamed nickel containing Pd-MoO₂/C as anode and MnO₂/C as air electrode respectively, the single DEFC was designed by ourselves. The discharge performance of single DEFC was measured by the constant current discharge method. The DEFC group was also assembled. This DEFC group can lighten a bulb (2.5V, 0.3A) normally, and it can discharge continuously by adding ethanol into the anode tank at room temperature. This research made a progress on the application of DEFC.
Keyword: Electrocatalyst; Direct ethanol fuel cell; Ethanol oxidation; Constant current discharge method

Platinum is a key component of the catalysts used for the oxygen reduction reaction (ORR) in proton-exchange membrane fuel cells (PEMFCs). Despite its excellent performance in ORR, its high cost and low abundance in the earth&’s crust have created a major barrier for the large-scale commercialization of PEMFCs. An attractive strategy for reducing the Pt content while retaining the activity of a Pt-based catalyst is to deposit a few atomic layers of Pt on the surface of nanocrystals made of another metal. In particular, Pd is a good substrate for epitaxial deposition of Pt due to their close match in lattice constant. During deposition on Pd, however, the Pt atoms often take an island growth mode because of a strong bonding between Pt atoms. Here we report a versatile route to the epitaxial, conformal deposition of Pt as uniform, ultrathin shells on Pd nanocubes in a solution phase. Relatively slow introduction of the Pt precursor and high reaction temperature allowed the deposited Pt atoms to spread across the entire surface of a Pd nanocube to generate a uniform shell. The thickness of the Pt shell could be controlled from one to six atomic layers by varying the amount of Pt precursor added into the system. Compared to a commercial Pt/C catalyst, the Pd@Pt_nL (n=1minus;6) core-shell nanocubes showed enhancements in specific activity and durability toward the ORR. Density functional theory calculations on model (100) surfaces suggested that the enhancement in specific activity can be attributed to OH destabilization on the Pd@Pt_nL nanocubes, which facilitates OH hydrogenation, the rate-limiting step of the ORR. A volcano-type relationship between the ORR specific activity and the number of Pt atomic layers was derived, in good agreement with the experimental results. From both theoretical and experimental studies, the catalyst based on Pd@Pt_2minus;3L nanocubes exhibited highest specific activity toward the ORR. Due to the high electrochemical surface area and the enhancement in specific activity, the Pd@Pt_1L nanocubes showed a Pt mass activity with almost three-fold enhancement relative to the Pt/C catalyst.

Three-dimensionally ordered mesoporous carbon sphere arrays (OMCS) supported Pt nanoparticles (Pt/OMCS) were synthesized and studied as electrocatalysts for methanol oxidation reaction (MOR) and oxygen reduction reaction (ORR). The OMCS were prepared through a combination of hard- and soft-templating approaches. Silica inverse opal (hard-template) was used to mold the external shape of the carbon particles and amphiphilic triblock copolymer Pluronic F127 (soft-template) was used as the mesopore-directing agent. The OMCS supported Pt (Pt/OMCS) catalyst was prepared by loading Pt nanoparticles on the OMCS by hydrogen reduction method. In the prepared Pt/OMCS, the Pt particles with a mean size of ~1.6 nm are homogeneously dispersed on the mesopore walls of the carbon spheres. The Pt/OMCS catalyst exhibits smaller Pt particle size, greater Pt dispersion, larger specific electrochemically active surface area (ECSA), higher activity for MOR and ORR, and better electrocatalytic stability than the carbon black (Vulcan XC-72R) supported Pt and commercial Pt/C catalysts.

We report a highly improved kinetics with superior CO tolerance in an electrocatalytic methanol oxidation reaction (MOR) on platinum-mesoporous metal oxide composite thin films. Pt-mesoporous metal oxide composite films were synthesized by two-step process. First, mesoporous tin oxide thin films (MSnTFs) and mesoporous gallium oxide thin films (MGTFs) with wormlike structure were prepared by sol-gel method. And then, Pt is deposited into the pores of MSnTFs and MGTFs by using electrochemical deposition method.
In the results of electrochemical experiments as CO stripping and MOR, these samples showed the meaningful phenomena. Interestingly, we observed the high current pre-peak of CO stripping at 0.25 V, much lower potential than that of main peak, according to oxidation of weaker adsorbed CO molecules with Pt affected by mesoporous metal oxide thin film. In addition, these results were related to the explanations of effective enhancement of MOR. Pt-MGTFs and Pt-MSnTFs showed interesting MOR shape and much increased catalytic effiiency compared with only mesoporous Pt thin films. The properties of Pt-MSnTFs and Pt-MGTFs were characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM) and x-ray photoelectron spectroscopy (XPS) before and after deposition of Pt. From those analyses, we confirmed that strong metal support interaction (SMSI) between Pt and mesoporous metal oxides and significant changes of the electronic properties of Pt which could support the results of electrocatalytic activities.

The development of direct alcohol fuel cells (DAFCs) as a power source has drawn a surge of interest in recent years due to its high energy density, renewable biomass production likelihood, and ease storage and transportation. To enable effective electrochemical reduction of ethanol in a fuel cell, one of the major di#64259;culties is the Cminus;C bond cleavage for a complete oxidation of ethanol to CO₂, calling for the need of highly active, robust and low-cost catalysts. The development of effective strategies in nanoengineering the composition and structure of noble metal containing catalysts is an important pathway to address that difficulty. In this work, several new and refined nanoalloy catalysts have been prepared as catalysts for ethanol oxidation reaction. This presentation describes recent findings of an investigation of the correlation between the atomic scale structure and the electrocatalytic performance, aiming at providing a new fundamental insight into the role of the detailed atomic alloying and the interaction structure in the electrocatalytic mechanism. Major findings of the studies of binary and ternary nanoalloy catalysts will also be discussed to highlight the importance of controlling composition and structure for the design and preparation of the electrocatalysts.

The proton conductivity of graphene oxide (GO) nanosheet is known to be orders of magnitude greater than the bulk GO, thus it is essential to improve the dispersion of GO nanosheets in the proton exchange membrane (PEM) matrix to achieve higher conductivity. In this study, we reports a facile and effective method to fabricate a GO / sulfonated poly (ether ether ketone) (SPEEK) composite consists of various contents of GO nanosheets well-dispersed in SPEEK matrix by using electrospinning technique. The electrospun mats were then treated with solvent vapor or hot pressing to form a dense membrane for direct methanol fuel cell application. The composite membrane exhibits improved proton conductivity, water uptake, and mechanical properties due to the presence of the well-dispersed GO. It is believed that the GO nanosheets can not only induce continuous channels for proton-conducting via Grotthuss mechanism, but also act as methanol barriers to hinder the methanol molecules from passing through the membrane.

Direct methanol fuel cell (DMFC) has been considered as a powerful promising energy conversion system for a variety of portable applications, due to their effectiveness and cleanness. In a DMFC device, platinum materials are generally employed as anode catalysts due to their excellent performance in catalyzing the process of methanol dehydrogenation. In this work, surface roughed platinum (Pt) nanowires were fabricated by a galvanostatic electrodeposition method in a nanoporous template with increased current densities. The grain size and surface morphology of the Pt nanowires were studied by field emission scanning electron microscopy (FE-SEM), transmission electron microscopy (TEM), and X-ray diffraction (XRD). The experimental results showed that the surface of the Pt nanowires became rougher and the grain sizes were increased by increasing the electrodeposition current density. Compared to the smooth Pt nanowire catalysts, the surface roughed Pt nanowires presented better activity and higher durability for the methanol oxidation reaction. The rapid transport of electron or charge carriers can also be achieved through electrochemical impedance spectroscopy (EIS) measurement because Pt nanowires with rough surface have higher surface area with excellent conductivity. These surface roughed Pt nanowires are anticipated to find promising applications in many important fields such as catalysis and fuel cell.

In the polymer electrolyte fuel cells, Pt-based cathode catalysts have already been reported. Since Pt is expensive and rare material, researchers seek to develop Pt-free catalyst such as carbon alloys. High oxygen reaction (ORR) activities are reported in the carbon doped with nitrogen. Different chemical bonding structures, pyridinic-N, pyrrolic-N and graphitic N, exist in the graphite lattice. There is a disagreement on the most active site for ORR. Graphitic-like in zig-zag edge was reported as the most active for cathode catalysts by the first principle calculation [1], while very recently the pyridinic-N has been reported to play a key role in the activity [2]. In this study, electron beam exited plasma (EBEP) (reaction chamber pressure: 3 × 10^-4 Torr, electron beam acceleration voltage: 80 V, electron beam current: 3.5 A, negative bias voltage: -20 V) [3] has been firstly used for the N doping in HOPG. The surface is characterized by scanning tunneling microscopy (STM), X-ray photoemission spectroscopy (XPS) and Raman spectroscopy. To our surprise, the pyrrolic-N is preferably formed in the graphite lattice, which has never been observed by conventional doping method such as sputtering or ion gun. The time dependence of the C-N bonds formation is also investigated.
In the STM image of HOPG after irradiation of nitrogen plasma for 20 s, a radic;3 × radic;3 R30^° superstructure was formed, showing the formation of atomistic structures. In XPS spectra the presence of C-N bonds of graphitic (401.1eV), pyridinic (398.6 eV), and pyrrolic (399.6 eV) structures, were confirmed. In a previous report [4], Kondo et al. have found higher abundance ratio of pyridinic-N and graphitic-N, while in the present study a lower abundance ratio of pyridinic-N as well as graphitic-N was observed. The evolution of XPS intensity and Raman intensity of I_D/I_G revealed that the XPS intensity of pyrrolic-N and graphitic-N decreases with nitrogen plasma process time. Similar decrease was also observed from Raman intensity of I_D/I_G. The pyrrolic-N structures distorted six membered rings, therefore, the ratio of I_D/I_G increased. After 1 min irradiation, the pyrrolic-N structure decreased while the pyridinic-N structures started to increase. After 3 min irradiation, graphitic structures were disappeared and only pyridinic-N structure was observed. Thus the formation of each species of C-N bonds in the graphite structure changes its bonding characters depending on the process time.
[1] Ikeda et al., J. Phys. Chem. C 112, 14707 (2008).
[2] Chen et al., Chem. Commun. 50, 557 (2014).
[3] Ichiki et al., J. Plasma Fusion Res. 87, 682 (2011).
[4] Kondo et al., Phys. Rev. B 86, 035436 (2012).

Polymer electrolyte membrane fuel cells (PEMFCs), including direct methanol fuel cells (DMFCs), are emerging as promising candidates for the automobile industries and portable electronics due to their high power density and portability. However, the high cost due to noble metal based catalyst (e.g. Pt and Ru), and the low stability owing to corrosion of conventional carbon supports under chemical and electrochemical oxidation conditions have seriously hindered the commercialization of fuel cell technology [1]. Therefore, elaborate exploration and rational design of new materials of low cost, high efficiency and durability will have a significant impact on making these promising energy technologies commercially viable.
Titanium carbides and carbonitrides are expected to be good materials to replace carbon as electrocatalytic support, since they are chemically stable in acidic media and possess high electronic conductivity [2]. However, they eventually can be transformed to the titanium metal oxide, which is a thermodynamically stable compound at potentials higher than 0.9 V (vs RHE) in acidic media [1]. Taking advantage of this effect, the surface of TiC and TiCN supported platinum electrocatalysts has been modified by electrochemical activation, and the activity towards CO and methanol electrooxidation has been investigated.
In the present work, four different catalysts made of platinum nanoparticles supported on different materials (TiC, TiCN, TiN and C-black) were synthesised by the ethylene glycol method and mainly characterized by transmission electron microscopy (TEM), X-Ray diffraction (XRD) and X-Ray photoelectron spectroscopy (XPS). The activities of the catalysts and supports toward the CO and methanol electrooxidation reactions after two diverse activation treatments (cycling up to 0.9 V or up to 1.0 V versus RHE) were evaluated by cyclic voltammetry, chronoamperometry and in-situ Fourier transform infrared spectroscopy (FTIRS). A significant enhancement of the activity toward both reactions was observed for those carbide-based catalyst when the activation step arrived up to 1.0 V instead of 0.9 V. The mass activity for methanol oxidation of Pt/TiC_1.0V is 7 fold higher than Pt/TiC_0.9V and 2 folds higher than commercial PtRu/C catalyst. This catalytic enhancement is associated to the generation of oxygenated species onto the interphase sites of platinum and titanium carbide.
AKNOWLEDGEMENTS
This work has been supported by the Spanish Science and Innovation Ministry under projects CTQ2011-28913-C02-01 and CTQ2011-28913-C02-02. MR acknowledges to the FPU-2012 program.
1. Rabis, A., et al., Electrocatalysis for Polymer Electrolyte Fuel Cells: Recent Achievements and Future Challenges. ACS catalysis, 2012. 2(5): p. 864-890.
2. M. Roca-Ayats, et al., TiC, TiCN, and TiN Supported Pt Electrocatalysts for CO and Methanol Oxidation in Acidic and Alkaline Media. The Journal of Physical Chemistry C 2013, 117: pp 20769-20777.

Metal nanoparticles with well-defined structural characteristics serve as an important tool to probe the nature of heterogeneous catalysis. To date, researchers have uncovered many important factors governing the catalytic performance of nanoparticle catalysts, including composition, shape, size, surface/interface effects and so on. Despite these remarkable advances, it remains largely underexplored to apply the ripping nanotechnology to organic reactions, so as to improve the reactivity and selectivity of known reactions, and perhaps more importantly to enable organic reactions that are not readily accessible by homogeneous catalysis. In the first part of this talk we will introduce our new synthetic methods for various well-defined nanoparticles. In the second part, we will discuss how we exploited these syntheses towards obtaining catalysts with new activity and/or improved selectivity in a range of organic transformations.

Core-shell architectures have been proven beneficial in enhancing nanocatalysts&’ activity, selectivity and durability while increased utilization of precious metals such as platinum (Pt), an expensive but highly active catalyst for various electrochemical and chemical reactions, including the hydrogen oxidation reaction (HOR) and the oxygen reduction reaction (ORR) in proton exchange membrane fuel cells (PEFCs). In order to fully utilize benefits of this approach, a reliable synthesis method is essential to produce core-shell nanoparticles with uniform shell thickness tunable in 1 - 3 monolayer range. Usually the Pt monolayer shell is formed via electrochemical routes, such as galvanic displacement of an underpotentially deposited Cu layer.^[1] Here we report a surfactant-free, ethanol-based wet chemical approach to coating metal nanoparticles with uniform Pt atomic layers with high reproducibility and scalability. The principles applied in the coating method will be illustrated with two practical examples.
The first example is the ordered Ru-Pt core-shell nanoparticle electrocatalysts for the anodic HOR in PEFCs.^[2] Single crystalline core-shell particles are formed though Ru and Pt have distinctly different crystal structures, hexagonal close-packed (hcp) for Ru, and face-centered cubic (fcc) for Pt. The ordered lattice structural transition from Ru(hcp) to Pt(fcc) at the core-shell interface is verified by X-ray diffraction (XRD) and scanning transmission electron microscopy (STEM), coupled with density functional theory (DFT) calculations. The atomic structure of this electrocatalyst and the formation of Pt shell on Ru particles are examined using extended X-ray absorption fine structure (EXAFS) and X-ray absorption near edge structure (XANES). Furthermore, fuel-cell tests show that the Ru-Pt electrocatalysts with optimized structures and improved Pt utilizations exhibit enhanced activity and durability for the HOR.
The second example is Pt monolayer coated on Pd nanoparticles as electrocatalysts for the ORR, the cathodic reaction in PEFCs.^[3] The uniformity of Pt shells is verified by various characterization techniques, and DFT calculations also show that two-dimensional growth of Pt on Pd is energetically favorable. The as-prepared Pt monolayer electrocatalysts exhibit high electrocatalytic performance toward the ORR.
In conclusion, we have demonstrated a surfactant-free and high-yield chemical route for coating of Pt atomic layers on other metal nanoparticles, which ensures high reproducibility and scalability. The strategy illustrated here could be applicable to the fabrication of other bimetallic or multimetallic core-shell nanoparticles for various applications.
[1] R. R. Adzic, Electrocatalysis 2012, 3, 163-169.
[2] Y.-C. Hsieh, et al. Nat Commun 2013, 4, 2466.
[3] Y. Zhang, et al. ACS Catalysis 2014, 4, 738-742.

Fuel cell is an energy device that converts chemical energy to electrical energy. Because its controllable size and power, it is expected to be applied to various applications like household heating, engines for transportation, or power sources for mobile instruments. In low temperature-operating fuel cells in which the polymer electrolyte membranes are used, reducing the overpotentials of the electrochemical reactions at the electrode surface is a big issue. Oxygen reduction reaction at cathode significantly reduces the efficiency and the power of the fuel cell due to its slow reaction kinetics and oxidation reactions of small organic molecules like methanol and formic acid also take a part in activation loss of the fuel cell when the organic liquid fuels are used. To supplement the problem of conventional platinum catalyst, which is very expensive and vulnerable in the fuel cell operating condition, introducing other metal to make alloy or intermetallic compound has been widely used. The intermetallic compounds, which have ordered atomic arrays in contrast to the alloys, have high stabilities and activities for many electrochemical reactions. But, the intermetallic phases are generally formed at high temperature which can induce the severe sintering of nanoparticles. Although making small sized intermetallic nanoparticles can be a good way to develop a promising electrocatalyst, previous reports that synthesized the small sized intermetallic nanoparticles used tiresome and multi-step synthetic procedures. We developed a simple and unique method to synthesize the small sized intermetallic nanoparticles loaded on ordered mesoporous carbon/aluminosilicate by using block co-polymer induced one-pot assembly and incorporating aluminosilicate framework as an agent which strongly interacts with metal and suppresses the sintering of the nanoparticle at high temperature. The interaction between the loaded metal and aluminosilicate framework was studied by density functional theory calculation and model system experiments. The synthesized small sized intermetallic PtPb and Pt₃Co nanocatalyst exhibited an excellent activity and stability for the formic acid oxidation and oxygen reduction reaction, respectively, due to the characteristic of intermetallic phases and the high surface area. In this presentation, the detailed synthetic procedure and the effect of the strong metal-support interaction on the structure and catalytic activity of the catalyst will be explained.

One of the important obstacle that prevent fuel cell from replacing the internal combustion engine is the high polarization (mainly concentration polarization) and high cost of the catalyst (Platinum ) of the oxygen reduction reaction (ORR).Low temperature proton exchange fuel cells ( PEMFCs) are well known to be clean and efficient means for transport applications. This is due to the fact that PEMFCs are not only small in size and light in weight but they have high power densities at relatively low temperature. In an effort to reduce the cost of the catalyst, many research groups alloyed Pt with transition metals such as Ni and Co and produced a catalyst that use Pt.Ni or Pt.Co alloys to replace pure Pt and found that these alloyed catalyst produced ORR rate of reaction similar or sometimes better than the more expensive pure Pt. This effect was attributed to the formation of a special facet on the surface of Pt crystal that was called Pt (111) which has special catalytic activity. Her we show that transition metals like Ni and Co may act as a catalyst for the production of heterogeneous superhydrophobic surface in the carbon support (Vulcan XC72) containing Pt. This produced surface not only expands the triple phase boundary but also reduces mass transfer resistance and thus increases the rate ORR. Furthermore, it will be shown that the high concentration polarization which manifest itself by the appearance of limiting current density is due to the fact that the commercial Pt catalyst is very active and not sluggish ( oxygen surface concentration approaches zero quickly).The limiting current density is the maximum current that that can be obtained from the electrochemical reaction. The limiting current density is proportional to the mass transfer coefficients of the system.

Polymer electrolyte membrane fuel cells (PEMFCs) and, as well, a number of alkaline fuel cells (AFC) fed with pure hydrogen gas or hydrogen-rich fuels from renewable sources are appealing substitutes for conventional power generator devices. Pt and Pt alloy-supported on carbon are currently used in cathodes and anodes of PEMFCs. High loadings of Pt at the cathode are necessary to surmount the intrinsically sluggish kinetics of ORR. Hence, there is a necessity for increasing the Pt mass specific activity of the catalyst by lower the Pt content through alloying novel Pt efficient materials such as core-shell structure catalysts. However, in the long term substituting precious metals with non-noble metal catalysts (NNMCs) while maintaining high ORR activity and stability remains a scientific and technical goals. To achieve this goal, a number of nitrogen, metal and carbon containing catalysts were explored. It has been shown that NNMCs are material-based catalysts, implying the selection of starting precursors play significant roles in the performance of the final catalysts. Recently, additional heteroatoms such as sulfur, phosphorus and in particular boron were used for (co)doping of carbon catalysts for the oxygen reduction reaction.¹ However, all these previously reported materials showed lower ORR performances in the alkaline media than Pt/C catalysts. To achieve this goal, on one side, development of novel NNMCs using various transition metals and heteroatoms, and on the other side, improved fundamental understanding of catalytically active structural features (active sites) of these catalysts are indispensible.²
In this work, we investigated the synergic influence of metal and heteroatom on the activity of the ORR catalysts. Accordingly, we could successfully synthesized bimetallic Mn-Fe catalysts showing superior performance (activity and stability) to monometallic Fe-catalyst (state-of-the-art) and Pt/C in alkaline electrolyte. Interestingly, the activity of this catalyst in acid electrolyte is comparable to the state-of-the-art and Pt reference catalysts, while higher stability even in acid compared to Fe catalyst was observed. Additionally, the synthesis and characterization of a functionalized carbon using variable doping profiles is presented. This way nitrogen-doped and nitrogen-sulfur-, nitrogen-phosphorus-, and nitrogen-boron-co-doped carbon hybrids with a morphology containing microporous nanometer sized particles have been obtained. As-prepared heteroatom-doped carbons exhibited superior electrocatalytic activity towards oxygen reduction reaction (ORR) in alkaline and acid electrolytes. In order to investigate the active site structure and the chemical environment of the heteroatoms multitechniques were applied.
References:
[1] H.A. Gasteiger, S.S.K., B. Sompalli, F.T. Wagner, Appl. Catal. Environ., 2005. 56: p. 9.
[2] Rao, A.M., J.; Samuelsen, S. , J. Power Sources 2004. 134: p. 181-184.

The ORR (Oxygen Reduction Reaction) is an important reaction for fuel cells. Pure Pt is one of the most successful electrode catalysts for this key reaction. However, due to its expense, numerous efforts have been made to find a new catalysis system based on Pt bimetallic alloys, in which Pt is partially replaced by less expensive metals, such as Ni, Co and Fe. Experimental and theoretical works have shown that Pt₃Ni alloys have a higher ORR activity than pure Pt. Here, a cluster expansion approach based on ab-initio calculations has been used to investigate the relationship between surface structures of Pt₃Ni(111) alloy catalysts and their ORR catalytic activity. With this approach, we build a direct bridge between the atomic structure and catalytic properties of Pt-Ni alloy system at a variety of surface compositions and chemical environments. The equilibrium near-surface structures are presented as a function of O₂ partial pressure, temperature, and the chemical potentials of Ni and Pt. We discuss the relative importance of strain, ligand, and ensemble effects in determining catalytic activity, and we demonstrate how ensemble effects can be leveraged to rationally design alloy surfaces with optimal ORR activity.

The calculations of phase transitions are one of the most important topics in modern materials science particularly when it is difficult or impossible to study phase transitions experimentally, for example at high pressure. Density functional theory (DFT) has for a long time been the main workhorse of such calculations. As a simple mean-field method DFT employs different forms of approximate exchange-correlation functionals which often fail to describe accurately several phenomena such as bonding, cohesion, optical properties, conductivity and other quantum effects. As a result one can encounter over stabilization of one phase compared to another, especially if the phases belong to different classes (e.g. metal and semiconductor).
On the other hand modern Quantum Monte Carlo (QMC) methods directly solve the many-body Hamiltonian and by virtual of the variational principle are systematically improvable. Despite being more computationally demanding than standard DFT, the improved accuracy that QMC provides can justify the additional expense. In this spirit we have performed diffusion quantum Monte Carlo (DMC) calculations of the pressure-induced phase transitions of tin. In order to obtain highly accurate transition pressures we systematically assess the effects of DMC controllable approximations such as the fixed-node approximation, finite-size effects, and the use of non-local pseudopotentials. We then compare the DMC equations of state for several tin phases with DFT all-electron and pseudopotential calculations to evaluate the accuracy of exchange-correlation functionals and the choice of the effective core potential.

Polymer electrolyte membrane (PEM) water electrolysis provides the generation of hydrogen for energy storage/conversion applications with many advantages. These include the absence of corrosive electrolytes, small footprint, hydrogen generation at differential pressure, high gas purity, and the ability to operate under a wide range of power input (partial load and overload)¹. In the last years, PEM water electrolysis has received a great deal of interest. With the growing capacity of localized renewable energy sources surpassing the gigawatt range, a storage system of equal magnitude is required. When coupling renewable energy sources to water electrolysis, a carbon-free cycle can be enabled². However, the high cost of PEM electrolysis components still hinder the introduction of PEM water electrolyzers in the energy sector. Only a few materials can be selected, demanding the use of scarce and expensive materials/components such as noble catalysts (e.g. Pt, Ir and Ru), titanium based current collectors, and separator plates¹. Since the first studies on PEM electrolysis by General Electric, research groups have tried to overcome the high cost issue with innumerous alternatives. Important achievements were accomplished, but still not enough to sufficiently reduce the investment cost. In this research work, we fabricated membrane electrode assemblies for PEM water electrolysis with enhanced catalyst utilization, lower proton and mass transport resistivities, and low noble metal loadings, in order to obtain high performance cells with lower costs. This was possible by using our previous know-how on material developments made in PEM fuel cells as well addressing the physico-chemical requirements for PEM water electrolysis. Improvements could be demonstrated for membrane and catalyst configurations with up to 10 times less noble metal, and considerable cost reductions have also been proven to be achievable.
[1]. M. Carmo, D. Fritz, J. Mergel and D. Stolten, International Journal of Hydrogen Energy, 38, 4901-4934 (2013)
[2]. J. Mergel, M. Carmo and D. Fritz. Transition to Renewable Energy:Status on Technologies for Hydrogen Production by Water Electrolysis, D. Stolten, V. Scherer, Editors, p. 423-450, Wiley-VCH, Weinheim (2013)

The understanding of atomic arrangement of metal atoms in the nanoalloy catalysts is important for designing low-cost, active and robust catalysts for oxygen reduction reaction (ORR). This presentation describes findings of the investigation of the atomic structures and the electrocatalytic activities of ternary and binary nanoalloys, aiming at revealing a fundamental insight into the catalytic synergy linked to the atomic-scale structure. Examples of Pt-based ternary nanoalloys such as PtIrCo, PtNiCo, PtVCo and their binary counterparts will be discussed. The effect of thermochemical treatment temperature on the atomic-scale structure of the nanoalloys is examined as a useful probe to the structureminus;activity correlation. The structural characterization of the binary and ternary nanoalloy catalysts was performed by combining surface sensitive techniques such as XPS and 3D atomic ordering sensitive techniques such as high-energy X-ray diffraction (HE-XRD) coupled to atomic pair distribution function (PDF) analysis (HE-XRD/PDFs), as well as computer simulations. The results show that the nanoalloy&’s atomic and chemical ordering can be tuned thermochemically depending on the chemical composition, leading to enhancement in the nanoalloy&’s mass and specific activities for ORR. The results will be discussed to highlight the importance of structures of catalysts for rational design and nanoengineering of nanoalloy catalysts for electrochemical energy conversion and storage in various platforms, including flexible devices.

The catalyst particle size effect (PSE) is an essential topic in fuel cell and heterogeneous catalysis.¹ Experimental^2-4 and theoretical^4,5 studies have both shown that surface geometric and electronic structures of Pt vary with different sizes. The oxygen reduction reaction (ORR) is found to be favored on large Pt particles (>3 nm), which have a higher percentage of (111) and (100) sites.⁴ Small Pt particles (<3 nm) can be more irreversibly oxidized and the adsorbed OH group hinders the adsorption of O₂ and the splitting of O-O bond.³ Therefore, careful control of the Pt size and distribution is crucial in achieving good PEMFC performance.
In this study, Pt supported on carbon is synthesized through reactive spray deposition technology (RSDT), and are directly coated on the glassy carbon electrodes and Nafion^® membrane. Pt nanoparticles are formed through the combustion of precursor solution and then mixed with carbon sprayed from air-assisted nozzles. RSDT is unique in the approach taken to achieve a one-step synthesis of supported catalyst and allows for real-time management of the particle size and catalyst layer (CL) composition and structure.⁶ Small Pt particle formation is favored at low precursor concentration, low air quench flow, and low oxygen flow producing a fuel-rich environment. The CL composition and porosity is controlled by the ionomer to carbon (I/C) ratio and the carbon concentration in the slurry. RSDT eliminates the multiple steps in traditional wet chemistry and energy-intensive nanopowder fabrication processes. Significant reduction of Pt content in the CL has also been achieved with less than 0.05 mg_Pt/cm² Pt loading.⁷ Herein, the influence of PSE on cathode PEMFC performance is investigated. Pt particles in the size of ~2 nm, ~5 nm and up to ~10 nm are evaluated for ORR reactions in single-cell test and rotating disk electrode. Due to the limitations of the single-cell test for PSE analysis,¹ the Pt loading, CL thickness, I/C ratio and all other test conditions are kept constant. Transmission electron microscopy is used to obtain the Pt size distribution in the pre- and post- fuel cell test. Based on the results, the ORR kinetics and activity, as well as Pt utilization and mass transport in the CL are then discussed.
References:
[1] Maillard, F.; Pronkin, S.; Savinova, E.R. Size effects in electrocatalysis of fuel cell reactions on supported metal nanoparticles. In Fuel Cell Catalysis: A Surface Science Approach; Koper, M.T.M., Ed.; John Wiley& Sons: Hoboken, NJ, 2009; pp 507-566.
[2] Mukerjee, S.; McBreen, J. J. Electroanal. Chem. 1998, 448, 163-171.
[3] Mayrhofer, K.J.J. et al. J. Phys. Chem. B 2005, 109, 14433-14440.
[4] Shao, M.; Peles, A.; Shoemaker, K. Nano Lett. 2011,11, 3714-3719.
[5] Greeley, J. et al. Z. Phys. Chem. 2007, 21, 1209-1220.
[6] Maric, R.; Roller, R.; Neagu, R.; J. Therm. Spray Technol. 2011, 20, 696-718.
[7] Maric, R. et al. ECS Trans. 2008, 12, 59-63.

Ion conduction mechanisms and the nanostructure of ion conduction networks remain poorly understood in polymer electrolytes which are used as proton-exchange-membranes (PEM) in fuel cell applications. We use electric force microscopy techniques to study nanoscale surface-potential fluctuations produced by Brownian ion dynamics in thin films of low-hydration Nafiontrade;, the prototype PEM. Images and power spectra of the fluctuations are used to derive the local conductivity-relaxation spectrum, in order to compare with bulk behavior and hopping-conductivity models. Conductivity relaxation-times ranged from hours to milliseconds, depending on hydration and temperature, demonstrating that the observed fluctuations are produced by water-facilitated hydrogen-ion hopping within the ion-channel network. Spatial variations of the conductivity relaxation parameters are found in the lowest hydration material. Due to the small number of ions probed, non-Gaussian statistics of the fluctuations can be used to constrain ion conduction parameters and mechanisms.

From water treatment facilities to fuel cells, membrane-based separation processes are ubiquitous in nature and find widespread usage in many applied technologies. Despite significant differences over a wide range of length scales, one of the key, and common, features for optimizing a membrane&’s transport and selectivity properties is the well-specified control of molecular interactions in confined geometries. In practice, however, this is often only accomplished through detailed synthesis techniques or alternative routes towards functionalization due to the delicate interplay between membrane structural parameters and a desired membrane chemistry. Here, we outline a versatile new approach for the functionalization of membranes using ligands adsorbed to the surface of nanoparticles. Nanoparticles were functionalized a-priori by a suitable choice of encapsulating ligand and subsequently deposited at the pore entrances of pre-existing porous substrates. Depositing nanoparticles layer-by-layer using 2D films, the method lends itself naturally to an efficient and well-controlled design principle for the active layer of membranes of varying composition and thicknesses, which in turn retains the functionality of its individual components. We demonstrate how variations in the ligand terminal group can influence ionic transport by introducing some of the same charged groups as those found in advanced membrane technologies, such as carboxyl and amine groups in reverse osmosis membranes. Further functionality exploiting the ligands as binding sites is demonstrated for the introduction of sulfonate groups and a modification of the membrane charge density. We then extend these results to smaller dimensions by systematically varying the underlying pore diameter. The resulting nanoparticle-functionalized membranes have selective transport properties that compare well with other emergent membrane technologies such as carbon nanotubes, while maintaining one of the highest permeabilities for ionic-separation membranes to date. Leveraging the flexibility by which by which ligated nanoparticles can be synthesized, these results open up exciting possibilities for a number of functionalized components that have been chemically adsorbed onto the surfaces of nanoparticles, and for the first time, describe a means by which to deliver this highly controllable and scalable functionality to an all-important regime of porous substrates in order to influence transport.

The study of hydrogen sorption into noble metals is important for storage and catalysis. Electrochemical atomic layer deposition (E-ALD) was used in the present study. Palladium thin films were grown by repeated cycles of surface limited redox replacement (SLRR). Platinum thin films were deposited onto the SLRR-grown palladium using the same technique. Copper was used as the sacrificial element for both replacement reactions. Hydrogen was absorbed into the films by flowing 0.1M H₂SO₄ and stepping negative into the hydrogen evolution region. The potential was held long enough for the films to become saturated (c.a. 5 minutes) with hydrogen followed by stepping positive to desorb the hydrogen. The molar ratio of H/Pd was consistently near 0.7 and there were no significant changes in the H/Pd ratios upon deposition of platinum. This is in contrast to values of H/Pd reported for palladium-platinum alloys in the literature, where above a critical value of platinum content the ability to store hydrogen was lost. In addition the kinetics were studied by fitting the current profiles for 3ML palladium films and 3ML palladium films modified with platinum. It was found that even submonolayer coverage of platinum caused an increase by more than an order of magnitude in the rate of hydrogen desorption.

The hydrogen evolution reaction (HER) is of great importance in the field of sustainable energy. On its own, H₂ is a promising high-energy density fuel for storing renewable energy generated from intermittent sources such as solar and wind. However, it is also frequently a deleterious side-reaction; for example, it is the main competing reaction in devices that seek to reduce CO₂ to fuels such as ethanol and methanol. In both situations, it is necessary to have a fundamental understanding of the chemical interactions at the electrode/electrolyte interface so that catalytic activity can be enhanced or minimized, accordingly. While much research has been devoted to engineering electrode surfaces to maximize HER activity, little attention has been given to the nature of the proton-donating electrolyte in solution. Herein, we demonstrate that HER activity on Au is dependent on both the concentration and chemical nature of the proton donor. These insights can be used to tailor the choice of electrolyte to the application in order to optimize electricity-to-fuels device performance.

Cerium oxides are unique in the class of metal oxides as they exhibit interesting physico-chemical properties that enable them to be used in technological applications. The pronounced catalytic effect observed with this class of oxides led to its application in automobile exhaust, solid oxide fuel cells, optical diplays, production of hydrogen and microelectronic devices where refractive index is important. As cerium belongs to the class of lanthanides exhibiting variable electronic structure with the 4f level having the same energy as that of the 6s valence electrons. As a result it enjoys a dual valence states that affords unique redox behaviors. The transition from valence state of three to four which is a consequence of removal of 4f electron results in the ionic radius change from 1.01A^o to 0.87 A^o. Cerium oxide exists in two stable compositions; cerium sesquioxide (Ce₂O₃) and cerium dioxide (CeO₂). The crystallographic structures of the two oxides have been well analyzed. The sesquioxide is having a pseudocubic lattice type with lattice parameters (a=3.8905 A^o, c=6.0589 A^o ). It contains a sandwich of penta layers and a close packing of these penta lyers forms Type-A structure with a stable (001) surface. The sesquioxide-C type differs from Type-A in that it has 32 metal ions and 48 oxygen ions which may be considered as a fusion of eight unit cells of cubic cerium dioxide with two oxygen vacancies. The type-C sesquioxide has also been considered as a sandwich trilayer. Based on this structure, one would expect that the Type-C to have an oxidation potential lower than Type-A based on the metal ions involved in the two cases. The synthesis, and interconversion of sesquioxide has been achieved electrochemically and it shows a redox peak at 0.72 V that will be presented with Its suitability for fuel cell application and catalysis (1,2).
1. R. Press, K.S.V. Santhanam, M. Miri, A. Bailey and G. Takacs, Introduction to Hydrogen Technology, Wiley, NJ (2009) 2 .K. Deshmukh and K.S.V. Santhanam, J. Power Sources, 159(2), 1084 (2006)

We report our progress in utilizing an in situ Surface Enhanced Raman Spectroscopy (SERS) technique to better understand the active species on Pt during the hydrogen oxidation reaction. At present, it is unclear why the hydrogen oxidation reaction is more sluggish in alkaline fuel cells and electrolyzers than in acid [1]. In this presentation, we focus on elucidating the mechanism of the hydrogen oxidation reaction with a goal to understand why the hydrogen oxidation kinetics is pH-dependent. Our approach is based on SERS, which has recently been highlighted as a promising technique to investigate the oxygen evolution reaction intermediates [2]. Inspired by these results, we have created an in situ SERS setup, using Au as a platform for a catalyst support to boost the Raman cross section. By examining the Raman spectra as function of potential, we can obtain chemical information on the Pt surface during the hydrogen electrochemical reaction. We will use these results to answer the question of what chemical species are formed during the hydrogen electrochemical reaction on Pt. Influence of pH of chemical species on the electrode/electrolyte interface will be discussed, along with how to broadly apply our approach to other electrochemical systems.
REFERENCE
1. W. Sheng, H.A. Gasteiger, Y. Shao-Horn, J. Electrochem. Soc. 157 11, B1529-B1536 (2010).
2. O. Diaz-Morales, F. Calle-Vallejo, C. Munck, M. T. M. Koper,Chem. Sci.4, 2334-2343 (2013); B.S. Yeo, S. L. Klaus, P. N. Ross, R. A. Mathies, A. T. Bell, ChemPhysChem 11, 1854-1857 (2010)

The development of sustainable energy is one of the most important scientific challenges in the 21st century. A critical element for sustainable energy implementation is to have efficient energy conversion and storage. Oxygen electrocatalysis is central to enable photoelectrochemical and electrolytic water-splitting, fuel cells, and metal-air batteries. Probing a fundamental catalyst “design” principle” that links surface structure and chemistry to the catalytic activity can guide the search for highly active catalysts that are cost effective and abundant in nature. While such a design concept exists for metal catalysts, little is known about the design principles for oxygen electrocatalysis on oxides. Recent advances in identifying the design principles and activity descriptors of transition metal oxides will be presented. We will show that these fundamental concepts can be used to tune transition metal oxide surfaces with much enhanced catalytic activities. Moreover, we will discuss how oxide bulk electronic structures can influence the catalytic activities of oxides, from which two different reaction mechanisms are proposed. Lastly, connecting bulk to surface electronic structures is challenging but much needed to provide mechanistic insights, and some in-situ synchrotron X-ray measurements to this end will be discussed.

Significant efforts have focused on replacing noble metal cathodes with transition metal oxides (TMOs) in alkaline fuel cells (AFCs). Rich in compositional variety, these oxides offer surface stability in an alkaline environment, multi-valent transition metal sites essential for electron transfer to O₂, and the low cost essential for widespread implementation. Recent studies using rotating disk electrodes (RDEs) have linked compositional changes in these oxides to trends in the d-band population and position, which act as good descriptors of the catalytic efficacy. However, these electrochemical measurements rely on polycrystalline particles/films that convolute all compositional and structural changes into a bulk activity. In many cases, for instance, it is unknown whether doping a transition metal site with another metal influences the activity due to ligand or strain effects. In addition, the use of carbon as a conductive conduit between oxide particles can further complicate studies due to the carbon&’s own catalytic activity. To systematically probe the influence of strain on these oxides, we have epitaxially deposited perovskite films, including SrRuO₃ and LaNiO₃, using pulsed laser epitaxy (PLE) on lattice-mismatched substrates (e.g. LaAlO₃, SrTiO₃, DyScO₃). The resultant strained films are characterized for catalytic activity toward the oxygen reduction reaction (ORR) through a modified RDE setup that encompasses both the film/substrate and does not rely on carbon additives to enhance the conductivity. While strain is known to have large effects on the ORR catalytic activity of oxides in higher temperature environments, including SOFCs, we will present, using strained SrRuO₃ and LaNiO₃ thin films, that it can affect the room-temperature activity in potential AFC cathodes.
The work was supported by the U.S. Department of Energy, Basic Energy Sciences, Materials Sciences and Engineering Division and by the LDRD Program of ORNL.

Oxygen reduction reaction (ORR) has been extensively studied due to its important role in energy conversion systems such as fuel cells and metal air batteries. Suntivich et al. reported that perovskite oxides could be optimized for ORR catalysis from molecular orbital principles. An M-shaped relationship between activity and the d-electron number per B cation was found. At the same time, a volcano shape plot is exhibited between the activity of oxides and the e_g-filling of B ions, having a value of 1 for maximum activity.
Due to ohmic loses and low catalyst utilization of catalytic layers prepared from perovskite materials, an addition of carbon powders to the electrode becomes necessary. It has been proved that ORR in alkaline media can be catalysed by carbon materials, thus raising the question about separation of contributions of the two components in these composite electrodes. Investigations on the role of carbon materials in composite oxide/carbon electrodes, are scarce. Such an approach would allow decoupling effects of the carbon material on reducing O₂ to H₂O₂ to the unknown reaction mechanism on metal oxides particles.
In this work, the kinetics for ORR is investigated for a family of Lanthanum based perovskites dispersed at mesoporous carbon layers. Phase pure LaMnO_3+δ, LaCoO₃, LaNiO₃, LaFeO₃ and La₂NiO₄ materials were synthesised by a novel ionic liquid route. This versatile approach allows the synthesis of complex oxides with fine control over phase, morphology and composition. Oxygen reduction kinetics was probed using a rotating ring-disk electrode. Activity towards the oxygen reduction reaction was compared with commercial 20% wt. Pt/Etek catalyst. We provide conclusive evidence that the contribution of the carbon layer to oxygen reduction cannot be neglected. Using the Damjanovic&’s model, the rate constants for ORR to either H₂O or H₂O₂ were calculated for the different perovskite catalysts and rationalised according to d-electron filling of B-cations.
LaMnO_3+δ diffusion-limiting current was consistent with the 4 e^- limiting current for O₂ reduction to water on platinum single crystal and polycrystalline reported in the literature. On the contrary, Vulcan activity can&’t be neglected in the case of LaCoO₃, LaFeO₃, LaNiO₃ and La₂NiO₄ electrodes. For these electrodes, current is almost double at both kinetic and mixed regions; but the onset potential for ORR is not modified with respect to the Vulcan electrode. For LaMnO_3+δ, LaCoO₃, La₂NiO₄, and LaNiO₃ all of which present an e_g = 1configuration, the ratio of rate constants for the direct and indirect pathway decreases as the d-electron occupancy of the B-site increases. LaFeO₃ which has an e_g occupancy of 2, presents lower activity than the other oxides, being the ORR reaction mainly through the formation of H₂O₂. We expect our findings to be broadly relevant to understanding and design of transition metal oxide based catalysts for ORR in alkaline media.

The characterization of oxide catalysts is often limited by the heterogeneity of exposed surfaces and the composite nature of electrodes within fuel cells.¹ Epitaxial thin films can provide well-defined surfaces of known orientation, for which the conductivity, roughness and cation distribution can be quantitatively characterized.² We have fabricated (001) epitaxial films of La_(1-x)Sr_xMnO₃ on Nb-doped SrTiO₃ and investigated the relationship between Mn valence and catalytic activity for the oxygen reduction reaction (ORR) in an alkaline environment. The activity is maximum for an intermediate composition containing mixed Mn^3+/4+; electrochemical measurements using the facile redox couple [Fe(CN)₆]^3-/4- suggest that this trend correlates with the ability to exchange charge, determined by the electronic structure of the film surface. These results illustrate the charge-transfer dependence of the ORR mechanism and the importance of stabilizing mixed Mn valence in the catalysis of oxygen reduction.
References:
[1] J. Suntivich, H. A. Gasteiger, N. Yabuuchi, and Y. Shao-Horn, J. Electrochem. Soc. 157, B1263 (2010).
[2] K.A, Stoerzinger, M. Risch, J. Suntivich, W.M. Lü, J. Zhou, M. Biegalski, H. Christen, A. Ariando, T. Venkatesan and Y. Shao-Horn, Energy & Environmental Science 6, 1582 (2013).

The development of electrocatalysts for oxygen reduction reaction (ORR) has continued to attract a great deal of research attentions. Under acidic condition, platinum -containing nanostructures are still essential in the design of highly active and stable catalysts. Now the reported ORR area specific activity based on Pt alloy nanostructures can be over an order of magnitude higher than the typical Pt catalysts. The high catalytic activity is often directly related to the carefully design of nanostructures in Pt alloys. In this talk, I will present the new approaches developed in recent years for the preparation of Pt metal and its alloy nanoparticles with well-defined structures intended for catalyzing the ORR. Some of the representative structures include core-shell nanoparticles, facet-controlled alloy nanocrystals and framework structures. The design of intended structures of ORR catalysts is based on the chemical reaction principles, better understanding of the fundamental principles of nucleation and growth with new synthetic systems and the use of in situ characterization tools.

Using both electrochemical measurement and first-principles calculation methods, we studied the possible mechanism of transition metal-nitrogen containing carbon supported catalysts (denoted as TM-N/C) for oxygen reduction reaction (ORR) which occurs at the cathode of a polymer electrolyte fuel cell. Here, we employed the rotating ring-disk electrode voltammetry to quantify the activity of TM-N/C for ORR relative to that of precious Pt catalysts. Moreover, we employed the density functional theory (DFT) method to explore the molecular/electronic level understanding of the mechanism for ORR on our assumed TM-N/C (TM=Fe, Co) active sites. Specifically, we studied the ORR activity of both heat-treated and un-treated TM-phthalocyanines on carbon supports and assumed TM-N₄ clusters embedded in carbon graphene to be the ORR active sites. Our electrochemical measurement results indicated that the synthesized TM-N/C exhibited good activity to reduce O₂ to form H₂O (4e- ORR) on Fe-N/C or H₂O₂ (2e- ORR) on Co-N/C catalysts. Moreover, the DFT was used to study the adsorption process of ORR species O₂, O, OH, OOH, HOOH, and H₂O on candidate TM-N₄ centers. We found transition metal facilitated adsorption of ORR species which clearly demonstrates metal centered activity of TM-N/C electrocatalysts. In the TM-N/C electrocatalysts, ORR was predicted to proceed via associative mechanism and the pathway of ORR is dictated by the interaction of HOOH with candidate active site centers. Importantly, our computations show that peripheral ligands could modulate the binding strength between the ORR species and the TM-N₄ complexes. Consequently, our results suggest a catalyst with optimal performance can be developed by tuning ligands that gives delicate balance between the adsorption of ORR species O₂ and OH. Thus the catalytic activity of TM-N/C electrocatalyst for ORR is determined by the local chemical environment of active sites. Furthermore, we identified that the ORR activity of the TM-N4 clusters could be gauged by an electronic descriptor related to the d-electron orbitals of the central TM atom.

Cobalt sulfides are promising terrestrially abundant catalysts for the oxygen reduction reaction (ORR), the efficiency-limiting reaction in low-temperature fuel cells. However, the systematic development of these catalysts has been hampered by the inability to synthesize morphologically well-defined thin films on inert electrode substrates. We report a facile room-temperature layer-by-layer electrodeposition method for preparing thin crystalline cobalt sulfide catalyst films that are active for the oxygen reduction reaction (ORR) in acidic aqueous electrolytes. Optimal catalytic activities are observed for films prepared from 3 deposition cycles, and the catalysts display high tolerance to methanol and modest selectivity for the four-electron reduction of O₂ to H₂O. The preparation method allows for incremental tuning of surface composition and the unambiguous comparison of catalyst-specific activities, paving the way toward systematic optimization of this important class of oxygen reduction catalysts.

The oxygen reduction reaction (ORR) is the main cathode reaction in the fuel cell system as well as metal-air batteries. However, the ORR is intrinsically slow in kinetics due mainly to the strong O=O bond. Electrocatalysts are therefore required to lower the reaction barrier and accelerate the reaction. Platinum-based catalysts dominate the commercial market nowadays. Considering the high price of platinum and its limited quantity, we are trying to develop a nitrogen-doped, carbon nanotube based catalyst because of the much lower price of carbon and the extra benefits provided by carbon nanotubes. First, in order to enhance the mass transport involved in the ORR, we designed and successfully synthesized a 3D marshmallow-like structure composed entirely of carbon nanotubes. This unique structure would improve the reaction kinetics by offering an easier access for oxygen to the reaction site and helping in creating more catalytically active reaction sites. The significant improvement on catalytic activity was shown after doping the structure with nitrogen. Different doping methods, post doping and in situ doping, were employed to achieve better catalytic performance on ORR as well as to find the optimum nitrogen concentration and its chemical state in the final product. By comparing their catalytic activity with rotating disk electrode (RDE) measurement results, we found that polyaniline-doped sample had the best performance even better than commercial platinum-based catalysts. In addition, for the long-term stability test (in both 0.5M H₂SO₄ and 0.1M KOH), our polyaniline-doped CNT marshmallow was at least comparable to the commercial platinum-based catalyst. In order to reveal and explain the high performance of our catalyst, different characterization methods were used and a variety of 3D CNT-based catalyst were synthesized. With the help of x-ray photoelectron spectroscopy (XPS), the nitrogen and carbon content as well as their respective chemical states were revealed. By combining the RDE result and the XPS result, we found that the density of active reaction site was related to the total concentration of nitrogen, and the pyridinic nitrogen was the key factor in improving the catalytic activity. Transition metals, like iron, play a negligible role in ORR but they were found to be helpful in forming the pyridinic nitrogen in the doping process. The success of synthesizing 3D N-doped carbon nanotube marshmallow for high-performance oxygen reduction electrocatalysts is of great promise and significance in developing cheap, precious metal free catalysts to replace platinum-based electrocatalysts.

Polymer electrolyte membrane fuel cells (PEMFCs) will play a crucial role in the hydrogen economy. Non-precious, Pt-free catalysts for the electrochemical oxygen reduction reaction (ORR) in PEMFCs have been the subject of intense research. One of the most popular materials in this field are pyrolysed mixtures of Fe/C/N-containing precursors, subjected to various heating, acid washing, and milling procedures. The mechanism for the ORR in these catalysts is not well understood, and is still debated. There are two main camps; those who see Fe as part of the catalytic center; and those who see Fe as a generator of active sites, with nitrogen playing the active role in the ORR.
Resolution of this debate is hampered by the complicated chemical structure in these materials; the possible combinations of Fe, N, and C atoms that could activate ORR are many. Therefore our approach is to simplify the system by removing Fe from the equation, and clarifying the fundamental catalytic activity of nitrogen-doped carbons.
Nitrogen-doped graphene foam (GF_N) was synthesized by combustion of nitrogen-containing sodium alkoxide, followed by washing, 1000#730;C heat treatment in N₂ and H₂, and graphitization at 1400#730;C.This is a 3D carbon with micron-scale pores encapsulated by thin defective graphene walls with a thickness of around 2 nm; a surface area of > 700 m²/g; and a nitrogen content of around 0.5 at.%. The material was confirmed to be Fe-free by ICP analysis.
Linear sweep voltammograms (LSVs) of GF_N in acid show relatively high current density and mass activity for such an entrirely metal free catalyst. The onset potential (at -10 µA/cm²) is around 0.85 V, similar to many Fe-containing catalysts. The electron transfer number is 3.6, incdicating majority 4-electron transfer. We conclude that Fe-free active sites may contribute significantly to the 4-electron ORR in Fe/C/N-based catalysts (although this does not mean that Fe-centers do not also have activity).
Alkaline anion exchange membrane fuel cells (AEMFCs) have some advantages PEMFCs. For examples, the cathode reactions are much faster and more efficient in alkaline conditions, and therefore non-precious catalysts have good activity. Therefore we also applied our GF_N catalyst in alkaline. There are few rigorous durability studies published in alkaline media, therefore we propose a modified load potential cycling test, between -0.4 V and 0 V.
We show in LSVs that GF_N has comparable activity to platinum-decorated carbon black (Pt/CB). More significantly, we perform durability tests over 60000 potential cycles. We report mass activity retention of just 20% in Pt/CB. However, GF_N retains a remarkable 64% of its initial activity over the same number of cycles. This clearly demonstrates that GF_N electrocatalysts have sufficient activity and durability to be used in commercial AEMFCs for long periods of time.

Fuel cells and electrolyzers systems hold significant promise in addressing our current energy and environmental problems, as they can be used to either generate clean electricity or store it, according to our needs [1]. One can then envisage an ideal society in which electricity is produced mostly through solar, wind and nuclear energy, hence with no CO₂ emissions, stored as a fuel with an electrolyzer cell, and then used, when needed, in a fuel cell to power (and heat) our homes, cars, etc [2].
A key hurdle to this vision is the high cost of these devices, which, in turn, is linked to the materials used in them. Indeed, in order to make this technology commercially viable, we need to find new material solutions that are cheaper, environmentally friendly, abundant and that have higher performance. This poses a tremendous challenge that can only be addressed with a paradigm-shift approach to materials science, in which previous trial-and-error approaches are substituted by the rational design of materials. To this end, computer modeling is one of the most promising tools at our disposal.
In this presentation I will review some of my recent research pairing computation and experimentation, in an attempt to rationally design these materials. I will provide three examples; first I will talk about the oxide-ion conductivity in electrolyte materials and show the key role that defect interaction plays on this property [3-5]. Second, I will talk about chemical expansion in fluorite and perovskite-based oxides and how we understood the atomistic causes of this phenomenon and predicted materials with reduced expansion [6-8]. Finally I will present our latest work on the role of dislocations on the defect chemistry and oxide-ion mobility in SrTiO₃, showing that dislocations can indeed facilitate the reduction of this material and also affect its oxide-ion conductivity [9]. The work I will describe in this invited talk has been made in collaboration with researchers in ref [3-9].
[1] Wachsman et al., Science334, 935 (2011)
[2] Wachsman et al., Energy and Environmental Science5, 5498 (2012)
[3] Marrocchelli et al., Chemistry of Materials 23, 1365 (2011)
[4] Burbano et al., Chemistry of Materials 24, 222 (2012)
[5] Burbano et al., PCCP 16, 8320 (2014)
[6] Marrocchelli et al., Advanced Functional Materials 22, 1958 (2012)
[7] Bishop et al., Energy and Environmental Science 6, 1142 (2013)
[8] Marrocchelli et al., PCCP 14, 12070 (2014)
[9] Marrocchelli et al., (in preparation)

The desirable mixed ionic and electronic conductivity in many perovskite oxides are fundamentally controlled by the oxygen non-stoichiometry at equilibrium. A common practice to enhance the oxygen non-stoichiometry concentration δ in La_xSr_1-xCo_yFe_1-yO_3-δ (LSCF) is through incorporating a large amount of Sr dopants. However, the resulting metastable perovskite phases may undergo phase separation, and consequentially affect the overall device performance. In this work, we first implement our recently developed first-principles free-energy functional to predict the oxygen non-stoichiometry concentrations as a function of temperature and oxygen partial pressure. The instability phase diagram of Sr segregation on LSCF surfaces is then computed at the obtained equilibrium oxygen non-stoichiometry concentration for the bulk and surface LSCF phases, with and without the presence of CO₂. Our results indicate that when CO₂ is absent, the bulk LSCF phase is stable at all the experimentally relevant conditions, from 300 K to 1200 K and the oxygen partial pressure from 1 atm to 10^-4 atm. However, the surface LSCF phase is stable only at a small temperature and oxygen partial pressure window, between 500 K and 900 K and the oxygen partial pressure is less than 3×10^-4 atm. At the atmospheric CO₂ concentration, both the bulk and surface LSCF undergo phase separation. These first-principles computational results will be used to guide our on-going experimental efforts towards the optimal cathode materials and structure designs for the solid oxide fuel cell applications.

ABO₃ perovskite oxides are the major class of oxide materials for intermediate temperature (500 - 750 °C) solid oxide fuel cell (SOFC) cathodes, where the oxygen reduction reaction (ORR) occurs. One of the major issues that limits applications of many perovskite cathode materials is associated with perovskite surface stability and dopant segregation/redistribution near the surfaces, which strongly influences the time-evolving ORR activity under SOFC conditions. A few strategies have been recently developed to improve surface activity and stability of perovskites for SOFC cathode applications, such as surface decoration, although it is still unclear what are the fundamental origins leading to the observed activity and stability enhancement. In this work, I will discuss on the results of the ab initio based perovskite (La,Sr)(Co,Fe)O₃ (LSCF₁₁₃) and (La,Sr)CoO₃ (LSC₁₁₃) (001) surface stability analysis relevant to the SOFC conditions. Multiple (001) surface configurations, including the (001) AO and BO₂ terminations with varying surface layer Sr/La and Co/Fe concentrations, are investigated to determine the stable (001) surface composition within the stable perovskite bulk phase region relative to the lower order oxide compounds. The predicted stable (001) surface compositions within the perovskite phase are found to be (001) AO with high Sr concentration for both LSCF₁₁₃ and LSC₁₁₃, which results are in good agreement with experimental observations In addition, the ab initio surface stability analysis predicts that LSCF₁₁₃ has saturated surface A-site Sr content, while for the stable LSC₁₁₃ (001) surfaces the A-site Sr occupation is only partial. The ab initio LSCF₁₁₃ and LSC₁₁₃ surface stability analysis results are further used as a foundation for understanding the distinct ORR activity enhancement between LSCF₁₁₃ and LSC₁₁₃ with surface LSC₂₁₄ decoration (relative to the undecorated LSCF₁₁₃ and LSC₁₁₃). By incorporating the calculated thermodynamic driving force of Sr substitution (with La) in bulk LSCF₁₁₃ and LSC₁₁₃ relative to the (La,Sr)₂CoO₄ (LSC₂₁₄), we discuss possible origins for the distinct ORR activity enhancement (relative to the undecorated material) between LSCF₁₁₃ and LSC₁₁₃ with surface LSC₂₁₄ decoration.

Enhancement of ionic conductivity in thin films or multilayers of oxide materials, i.e. doped zirconia and ceria, has sparked great interest in the search for fast ion conducting structures for fuel cells. The enhancement in ionic conductivity in such structures could be attributed to elastic strain arising from the lattice mismatch at the interface. However, this assumes that the interface between two materials is perfectly coherent, while in most cases dislocations are observed, which relax the interfacial elastic strain. The strain field and the electrostatic field that arises from the dislocations can also impact the defect stability, distribution and mobility in these materials; and yet, the role of dislocation on the ionic conductivity is not consistently reported in the literature nor is it clearly understood.
In an attempt to shed light on this issue, an 1/2<110>{100} edge dislocation in reduced or doped ceria (doped with gadolinia, yttria and scandia) is chosen as a simulation. Redistribution of dopant cations and oxygen vacancies is found upon after relaxation. As a result of elastic energy minimization#65292;dopants larger than host cations enrich at the tensile strain zone around the dislocation while a depletion zone of dopant cations is equilibrated on the compressive strain region around the dislocation. The oxygen vacancies follow the same trend of dopants redistribution due to the electro-static interaction between the dopant cations and the oxygen vacancies. As opposed to the speculations that regard dislocations as fast diffusion paths as those in metal, the edge dislocation was actually found to impede oxygen transport in these doped and reducible oxides. Since the ionic conductivity in ceria has a non-linear dependence on the dopant concentration, with a maximum at 8-10 % concentration of dopants, both the enrichment (>20%) and depletion zones (<5%) of dopant cations around the dislocation impede oxygen transport and reduce the local ionic conductivity. Moreover, our hypothetical model, where no dopant cation exists, shows that the redistribution of oxygen vacancies around the dislocations leads to a strong vacancy-vacancy interaction which also slows down the oxygen transport.
Our work demonstrates that dislocations can be detrimental to oxide ion transport by the accumulation of charged defects in doped or reducible oxide materials, where oxygen transport is mediated by oxygen vacancies. Therefore, their effect must be considered in quantitatively interpreting the experimental results aiming to assess the effects of strain in oxide ion conductivity.

In the recent years, heterointerface engineering has drawn a significant focus as a design parameter to enhance oxygen transport. Both experiments and simulations have satisfactorily shown that tensile strain lowers oxygen migration barriers, thus, providing a degree of control over defect kinetics. However, similar effects of strain on thermodynamic stability of oxygen vacancies have not been fully understood. In this work, we investigate the effect of strain on the stability of oxygen vacancies in interface structures, such as between CeO₂, ZrO₂ and ThO₂, as well as SrTiO₃ and MgO. We show that interfacial strain can be used to preferentially stabilize oxygen vacancies, i.e., vacancies can be stabilized at the interface, or inside either of the adjacent materials, thus providing control over their location and concentration. Based on this thermodynamics and kinetics analysis, we show that in order to design high ion conducting layered materials, the choice of materials requires striking a balance between the strain-dependent formation and migration energy of oxygen vacancies.
In this work, we will also discuss the concept of chemical expansion of charged and neutral vacancies, and elucidate that while the neutral vacancies lead to lattice expansion, the charged vacancies lead to contraction. Thus, the neutral and charged vacancies are expected to stabilize under tensile and compressed strains, respectively.
This work was supported by U.S. DOE, BES, MSED.

Computational techniques based on first principles methods are an indispensable component of Materials Genome Initiative to accelerate the research and development of new materials. In this talk, I will present our study of developing first principles techniques to design novel oxygen solid-state electrolyte materials. Using the recently identified Na0.5Bi0.5TiO3 perovskite oxygen ionic conductor as an example, we determined a various properties of interests for this new solid electrolyte using first principles calculations. I will demonstrate the computational design of Na0.5Bi0.5TiO3 that achieves good stability and an order of magnitude increase in ionic conductivity.

This study investigates surface segregation and phase formation behavior in La_xSr_1-xCo_0.2Fe_0.8O_3-δ (LSCF), a widely used cathode material for solid oxide fuel cells (SOFCs). (100)-oriented LSCF thin films with varying ‘x&’ values were deposited on (110)-oriented NdGaO₃ (NGO) substrates by pulsed laser deposition (PLD). Compositional changes on the surface of LSCF thin films were measured using synchrotron based total reflection x-ray fluorescence (TXRF) technique in real time at 800°C under different CO₂ partial pressures. Ex-situ electronic structure measurements were carried out on the post-annealed samples using synchrotron based hard x-ray photoelectron spectroscopy (HAXPES). The morphological changes at the surface have been examined by AFM studies. The thin films were also characterized in cross-section by high-resolution transmission electron microscopy (HRTEM), and composition profiles in the LSCF matrix adjacent to the surface segregated phases were analyzed using energy-dispersive x-ray spectroscopy (EDS). The thermodynamics and kinetics of this segregation phenomenon will be discussed in light of first-principles computational calculations.

The perovskite catalysts La_0.75Sr_0.25Cr_0.5X_0.5O_3-δ (where X= Mn, Fe and Co) were prepared by combustion synthesis and the influence of the substitution on the catalytic activity and selectivity of the catalysts in steam reforming of both pure and by-product glycerol to produce hydrogen for the utilization of solid oxide fuel cell was investigated. All the catalyst systems were found very active and selective with Fe-substituted catalyst slightly more active. Hydrogen yield and coke suppression was better in Mn-substituted catalyst and also structurally more stable in fuel environment. Impregnation of Ni into the lattice structure of the catalysts and subsequent redox exsolution of Ni nano particles supported on the oxide surface of the materials has significantly improved the hydrogen yield and proved more effective than the traditional wet impregnation of nickel nanoparticles on the surface of a support. The extent of the exsolution phenomenon observed in the materials followed the order LSCM > LSCC > LSCF.

Pure, dry hydrogen required for power in fuel cells and industrial applications may be produced efficiently by steam electrolysis employing a ceramic proton-conducting membrane in a high temperature range, 600 - 900 °C [1]. Nonetheless, the study of Protonic Ceramic Electrolyser Cells (PCECs) is still in its infancy, and mapping of transport properties under a range of conditions relevant to electrolysis is important for further development of these promising devices. Ionic and electronic transport numbers are usually determined by the use of concentration cells, in which a chemical potential gradient created by a partial-pressure difference of active gaseous species such as H₂, O₂ and H₂O, produces a measurable electrical voltage [2]. In the classical methodology, the measured electromotive force (emf) is directly related to the transport properties. However, under real conditions the presence of polarizable electrodes may produce misinterpretation of the ionic and electronic transport properties. In this work, we examine the emf method for ionic and electronic transport number determination of the material Sr_0.9Y_0.1ZrO_3-δ + 4% ZnO in detail, extending our previous study [3] to reducing conditions. The methodology is modified by the introduction of the electrode polarization effect and a parallel variable resistance. Appropriate equivalent circuits are adopted and the effect produced by the external resistance on the measurable emf is demonstrated to be suitable for accurate determination of transport numbers under variable conditions. The modified methodology is implemented for determination of the electrical properties of a dense ceramic membrane in a dual-chamber cell equipped with a YSZ pO₂ sensor. The gas compositions in the two chambers are controlled by a series of mass-flow controllers for simultaneous control of pO₂, pH₂ and pH₂O. It is experimentally confirmed that accurate determination of transport numbers requires the modified methodology, especially in the case of poor reaction kinetics at the electrodes.
1. T. Sakai, S. Matsushita, H. Matsumoto, S. Okada, S. Hashimoto, T. Ishihara, Int. J. Hydr. Energy 34 (2009) 56-63.
2. D.P. Sutija, T. Norby, P. Björnbom, Solid State Ionics 77 (1995) 167-174.
3. D. Pérez-Coll, G. Heras-Juaristi, D.P. Fagg, G.C. Mather, J. Power Sources 245 (2014) 445-455

Ionic conducting metal oxide thin films for miniaturized Si-devices such as fuel cells and electrolysers are of high relevance to allow for quicker response times, and higher energy conversion efficiencies. Recently there is strong evidence in literature that metal oxide thin films such as doped ceria or zirconia show a strong dependency of oxygen ion conduction on lattice strain due to electro-chemo-mechanic interaction (1,2). In this paper we review recent advances in this field and discuss different levels of strain-oxygen ionic transport interaction for micro-Solid Oxide Fuel Cell electrolytes. The first part focuses on the role of strained interfaces on near order and ionic transport for Er₂O₃/Ce_0.9M_0.1O_1.9-x heteroostructure thin films and dots grown on sapphire (3). The material system Gd_0.1Ce_0.9O_2-x/Er₂O₃ was investigated by changing the number of interfaces from 1 to 60 while keeping the device at a constant thickness (3). Electrical measurements showed that the activation energy of the devices could be altered by Δ0.31 eV by changing the compressive strain of a micro-dot ceria-phase by 1.16%. The near-order ionic transport interaction is supported by Raman spectroscopy measurements, which are introduced as new measurement technique to investigate and describe the strain state with high spatial resolution. For this, a novel microfabrication strategy was developed and applied in order to sandwich strained heterostructure dots between two electrodes on microfabricated chips. Secondly, we connect supported and free-standing Gd_0.2Ce_0.8O_1.9-x membranes to micropatterned top Pt micro-electrodes and study directly the impact of compressive strain patterns to locally resolve ionic transport (4). Substrate supported films reveal an activation energy of 0.77 eV for zero-strain. Comparison to the free-standing membranes with same electrode geometry show that a local compressive strain results in an increase of the ionic conductivity activation energy by +0.16 eV for 0.46% of local strain (stress of ~1.1 GPa) between the electrodes. We report a measurable impact of strain on ionic conduction for the electrolytes and confirm that compressive local strain affects the activation energy of ionic transport. The effective strain of the oxide membrane depends on the electrode area design and the acting electro-chemo-mechanics.
Both examples of strain and electro-chemo-mechanic engineering based on ceria electrolytes implicate new guidelines for energy converting micro-devices such as Solid Oxide Fuel Cells in which the oxide membranes are the functional part for fuel cells.
References: (1) J.L.M. Rupp, Solid State Ionics 207, (2012) 1-12; (2) J.L.M. Rupp et al., Adv. Funct. Mat. 20, (2010) 2807-2814
(3) S. Schweiger et al., ACS Nano, 2014 8(4) (2014), pp 5032-5048; (4) Y. Shi, A.H. Bork and J.L.M. Rupp, Advanced Materials, submitted (2014)

We present here a method that utilizes extrusion-based, room temperature 3D-printing of liquid inks to create mutli-material, free-standing, robust, complex SOFC constructs including cells, interconnects, and gas channel structures. The inks are comprised of high volume fraction (0.7-0.9) particles, elastomeric binder, and graded volatility solvents. Unlike other non-elastomeric binding materials used in powder-based fabrication, the rapid precipitation of elastomer from the solvents upon extrusion results in densification of the surrounding powder, producing solid fibers that may be continuously deposited. Lower volatility solvents remain within the deposited strands and permit immediately adjacent layers and fibers to seamlessly fuse together over the course of minutes. This ultimately results in monolithic, high fidelity (sub 100 µm feature size) objects that can be physically handled immediately after printing. Inks comprised of mixed NiO+YSZ, YSZ, (La,Sr)MnO₃ (LSM), and (Sr,La)TiO₃ (SLT), respectively representing anode, electrolyte, cathode, and interconnector materials, were co-3D-printed to create simple SOFC stacks containing gas channels and interconnect features. Although we primarily focus on the function and properties of these simple stack structures, we also provide examples of how 3D-printing permits the design and fabrication non-traditional SOFC structures. The 3D printing has also been integrated with tape-cast layers; the latter comprise the SOFC functional layers, while the former provide the gas channel and interconnector structures. In order to produce entire 3D-printed stack structures, the multi-material constructs must be co-fired to yield components with the desired dense or porous structures, with intimate interfaces between layers, without significant reactions or interdiffusion between materials, and without warping or cracking. As noted above, the low volatility solvents in the printed fibers provide good bonding between printed fibers and also with tape-cast layers. Shrinkage matching is achieved through tailoring the ink composition for each component to produce equivalent shrinkage during the firing process. An Fe₃O₄ sintering aid is used in some layers to increase shrinkage, allowing all components to be co-fired at 1250^oC without interdiffusion/reactions. In particular, we have shown than entire Ni-YSZ/YSZ/LSM-YSZ cells can be co-fired at 1250^oC, low enough to avoid LSM-YSZ reactions and to yield a desirable porous LSM-YSZ cathode structure; the SOFCs yielded a power density of nearly 1 W/cm² at 800^oC. Furthermore, dense LSM/SLT bi-layer interconnectors have been fabricated at 1250^oC and shown to provide reasonable conductivity. Results will be presented on the printing and subsequent processing, the materials microstructures, and electrical and electrochemical cell testing.

Gradual internal reforming of ethanol was demonstrated in a high-current output anode- supported fuel cell. State-of-the-art single cells composed of (La,Sr)MnO₃ cathode, 8 mol% yttria-stabilized zirconia (YSZ) electrolyte, and YSZ-Ni anode were fabricated at Forschungszentrum Jülich and used for long term testing on anhydrous (direct) ethanol. A catalytic layer of gadolinia-doped ceria with 0.1 wt.% of Ir was deposited onto the surface of the YSZ-Ni anode support to promote ethanol reforming. A fixed catalyst layer thickness and porosity were attained by thermal treatment at 850 °C in inert atmosphere. The catalyst was designed for the reforming of the main compounds resulting from the thermal decomposition of ethanol, such as methane, and to inhibit the formation of ethylene, which is known as a source of carbon deposits. Single cells were operated in both hydrogen, which was necessary for the anode reduction, and direct ethanol delivering similar power output for both fuels. The single cells were kept at 0.6 V while monitoring the current drained from the cell at 850 °C for up to 650 hours. The obtained results indicate that the water released by the electrochemical oxidation of reformate hydrogen at the electrolyte/anode active interfaces is sufficient to ensure the reforming of the primary fuel in the catalytic layer. Post-test analyses of the samples revealed no evidence of carbon deposit formation in the anode. The experimental results provided compelling evidence for the viability of gradual internal reforming of ethanol in solid oxide fuel cells.

Lanthanum based pervskites are promising candidates for solid oxide fuel cell (SOFC) cathode materials due to high catalytic activity toward oxygen reduction reaction. Over the past decades, many efforts have been made to lower the operating temperature of SOFCs to enhance long term stability of the performance, reduce manufacturing cost and therefore secure commercial viability. LSCF and LSM are the most commonly used cathode materials for lower temperature SOFCs. However, both cathodes have not yet realized high performance and long term stability at the same time. LSCF shows excellent catalytic activity due to high ionic-electronic conductivity and rapid surface oxygen exchange. However, long term performance degrades due to phase instability - surface strontium segregation. On the other hand, LSM is free of Sr segregation and shows higher long term stability. However, LSM is not suitable for lower temperature SOFCs due to low catalytic activity toward oxygen reduction reaction. Recent researches discovered that LSM exchange oxygen slowly at the surface, not by low surface exchange coefficient, but by low oxygen vacancy concentration. To accept oxygen readily at the surface, large number of oxygen vacancies must be provided. It is interesting that the surface oxygen exchange of LSM is even higher than that of LSCF. Recently Professor Liu's group coated LSCF cathode with LSM by infiltration and enhanced the SOFC performance. We employed this methodology and propose a better way to enhance the performance and secure long term stability. LSCF-LSM and LSC-LSM core-shell nano powders were fabricated by co-precipitation process, and SOFC cathodes were made by mixing the core-shell powder with doped ceria. The co-precipitation process in this work took place in a continuous stirred tank reactor, which is ideal for mass production of powder. It is also possible to create a composition gradient between the core to the shell part. The core powder can be either synthesized or purchased. Also, calcination conditions for large amount of nano powders will be discussed. The same process was applicable to the anode powders, which result in ceria powder with nickel coat. This result will be also shared.

Solid oxide fuel cell (SOFC) has been successfully demonstrated to generate power in “fuel cell” mode and produce chemicals in “electrolysis” mode with high efficiency and low emission. Consideration of a SOFC for energy storage is, however, limited only to the production of H₂ from H₂O, followed by storage in a pressurized tank or solid. This is clearly not an energy efficient process for a high temperature system such as SOFC.
Recently, the presenter&’s group demonstrated a new bifunctional SOFC energy system that is capable of generating electric power, producing value-added chemicals and storing electrical energy with high efficiency and low emission. The new system is comprised of a reversible SOFC electrical charger/discharger and a redox-active chemical energy storing bed. During operation, the cathode of the system is constantly open to air while the anode configuration defines the true functionality of the system: power generation/chemicals production when the anode chamber is open to a flowing fuel or steam, and energy storage when the anode chamber is closed next to a neighboring multivalent metal/metal-oxide chemical bed.
The presentation highlights recent progress made in the present&’s group towards enhancing the performance and lowering the operating temperature of the new system. These highlights include the development of a new low-temperature, low-cost and rare-earth free electrolyte, atomic layer deposition stabilized nanostructured bifunctional cathodes and carbothermic reaction derived robust multivalent iron-based chemical bed.

An experimental setup consisting of a dilatometer (to monitor shrinkage), an impedance analyzer (to collect impedance data) and a power supply (to apply 10-70 V ac voltage at frequencies in the 500-1000 Hz) was used to produce half unitary planar single solid oxide fuel cells (zirconia-8 mol% yttria solid electrolyte films deposited on zirconia-8 mol% Y₂O₃/NiO anode). At temperatures below the conventional sintering temperatures, the co-sintering of small (5.0 x 5.0 x 1.5 mm³) anode-supported half-cells was achieved without any warping or crack formation. The application of 60 V at 1000 ^oC during 10 minutes, for example, yielded thin dense solid electrolyte on top of thick porous anode. The electrical behavior of the cells with Pt cathode was analyzed by impedance spectroscopy measurements in the 10 Hz-10 MHz range from 400 to 800 ^oC. The microstructure of both anode and electrolyte surfaces and also of the cross section of the half-cells were observed in a FEG scanning electron microscope. Besides the adequate cross section microstructure, i.e., dense electrolyte and porous anode, nickel metal was detected by EDX analysis in the intergranular region of the anode. This might be due to Joule heating, caused to the electric current pulses resulting from the application of the ac voltage, which could provide not only densification but also nickel oxide reduction. The main results consist on shrinkage curves, impedance plots and scanning electron microscopy micrographs. The electric field-assisted sintering showed the ability of simultaneously sintering electrolyte and anode as well as co-reducing the anode.

The use of nanomaterials in Solid Oxide Cells (SOC) has received special interest in the recent years since it has been proved they greatly enhance the performance. However, only few works have been devoted to study the long-term stability of the nanostructured electrodes under realistic SOFC/SOEC operating conditions although is one of the primary concerns.
Diminishing the stability issues by engineering new materials and electrode structures will help to meet the cost and performance goals. In our recent works different strategies to stabilize nanostructures as electrode materials of SOCs were presented.
On one hand stable compact nanostructured cermets are fabricated by alternatively filling the interpenetrated channels of the 3D double gyroid structure use as hard template [1].
On the other hand contrary to the widely employed high temperature stabilization inside the template, thermal stability is achieved by getting simultaneously the amorphous and crystalline phases before the removal of the template, forcing the so-called self-limited grain growth regime [2].
Here the performance and long-term stability of fully mesoporous electrodes Solid Oxide Fuel Cells are presented under realistic and severe operational conditions for more than 1000 hours. The performance and long term stability of same electrodes are also presented in Solid Oxide Electrolyzer Cell mode. The characterization of the cells after the tests demonstrate the electrodes keep their nanostructure, further confirming the recent and novel thermal stability strategies developed in previous publications [1,2]. The cell performance optimization in each mode, and the different involved mechanisms, are discussed in the present work.
[1] L. Almar, B. Colldeforns, L. Yedra, S. Estradé, F. Peiroacute;, A. Morata, T. Andreu, A. Tarancoacute;n, J. Mater. Chem. A, 1, (2013) 4531.
[2] L. Almar, T. Andreu, A. Morata, M. Torrell, L. Yedra, S. Estradé, F. Peiroacute;, A. Tarancoacute;n, J. Mater. Chem. A, 2, (2014) 3134.

The performance (i.e. oxygen exchange rate) and degradation (e.g. segregation and poisoning) of electrochemical energy conversion devices such as Solid Oxide Fuel Cells (SOFC&’s) and Solid Oxide Electrolysers (SOEC&’s) depends on the exchange of oxygen at the surface of a solid oxide electrode. However, little is known about the precise mechanisms and active sites involved in the surface exchange reaction in these devices.
Patterned microelectrodes, fabricated by Pulsed Laser Deposition (PLD) and lithographic techniques, are attractive for mechanistic studies of electrochemical reactions on solid oxide electrodes because their geometry can be well controlled. The dependence of the ASR on geometric parameters such as area, thickness and triple phase boundary length can be used to infer the oxide electrode reaction pathway(s). In addition, such electrode structures have a key benefit for surface analytical studies; the outer surface of a dense electrode, which is exposed to the analytical beam, is necessarily the electrochemically active surface.
Low Energy Ion Scattering (LEIS) spectroscopy, which can determine the elemental composition of the very outer atomic layer of a sample, is recently attracting much interest. Due to its relatively poor lateral resolution, most reported LEIS studies to date have been on “bulk” single phase ceramics. However, the very latest generation of instrumentation offers improved lateral resolution, opening the possibility of the analysis of “real” electrochemical (half-)cells, as opposed to isolated analyses of the component materials in single-phase form. Correlation of LEIS analyses of the surface composition of these cells, with electrochemical characterisation will be a powerful tool in understanding the performance and degradation of solid oxide electrochemical devices.
Analyses of the surface composition of half cells with LSCF micro-patterned electrode structures on a single crystal YSZ electrolyte has revealed some similarities with bulk studies, and some intriguing differences. Consistent with the literature, the surface of the perovskite electrode shows strong segregation of the Sr component, as well as the absence of transition metals. The electrolyte shows segregation of impurities such as Si and Ca, which has been previously reported in the literature, although it does not appear as severe in the present case.
In addition, there is evidence of some inter-diffusion of cations from one component to another; La from the electrode is detected on the electrolyte surface, whilst impurity cations (Na, Si) from the electrolyte appear to migrate to the electrode, which may account for the apparently “cleaner” electrolyte surface in this half-cell.

We describe a technique for measuring the activation energy of ion diffusion in ionic and mixed ionic/electronic conductors. The technique is based on monitoring small changes in refractive index near the interface of a semitransparent gold electrode with the sample surface. Constant bias voltage is applied to the sample to weakly perturb the distribution of charge carriers near this front electrode. The relaxation process induced by bias removal is probed by applying alternating voltage and monitoring by ellipsometry with lock-in detection the changes in the refractive index dominated by changes in material polarizability. Since the ionic contribution to the total material polarizability is much larger than that of electrons or protons, the diffusion of ions can be distinguished. Measurements were made as a function of temperature on single crystals of 8mol% Y-stabilized zirconia (YSZ8), on ceramic pellets of 20 mol% Gd doped CeO₂ (GDC20) and on single crystals of 0.03 mol% Fe-doped SrTiO₃ (Fe-STO). In YSZ8, a single moving species (oxygen vacancies) with activation energy of 0.8 eV was detected. The “wet” and “dry” states of GDC20 can be clearly distinguished: in the “wet” state there are mobile species other than oxygen vacancies, most likely protons. In Fe-doped SrTiO₃, the proposed technique can reliably measure the activation energy of oxygen ion diffusion on a background of the much larger electronic conductivity.

Alternative methods for power supply are needed to solve the energy challenge for the future. Renewable energy can be harvested from the sun, but solar power is discontinuous and depends on the geographic location. Solid oxide fuel cells (SOFCs) are devices that allow high power conversion efficiency, needed for a sustainable future of fuel saving and greenhouse gas emission reduction, but they supply power in a continuous mode when fed with the fuel and air. Though, in many applications power demand is variable over time. For both solar power and SOFCs, integration in the grid of energy storage is needed for leveling the energy supply. Solid oxide electrolysis cells (SOECs) are one promising storage technology that allows hydrogen production from steam. Hydrogen is attractive as energy carrier and as a clean fuel for a number of applications. Chemically stable high temperature proton conducting oxides are promising electrolytes for operating SOFCs at 600°C, which will push for a wider practical application than for the high temperature SOFCs, and for solving the present drawbacks of SOECs. However, for such a low temperature efficient air electrodes need to be developed to avoid polarization losses. Considering SOFCs, several good cathode materials have been developed for oxygen-ion conducting electrolytes, and in early works those same materials have been used also for proton conducting electrolytes. Though, using a proton-conducting electrolyte, protons migrate through the electrolyte from the anode to the cathode side, where they react with oxygen ions generating water. Thus, in principle a cathode material that performs well with an oxygen-ion conductor is not adequate for a proton-conducting electrolyte. This work will present the rational approaches used to tailor cathode materials with low overpotential, taking into account the different species involved in the cathode reactions for proton conducting electrolytes. The materials should concurrently possess electron, proton and oxygen-ion conductivities. In fact, the most performing cathode was made of a mixed oxygen-ion/electron conductor and a mixed proton/electron conductor composite, which allow extension of the active reaction sites to the whole cathode surface area.

The electrochemical performance of SOFC electrodes is greatly influenced by the microstructure and intrinsic material properties. The complex interplay between various transport processes (e.g. ionic and electronic transport) and electrochemical processes (e.g. fuel oxidation) depends on the corressponding transport-relevant parameters (i.e. tortuosity, constrictivity, percolation level, volume fraction) and active reaction sites (i.e. Triple phase boundary, TPB). Quantification of the relevant microstructure parameters is necessary to fully describe microstructure characteristics. Over the last years, state-of-the-art high-resolution tomographic techniques made it possible to quantitatively describe microstructure parameters and consequently, to analyze and to understand microstructure-performance relationships. However, in order to understand this mechanistically, models that simulate electrode reaction mechanism and incoporate these microstructure parameters in simulations must be developed.
In this work, a relationship between the transport-relevant parameters determined recently is used to quantitatively describe the extent of microstructure effects in effective transport properties of the electrodes (i.e. effective conductivities). Insights on the effects of microstructure degradation on the electrochemical performance are also provided. The description and analysis of the the TPB are also presented, in which changes are also correlated with loss of electrochemical performance. A model that incorporates the relevant microstructure parameters is used to simulate the complex anode reaction mechanism to evaluate the different components of the area specific resistance (i.e. ASR-transport, ASR-activation). Insights on the limitations in charge transport affecting electrochemical performance due to microstructure effects is all presented. The simulated ASRs are compared with experimental data obtained from impedance measurements (EIS). The results of this work give a deeper understanding on the complex relationship between microstructure parameters, material properties and electrode performance.

The exchange kinetics of oxygen between gas phase and solid cathode materials plays a critical role in the performance of cathodes for solid oxide fuel cells (SOFCs). The process occurs through an oxygen reduction reaction (ORR) involving a gaseous oxygen molecule (O₂) being adsorbed on the surface of the oxide that combines with 4 electrons to incorporate as two O^2- in the bulk material. In this work we use a thermo-kinetic model based on DFT-energetics to explore possible molecular mechanisms of the ORR on the (001)-AO and BO₂ surfaces of SOFC cathode material La_1-xSr_xCoO_3-δ (LSC). We make quantitative predictions of oxygen surface exchange rates of mechanisms of ORR on both AO and BO₂ surfaces of La_1-xSr_xCoO_3-δ, thereby identifying the fastest mechanisms on both surfaces. We find that the fastest ORR mechanism on BO₂ termination can be roughly 2-orders of magnitude faster than the mechanisms on AO termination. The predicted oxygen exchange rates are overall in good agreement with the experimental data for LSC for Sr-concentrations of 40% and 50%Sr and for a range of PO₂ and temperatures. Based on the findings of the combined ORR rates of AO and BO₂ terminations we propose a possible hypothesis to explain the ORR performance degradation commonly observed over tens of hours on LSC thin films. Our results elucidate the detailed atomistic mechanism of oxygen exchange on the surface of LSC and demonstrate a method to make semi-quantitative prediction of surface exchange mechanisms and rates for SOFC cathodes and other oxygen exchange materials.

Novel oxides with layered structures have attracted great interests of researchers not only for fundamental understanding of oxygen intercalation and transport phenomenon, but also for potential application as solid oxide fuel cell (SOFC) cathode material. In these layered oxides, exemplified by Ruddlesden-Popper (RP) phase A₂BO₄ and Brownmillerite (BM) phase ABO_2.5, the oxygen exchanges happens through the process of oxygen intercalation, which means oxygen is incorporated into a 2D oxygen interstitial network (RP) or 1D oxygen vacancy channel (BM). This introduces anisotropy into the oxides. Oxygen diffusivity and surface exchange have been proved to be highly anisotropic in these layered oxides. On the other hand, lattice strain effects have received significant interest recently for altering the kinetics of oxygen ion diffusion and surface reactions in functional oxides used as electrodes and electrolytes of SOFCs. However, comprehensive understanding of effect of strain on oxygen exchange via intercalation of these layered oxides still remains elusive.
We chose RP phase Nd₂NiO₄ (NNO) and BM phase SrCoO_2.5 (SCO) as model system in order to uncover the correlation between lattice strain and oxygen intercalation kinetics in layered oxides. Pulsed laser deposition was utilized to fabricate NNO and SCO thin film with both (001) orientation (intercalation channel in plane) and (100) orientation (intercalation channel out-of-plane). For each orientation, single crystal substrates with proper lattice parameters were chosen to introduce different strain states. Surface chemistry is of vital importance to determine the kinetics of oxygen exchange kinetics. In order to study the effect of strain on surface chemistry of NNO and SCO, we performed in situ ambient pressure X-ray photoelectron spectroscopy (APXPS) under experiment environments closer to realistic operation conditions for SOFC cathode. APXPS results revealed that for NNO, the strain along the (001) direction is the primary factor to determine the oxygen non-stoichiometry of the NNO oxide thin films. The NNO films with compressive strain along (001) are more reducible compared to the tensile strained films. The study on SCO is still undergoing. Investigations to directly determine and compare the oxygen exchange kinetics have been done using electrical conductivity relaxation (ECR). ECR results proved faster surface exchange for (100) samples compared to (001) samples. Moreover, tensile strain along (001) accelerated the oxygen surface exchange. In this work, the strain response of layered oxides represented by the model NNO and SCO composition was found to be anisotropic, and the strain along the (001) orientation was found to be a key parameter to alter the surface chemistry and oxygen surface exchange kinetics. This work has important meaning on better understanding how to use lattice strain to enhance the electro-catalytic activity of the layered oxides as SOFC cathodes.

Heterogeneous materials, which consist of two or more phases, share many benefits in the energy-converting devices. However, the heterogeneity may lead to the loss of chemical stability at high temperature application. The composite cathode (La_0.8Sr_0.2)_0.95MnO_3-δ/(Y₂O₃)_x(ZrO₂)_1-x (LSM/xYSZ) provides higher ionic conductivity and larger triple phase boundary area for solid oxide fuel cells (SOFCs), but it suffers from the formation of La₂Zr₂O₇ (LZO) and SrZrO₃ (SZO) during the high temperature process in the synthesis and operation, which worsens the cathodes&’ performance. Thanks to the most advanced high flux neutron source, the thermal stability of LSZ/xYSZ is determined using in-situ neutron diffraction. Our work highlights the visualization of the phase evolutions in heterogeneous material systems at high temperatures, along with the analysis of the diffusion activities of transition metal ions that reveal the reaction mechanism and kinetics. It is found that the tetragonal-to-cubic phase transition in YSZ at T > 900 °C leads to a heterogeneous redistribution of Mn ions. The subsequent reaction of LSM and YSZ occurring at T > 1100 °C is revealed as a three-stage kinetic process, yielding La₂Zr₂O₇, SrZrO₃ and MnO. The diffusion activities of Y, Mn and La ions in the heterogeneous systems at elevated temperatures are derived by the structural analysis, and the three-stage reaction of YSZ and LSM is found strongly correlated to Mn, Y and La ions&’ distribution and solid solubility in the multiple phases as functions of temperature.

Perovskite materials with mixed ionic-electronic conducting materials (MIEC) are being intensively studied for their application as Solid Oxide Fuel Cells (SOFC) cathodes and Solid Oxide Electrolyzer Cell (SOEC) anodes. However state-of-the-art materials, such as LSC or LSCF, present a number of problems under operation conditions: reactivity with the electrolyte (YSZ), differences in thermal expansion coefficient, degradation and durability issues. Although the search of new materials with improved properties is crucial, the screening of novel compositions by conventional synthesis methods is a complex and time consuming task. Alternatively, the application of a combinatorial approach to material synthesis opens a new avenue on the generation of entire compositional diagrams in a single experiment.
In this work, a novel methodology for screening materials with mixed conducting properties is presented. The methodology is based on a combinatorial deposition of thin films by Pulsed Laser Deposition (PLD) on 4-inch silicon wafers. This technique allows generating full range binary and ternary diagrams of compositions even for very complex oxides (due to an excellent transfer of the stoichiometry). The structural and compositional properties of the films were mapped by XRD and EDX, while Isotope Exchange Depth Profiling combined with Secondary Ion Mass Spectroscopy (IEDP-SIMS) was carried out for evaluating the oxygen exchange and ionic transport properties. As a proof-of-concept, a binary diagram of La_0.8Sr_0.2Mn_xCo_1-xO_3±δ covering the whole range of compositions from x=0 to x=1 was fabricated. After an accurate analysis of the map of compositions generated by combinatorial PLD, we successfully obtained spatially-resolved oxygen mass transport properties (self-diffusion and surface exchange coefficients, D* and k*, respectively) between 6000C and 8000C. The enhanced D* values obtained (in comparison to the bulk compositions) revealed the important role of the grain boundaries in the oxygen diffusion properties of these columnar nanostructured La_0.8Sr_0.2Mn_xCo_1-xO_3±δ films.
This original study validates this methodology as an extremely powerful tool for addressing the search of new materials for SOFCs and SOECs and opens the possibility of tuning the electrochemical properties of the MIEC films by designing fine-grained columnar architectures.

La₂NiO₄ is a potential intermediate temperature solid oxide fuel cell (IT-SOFC) cathode material which belongs to the Ruddlesden-Popper (RP) structure series AO(ABO ₃ ) _n. There is interest in this material as it offers a way to avoid Sr segregation and associated degradation, as Sr doping is not essential. While the bulk ionic conduction mechanisms are well studied, its surface structure and chemistry are still a matter of debate. Recent experimental work (both with and without dopants) reveals it has a La-terminated surface and a highly Ni deficient surface layer [1]; this disagrees with earlier results from computer simulation, and undermines the conventional explanation for the oxygen reduction process at the surface. In this work we evaluate the thermodynamic stability of La₂NiO₄ at IT-SOFC operation temperatures. We find that the decomposition of La₂NiO₄ to produce La₂O₃ (no Ni) and higher order RP phases is indeed thermodynamically favourable. A hypothesis for the formation mechanism of the La-terminated and Ni deficient surface based on partial decomposition and surface passivation is proposed and evaluated.
1. Burriel, M., Wilkins, S., Hill, J. P., Muñoz-Márquez, M. A., Brongersma, H. H., Kilner, J.A., Skinner, S. J. (2014). Energy & Environmental Science, 7(1), 311.

Oxygen transport kinetics in mixed ionic-electronic conductors (MIECs) plays a key role in the efficiency and durability of solid oxide fuel cells and electrolyzers (SOFC and SOEC). In particular, the surface exchange at the solid-gas interface strongly determines the oxygen stoichiometry and the functional properties of perovskite and related oxides used as air electrodes in such electrochemical energy conversion devices.
Furthermore, the oxygen surface exchange might be drastically affected by the chemical composition and microstructure of these materials. Quite often the electrochemically-active surface and near-surface composition deviates significantly from the bulk, showing a very dynamic nature of the outer atomic layers after the thermal treatments typical in processing and operation conditions. For instance, segregation of intrinsic cations and/or extrinsic impurities might lead to a decrease of the active surface or the poisoning of the surface, while modifying its microstructure.
Nevertheless, our understanding of the oxygen surface exchange mechanism is still rudimentary. Addressing this problem requires surface-sensitive techniques that allow us to relate oxygen transport properties and the surface and interface chemistry of these electrode materials. To this end, we apply stable isotope labeling methodologies in combination with high surface-sensitive ion beam techniques, such as Time-of-Flight Secondary Ion Mass Spectrometry (ToF-SIMS) and Low-Energy Ion Scattering (LEIS. This approach has allowed us to reveal significant reorganization of the atoms at the outer surface of perovskite and perovskite-related materials, with a general trend to terminate the surface in an AO plane, contrary to what it is often modeled by DFT simulations.
Moreover, the kinetics of the surface reconstruction is extremely fast with the segregation of the constituent cations and impurities taking place in the short-term at low temperatures (i.e. Ba segregation in GdBaCo₂O_5+d occurs at 400°C after 15 min). This fast surface reconstruction has profound implications for the catalytic activity of the materials as it implies that the electroactive surface can drastically change from a mixed (AO)-, (A&’O)- and (BO_2shy;)- terminated surface (with different degrees of B cation coverage as the sample is annealed at low temperature) to an inactive or “blocked” surface where the transition metal completely covered by the A and A&’ cations.
The significant changes in the surface composition and morphology of these materials over the short time scales implies that the surfaces might even evolve within the timescale of a given isotope exchange depth profiling experiment. In this work we investigate the short-term surface evolution and its effects on the oxygen surface exchange process in perovskite and perovskite-related MIECs.

Stoichiometric chemical expansion, the gradual lattice dilation accompanying changes in stoichiometry (e.g. oxygen content), can lead to large stress generation during operation of solid oxide fuel/electrolysis cells (SOFC/SOECs), when components incorporate or release oxygen [1]. The release of oxygen forms oxygen vacancies (often with a slight lattice contraction) and electrons for charge neutrality (often localized on multivalent cations causing a much larger lattice expansion) [2]. In order to alleviate these stresses, deter mechanical failure, and thus prolong device lifetime, fundamental investigations into the factors controlling chemical expansion are needed. This talk will highlight recent studies of chemical expansion in perovskite-structured mixed ionic and electronic conductors used as, e.g., fuel/electrolysis cell electrodes.
In situ X-ray diffraction, dilatometry, thermogravimetry, and simulations (molecular dynamics and density functional theory) were applied to examine macroscopic and crystal-structure-level expansion of (La,Sr)(Ga,Ni)O_3-δ and Sr(Ti,Fe)O_3-δ in response to changes in oxygen partial pressure at high temperatures. In both cases, the coefficients of chemical expansion (CCEs) were found to depend upon the concentration of multivalent cation, which influences the degree of charge localization, and upon the temperature, which may relate to the extent of ordering or bond strengths. For example, in (La,Sr)(Ga,Ni)O_3-δ the CCE was lowered ~20% at 900 °C by increasing the Ni content from 0.05 to 0.5 [3], thereby delocalizing charge as shown by electrical measurements [4], and supporting prior theoretical results indicating decreased chemical expansion upon charge delocalization [2]. In Sr(Ti,Fe)O_3-δ the CCE was lowered ~20% by decreasing the temperature from 1000 to 700 °C.
The two systems differed in other aspects. Subtle increases in crystal structure symmetry were observed during chemical expansion in the rhombohedral (La,Sr)(Ga,Ni)O_3-δ; such crystal-structure-level anisotropy of the expansion process represents another variable that may be tuned to influence macroscopic expansion in polycrystalline electrodes. Finally the effective size of an oxygen vacancy was found to differ between the two systems; this contraction around the vacancy should be enhanced to further lower the chemical expansion coefficients and enhance electrode durability.
[1] SR Bishop et al., Ann. Rev. Mater. Sci. 44 (2014), Online
[2] D Marrocchelli et al., Phys. Chem. Chem. Phys. 14 (2012) 12070
[3] NH Perry et al., ECS Trans., 57 (2013) 1879
[4] NJ Long et al., J. Electroceram. 3 (1999) 399

La_0.6Sr_0.4Co_0.2Fe_0.8O_3-δ (LSCF) is a promising mixed-conducting cathode for solid oxide fuel cells (SOFCs) due to its catalytic activity. The oxygen reduction reaction at the cathode surface is a rate-limiting step in SOFC performance; however, many details of the reaction are not clear. In particular, understanding the oxygen exchange properties between the cathode and the atmosphere and between the electrolyte and cathode is crucial to optimizing cathode materials.
In the current work, synchrotron x-ray diffraction was used to study the oxygen exchange reaction of LSCF pseudo half-cells in situ during cell operation. The cells consisted of a thin film of LSCF (60 nm) grown by pulsed laser deposition on a yttria-stabilized zirconia (YSZ) substrate, with a gadolinium-doped ceria (GDC) buffer layer. Local changes in the LSCF oxygen vacancy concentration in response to an applied electrochemical bias were inferred from lattice parameter changes measured by x-ray diffraction. A model was developed to determine the reaction constant for oxygen exchange across the cathode/electrolyte interface based on these local changes in oxygen vacancy concentration. This analysis was used to study the effect of operating conditions (temperature, pO₂, and atmosphere composition) on oxygen transport in LSCF cathodes. Implications of these results on SOFC cathode performance will be addressed.

Composites of 8 mol% yttria-stabilized zirconia (YSZ) and titaniun nitride (TiN) were fabricated. Such composites exhibit interesting mechanical and electrical properties and have been investigated for different high-temperature applications. Commercially available starting powders of YSZ (Tosoh, Japan) and TiN (Sigma-Aldrich) were mechanically mixed in a ball-mill using zirconia-based balls and ethanol. After drying under mixing, composite powders YSZ / w TiN, with relative weight fractions w = 0, 25, 50, and 75% of TiN were analyzed by X-rays diffraction (XRD). Samples were sintered by spark plasma (SPS) using graphite dies and punches (14 mm diameter), which were covered with a carbon paper to avoid direct contact with the samples. Maximum SPS temperature was 1450 °C for 5 min, with 100 °C min^-1 heating rate and applied pressure of 30 kN cm^#8209;2 up to 1250 °C and 60 kN cm^#8209;2 for higher sintering temperatures. Final samples dimensions were ~14 mm diameter and 1 mm thickness. Estimated apparent densities were ~98% of the theoretical density calculated by the rule of mixtures. The sintered pellets were analyzed by XRD. The XRD data revealed a pronounced superficial carbon contamination, as usually observed in SPS. However, in the present composite the covalent nature of TiN rules out carbon removal by thermal treatment. Indeed, the carbon oxidation was confirmed by thermogravimetric analysis to occur at temperatures higher than the conversion of TiN into TiO₂ (~500 °C). Therefore, YSZ/TiN pellets were mechanically rectified in a diamond saw, which removed ~300 µm of each parallel surface of the samples. Rectified pellets were analyzed by XRD and only the characteristic diffraction lines corresponding to YSZ and TiN were found, indicating that significant carbon diffusion was limited to thickness < 350 µm. Moreover, by comparing the XRD data before and after SPS indicated that no significant reaction between the phases occurred.

Sr- and Mg-doped lanthanum gallate is a perovskite oxide ion conductor with high ionic conductivity compared to yttria-stabilized zirconia. This solid electrolyte is a promising material for application in solid oxide fuel cells operating at intermediate temperatures (~500-700°C). In this work, the effects of the sintering profile on the ionic conductivity and microstructure evolution were systematically investigated. The nominal composition La_0.9Sr_0.1Ga_0.8Mg_0.2O_3-d was prepared by solid state reaction. After calcination at 1250°C, the powder mixture was pressed into pellets and fast fired at 1450°C for 5 and 10 min, and at 1500°C for 5 min. The X-ray diffraction patterns show typical reflections of the orthorhombic perovskite-type structure along with few reflections due to secondary phases, SrLaGaO₄, La₄Ga₂O₉ and SrLaGa₃O₇. Fast fired specimens at 1450°C for 10 min exhibited negligible secondary phases. The sintered density increases with increasing dwell temperature and time. The mean grain size varied from 2.3 to 3.4 µm. The grain conductivity is unchanged with the dwell time but decreases with increasing the dwell temperature. The grain boundary blocking effect is lower for specimens fast fired at 1450°C for 10 min, probably due to the negligible fraction of secondary phases of these specimens.

During the past years, solid oxide fuel cells (SOFC) technology is approaching commercial application, and thus, the development of long-term durability and stability SOFC is attracting increasing interest from the energy sector [1]. In order to reduce costs and enhance the SOFC performance, the understanding and dismissing of degradation mechanisms under operating conditions is becoming an essential need. Some of these degradation mechanisms are related to contact issues, such as the delamination of an electrode from the electrolyte or the lack of contact between the interconnect and the electrode, which cause an important increment of the ohmic resistance. Furthermore, there exist various issues that originate from the cell components, including the decrease in the intrinsic electrical conductivity of YSZ-electrolyte, coarsening of nickel particles in the anode or poisoning the cathode by Cr species from the metallic interconnects [2]. The objective of the SAFARI project is to understand these mechanisms to improve the efficiency of the militubular SOFCs, being the final goal to apply the mSOFC technology for auxiliary power supplies on trucks fed by LNG.
In this work , the degradation performance of single militubular SOFCs cells ( LSCF/YSZ/Ni-YSZ) has been carried out under different H2 fuel utilizations and constant current conditions of 6 A, at 7000C during 500 hours. During operation, the electrochemical characterization was accomplished by means power density and impedance spectroscopy measurements. Moreover, post-mortem x-ray diffraction and SEM analysis have been realized in order to evaluate the microstructural evolution of Ni/YSZ anode and the presence of possible secondary phases or impurities.
References:
[1] C. Comminges, Q.X. Fu, M. Zahid, N. Yousfi Steiner, O. Bucheli, Electrochimica Acta, 59, 2012, 367-375
[2] H. Yokokawa, H. Tu, B. Iwanschitz, A. Mai, Journal of Power Sources, 182, 2008, 400-412
[3] K Kendall, A Meadowcroft, Int J Hydrogen Energy 38, 2013, 1725-1730

The oxidation of CO to CO₂ is necessary in the operation of Proton Exchange Membrane Fuel Cells (PEMFCs) since even a small amount of CO that is formed when the PEMFC is operated under ambient conditions is sufficient to poison the Pt catalyst in the electrodes and degrade the performance. Operation using higher loads of Pt catalysts or increasing the purity of the H₂ input gas significantly adds to the cost, adversely impacting the commercial development of PEMFCs. We have developed a new method for reducing graphene oxide with metallic salts that yields a metalized form of graphene platelets. When these platelets were coated on the Nafion membrane of PEMFC, a nearly 150% increase in the efficiency was observed, whereas a slight decrease in efficiency was observed when the membrane was coated with graphene oxide reduced in the absence of the metallic salts. In order to understand the mechanism involved we further investigated this reaction by varying the parameters such as the nature of the metallic salts, the concentration, and any synergies when more than one type of metallic salt was used. Results will be presented for AuRGO, PtRGO, AgRGO and AuPt alloys.

Today the solid oxide fuel cells (SOFCs) are envisaged as one of the most efficient devices for providing clean energy through the exploitation of renewable sources. The main challenges for their development as eco-friendly technology are: i) reducing the operating temperature from ~1000°C (HT) to ~500-800°C (IT); and ii) using renewable fuels such as natural gas or biofuel [1]. To achieve these purposes, it is essential to seek new electrode and electrolyte materials characterized by appropriate features. In particular, anode materials must be able to effectively catalyze fuel oxidation, avoid surface poisoning, and show good mixed ionic-electronic conductivity. Among other candidates, it has been recently observed that La_1-xSr_xCr_1-yFe_yO_3-δ perovskite-type oxides have suitable properties as potential anodes for IT-SOFCs fed with hydrogen [2] or methane [3]. In order to extend the knowledge about the role of iron doping in LaCrO₃-based perovskite-type compounds, a series of La_1-xSr_xCr_1-yFe_yO_3-δ (0le;xle;0.2; 0le;yle;0.5) was prepared by solution combustion synthesis. The catalytic activity was evaluated through temperature programmed reduction measurements under three different conditions: 1) CH₄(0.3%)/He; 2) CH₄(3%)/He and 3) CH₄(3%)/H₂S(150ppm)/He. The experiments revealed the ability of the materials to consume methane mainly through two distinct processes that, on the basis of the evolved gases, are ascribable to: i) total methane oxidation to (CO₂+H₂O) between ~500-600°C ; and ii) partial methane oxidation to (CO+H₂) above ~700°C. It is worth noting that the methane conversion was achieved also in presence of a more concentrated reaction mixture and of H₂S. Among the investigated compositions, La_0.85Sr_0.15Cr_0.5Fe_0.5O_3-δ was the most active material, but this compound exhibited a limited electrical conductivity, as measured in d.c. regime with the four probe method. Actually, electrochemical impedance spectroscopy tests on membrane-electrode assemblies (Pt/Ce_0.8Sm_0.2O_2-δ/doped-LaCrO₃) fed with O₂(cathode)/H₂(anode) pointed out that La_0.9Sr_0.1Cr_0.7Fe_0.3O_3-δ exhibited the lowest polarization resistance, as well as the lowest overall resistance between 600-800°C. In conclusion, a systematic investigation carried out as a function of iron doping allowed us to assess that the La_0.9Sr_0.1Cr_0.7Fe_0.3O_3-δ composition represents the best compromise between catalytic activity and electrical performance.
References
[1] Brett, D.J.L.; Atkinson, A.; Brandon, N.P.; Skinnerd, S.J. Chem. Soc. Rev. 2008, 37, 1568.
[2] Fowler, D.E.; Haag, J.M.; Boland, C.; Bierschenk, D.M.; Barnett, S.A.; Poeppelmeier, R. Chem. Mater. 2014, 26, 3113.
[3] Danilovic, N.; Vincent, A.; Luo, J.L.; Chuang, K.T.; Hui, R; Sanger, A.R. Chem. Mater. 2010, 22, 957.

Impedance spectroscopy (IS) is the most commonly used technique for studying conductivity of ionic and mixed ionic/electronic conductors. Though being simple and versatile, it has the disadvantage of inability to distinguish between ionic and electronic charge carriers at a fixed chemical composition. In addition, the interpretation of IS spectra is not unambiguous. We propose a technique based on null-ellipsometry with lock-in detection, which can distinguish between ionic and electronic carriers. It monitors changes in refractive index caused by ion migration due to applied voltage. Using this technique, we determined the activation energy of oxygen ion diffusion (E_A^ion) in thin films of 20mol% Gd-doped ceria with columnar grain structure between 100°C to 160°C. In parallel, we measured the same film with IS, both along and across grain boundaries. The optical technique yields E_A^ion=1.5±0.1eV, whereas IS yields activation energies of 0.4eV along, and 0.8eV across, the grain boundaries. This difference demonstrates the inability of IS to properly account for effects such as anisotropic grain boundaries and presence of more than one conduction mechanism. We conclude that the optical technique is the more reliable probe of grain core ion diffusion in thin films.

We investigated defect segregation and space charge layer formation at nonstoichiometric BaZrO₃ (210)[001] tilt grain boundary. To obtain an energetically more stable grain boundary, we considered nonstoichiometry at grain boundaries. Among two stoichiometric and four nonstoichiometric grain boundaries that were considered to find an energetically stable grain boundary, the BaZrO₃-terminated nonstoichiometric grain boundary was the most stable. Two positively charged defects, a proton and oxygen vacancy, were segregated at the grain boundary with segregation energies of -1.23 and -0.50 eV, respectively. The oxygen vacancy was less segregated at the grain boundary when it competes with the proton owing to the stronger segregation of the proton. Space charge layers were developed at the grain boundary due to the segregation of the proton. Proton interaction at the grain boundary was considered to fine-tune the space charge layer.

Monoclinic monazite (LaPO₄) doped with divalent elements such as strontium (Sr²⁺) is a good material candidate for electrolytes in intermediate temperature proton conducting solid oxide fuel cells (SOFC). Synthesis of monoclinic monazite by solution routes usually results in the production of a hexagonal hydrate, rhabdophane (LaPO₄.1/2H₂O). Rhabdophane engenders liquid phase formation within samples during sintering at high temperatures due to presence of excess phosphorus. Availability of liquid phase at high temperatures detrimentally scavenges Sr²⁺ from the doped monazite. Circumventing the formation of rhabdophane should improve the efficiency of proton conduction of the derived material.
In this study, monoclinic LaPO₄, with up to 30% Sr²⁺ doping, has been synthesized using a direct precipitation synthesis, without any formation of rhabdophane, as investigated by XRD. The morphology of the precipitated powders, under differing conditions of doping and temperature, is seen using SEM. Also, the possible presence of excess phosphorus, even in the absence of rhabdophane, is investigated through sintering the samples at 1500°C by using SEM. Lastly, the stability of monoclinic Sr²⁺ doped LaPO₄ is compared in dry and humid environment by sintering and annealing in air and in the presence of water vapor, by XRD. Formation of the secondary phase, Sr(PO₄)₂, is obtained as a result of sintering in the absence of water vapor.

Proton conductive Ba(CeZr)O₃ (BCZ) ceramics are, recently, reported that the chemical stability can be greatly improved by co-doping with Y and Yb under CO₂ and H₂O atmospheres (L. Yang et al., Science, 326 (2009) 26). Various researches on the BCZ ceramics have been energetically conducted due to a promising candidate as an electrolyte material for SOFC/SOEC applications. However, there are few reports on the relationship between thermal and electrochemical properties in Y and Yb co-doped BCZ material. In this study, we will show the electrical conductive and crystallographic characteristics of sintered BCZ ceramics.
Ba(Ce_0.7Zr_0.1Y_0.1Yb_0.1)O₃ (BCZYYb) were mixed with 0-10 wt% of NiO as a sintering additive. The pressed BCZYYb compacts were sintered from 1200 to 1400°C for 2h in air. The density and open porosity were measured by Archimedes method. The electrical conductivity and crystal structure of the sintered samples were evaluated by using DC four-terminal method and XRD measurement. Thermomechanical analysis (TMA) was also performed.
The solubility limit of NiO in the BCZYYb can be estimated to be in the range of 5-10 wt%. The maximum values were 13.4×10^-3 and 9.3×10^-3 S/cm at 600°C in dry air and humidified hydrogen atmospheres, respectively. The activation energies derived from Arrhenius plots of those conductivities are approximately 0.6 and 0.5 eV under the same conditions.

Over the past two decades, polymer electrolyte membrane fuel cells (PEMFC) have received new interest due to potential applications in the automotive, power transfer and electrical industries. For this, the membrane of choice is DuPont&’s Nafion. A co-polymer of terminally-bound sulfonate ether chains on an ether backbone, water retention is high thus facilitating superior proton mobility along the arrays of hydrophobic water channels that are formed via self-assembly. Whilst performing admirably at temperatures less than 80 °C, as the optimal temperature for PEMFCs is approached conductivity begins to plummet due to dehydration of the Nafion matrix. Many approaches have been employed to circumvent this problem but to date none of them have been successful enough to warrant commercial application. Herein we discuss research into the initial and subsequent optimisation of materials that are resistant to dehydration at higher temperatures and in low humidity environments.
Initial research into this system utilised high surface area mesoporous Ti oxide as a basis; to which its mesopores were impregnated with a sulfonated oligomer, naphthalene sulfonate formaldehyde (NSF). Formed into a pellet and heated to 100 °C, a proton conductivity of 1.837 mS cm^-1 was recorded that surpassed a similarly-formed pellet of Nafion 117 (1.143 mS cm^-1).¹ This system was subsequently optimised by changing the metal oxide (to that of Nb and Ta) and the pore size (by changing the template to that of a differing carbon chain length). The most promising sample displayed a proton conductivity of 21.96 mS cm^-1 at 100 °C,² surpassing the literature value of a Nafion membrane (8 mS cm^-1) and that of pure hydrated NSF (0.122 mS cm^-1), confirming a synergistic interaction between the NSF and the oxide mesostructure in the proton conductivity mechanism.
Turley. J. P., Romer. F., Trudeau. M. L., Dais. M. L., Smith. M. E., Hanna. J. V., Antonelli. D. M., Microporous Mesoporous Mater., 2014, 190, 284-291
Turley. J. P., Romer. F., Trudeau. M. L., Dais. M. L., Smith. M. E., Hanna. J. V., Antonelli. D. M., In Press., 2014

Bulk Lithium Dihydrogen Phosphate, LiH₂PO₄ (LDP), has been shown to be a superprotonic conductor. As with many materials related to fuel cells, the task of transforming LDP performance from bulk to useable films poses significant challenges, e.g. thickness, uniformity, and creating 3D devices. Additionally, in most proton conducting devices costly platinum is used as the catalyst. In the present work, we describe the fabrication of inkjet printable inks used to create a proton conducting device: nickel ink for the catalyst and LDP ink for the proton conducting membranes. Electrochemical impedance spectroscopy (EIS) was performed over a range of temperatures and equivalent circuit modeling was performed. The conductivity extracted from this model was of the same order as the bulk conductivity of LDP (2 × 10^-2 S / cm^-1). Protonic conduction was conclusively shown by using a hydrogen atmosphere. The nickel printed films showed excellent electrical conductivity. Morphological examination of the device by scanning electron microscopy (SEM) revealed densely packed LDP layers well suited to proton conduction and porous nickel layers ideal for hydrogen catalysis. The conduction mechanism of the protons through the device was modeled, examining interfacial, bulk, and surface reactions. These correlated to experimental conductivity values. Future work, using the extension of this computational model as a blueprint, will be discussed.

Dual phase composites containing a mixed ionic and electronic conductor (MIEC) and an ionic conductor are used in both solid oxide fuel cell cathodes and oxygen permeation membranes. The oxygen Surface Exchange Reaction (SER) in these composites is believed to primarily occur at the surface of the MIEC, whereas the ionic conductor transports parts of the oxide ions. Recently, it has been reported that the SER of a composite is significantly enhanced compared to what could be expected if the SER is occurring only on the MIEC¹. The rate of the SER is very important for the performance of electrochemical devices and it is therefore important to understand the interplay between two materials and its effects on the overall achievable oxygen incorporation rate.
In the present work Electrical Conductivity Relaxation (ECR) has been used to study the SER and the oxygen ion diffusion, in dual phase composites of (La_0.6Sr_0.4)_0.98FeO_3-δ/Ce_0.9Gd_0.1O_1.95 (LSF/CGO). The results have been compared to those of single phase LSF. ECR is a well-established method to determine the oxygen transport properties of MIEC. ECR is based on recording the change of conductivity versus time after an instantaneous change of oxygen partial pressure (pO₂) in the surrounding gas. Due to the change of pO₂ a new equilibrium of oxygen vacancies in the sample is established, which results in a characteristic change of conductivity with time. The response of conductivity can, by using Fick&’s Laws of diffusion with appropriate boundary conditions, be fitted to obtain the oxygen surface exchange coefficient (k_ex) and the chemical diffusion coefficient (D_chem).
The effect on catalytic and charge transport properties was studied by preparing samples containing 70/30, 50/50, 30/70 and 100 vol% CGO/LSF. The D_chem was found to be in the range from 2.73 10^-5 (100% LSF) - 1.24 10^-3 cm²/s (70/30 CGO/LSF) and the k_ex was found to be in the range 3.51 x 10^-5 (100% LSF) -1.86 x 10^-4 cm/s (70/30 CGO/LSF) at 750°C and pO2 = 1.00 atm. The measurements clearly show that the dual phase composites containing 70/30 vol% CGO/LSF shows superior transport properties. The increase in the k_ex for the sample containing the most CGO is somewhat surprising as CGO is believed not to be a good electrocatalyst for oxygen reduction. Measurements at different temperatures between 600°C and 900°C reveal that the temperature has a large influence on the enhancement of the k_ex for the composites. The highest enhancement was measured at the lowest temperature. For the composition containing 70/30 vol.% CGO/LSF different samples with the same surface area ratio of CGO/LSF but different Triple Phase Boundary (TPB) length were prepared. The results clearly demonstrate that the surface exchange rate does not depend on the TPB length. The reasons for the enhanced exchange rate observed for composites as well as its technological consequences will be discussed.
1. Wang Y, et. al, J Mater Chem A. 2 (2014) 136-143.

The ever-growing demands for advancement in reliability, robustness, and endurance of low-cost solid oxide fuel cells (SOFCs) have stimulated great interest in developing SOFCs with a low degradation rate. In SOFCs, degradation may originate from myriad physical sources, with thermal, electrostatic, and chemical potential drivers being particularly prominent. Electrochemical reactions take place at the triple-phase boundaries (TPBs) between the electrolyte, the electrode and the gaseous reactant, and small changes in TPB structure or chemistry, and the interface between electrode and electrolyte can drastically affect SOFC performance and lifetime. However, very limited experimental work has been reported on the nanostructure and chemistry evolution of the interface and TPBs in the SOFC upon cell operation, especially upon long term operation of over 1500 hours. The present work employed Transmission Electron Microscopy (TEM) to investigate the nanostructure and chemistry of the grain boundaries and interfaces, including TPB in both anode and cathodes of SOFC, over the long term operation of 3000 hours and 1500 hours.
To investigate the origin of anode degradation, the evolution of grain boundary and interface nanostructure and chemical composition were systematically examined. For the commercial MSRI button cells operated at 0.6A/cm², over 300 hours operation, the electrochemical data show increased polarization resistance and decreased power density. Accompanying the electrochemical performance degradation are significant nanostructure changes observed at the YSZ/YSZ grain boundaries in the anode. Nano-scale void-like features were observed at the YSZ/YSZ grain boundaries from the cell operated for 3000 hours. The observation starkly contrasts with the as-received cell, which possesses intact boundaries between the YSZ/YSZ grains. The voids were oval shaped with a long axis of ~30nm, and were discretely distributed across the grain boundary planes. TEM observations over several tens of different YSZ grain boundaries from the active layer of anode consistently indicate that the void-like features are common in the cell operated for 3000 hours. The nano-structure and chemistry of those void regions at the YSZ/YSZ grain boundaries, and the origin of their formation and the possible impact on the overall cell performance are discussed.
For the cathode of commercial cells, cathode infiltration of nanomaterials has been proven to be effective in introducing eletro-catalyst to the intrinsically functional electrodes and enhancing the performance of the as-prepared SOFCs. However, limited fundamental research has focused on study of the stability of such infiltrated nano-particles upon long-term operation. In the present study, the nanostructure and chemistry of the infiltrated La_0.6Sr_0.4CoO₃ electro-catalyst and its evolution upon operation were analyzed by TEM for cells that were electrochemically characterized under industrially relevant conditions.

Al, Hf, Zr, Ta, Nb, Ti, and W are classified as valve metals because their oxides have evident rectifying properties. Self-organized array of nanotube nanomaterials produced by electrochemical anodization of various valve metals combined with an electropolishing step have been a great deal of interest due to unique geometrical structures, facile fabrication process, economic feasibility, and a wide range of applications in the field of nanosciences and energy. The formation of self-organized regular arrays of oxide nanotubes lies in a delicate balance between the oxide growth rate and the oxide etching rate and a lattice mismatch between the grown metal oxide and the underlying valve metal. The requisites for their fabrication are the electropolishing and a two-step anodization. The most uniform and self-organized regular arrays of anodic valve metal oxide nanotubes are formed by the process consisting of electropolishing and a two-step anodization. Our findings can be generalized to fabricate self-organized regular arrays of other valve metal oxides. The highly regular arrays of anodic Al₂O₃, ZrO₂, TiO₂ nanotubes were achieved with our process. We applied these nanoporus materials for the electronic and energy-related devices. We were able to fabricate high-density arrays of individually isolated nanocapacitors with anodic aluminum oxide. ZrO₂ has been utilized as a component in an oxygen sensor or as solid electrolyte membranes in solid oxide electrolyte fuel cells (SOFCs). TiO₂ nanotubes were used as a photoanode in the photolysis of water or solar energy conversion. To expand the photocatalytic activity of TiO₂ to visible light, doping of transition metals or non-metal atoms such as C, N, and S into TiO₂ was done. Or TiO₂ photoanodes fabricated with the regular array of TiO₂ nanotubes anchored with CdS/CdSSe/ZnS quantum dots were prepared for highly efficient solar energy conversion. We&’ve been working on solar energy conversion or water splitting with doped or QDs-anchored TiO₂ nanotubes and have made much progress.

LaNi_(1-x)Fe_xO₃ (0.0 le; x le; 0.4) compounds have interesting physical properties such as high ionic and electronic conductivity, good catalytic activity for oxygen reduction, and thermodynamic compatibility with the YSZ electrolyte, which makes them potential candidates for SOFCs cathodes. Order for these excellent properties are achieved, it is necessary to ensure the presence of the homogeneous phase LNF. The methods for preparing these compounds influence the formation and retention of the homogeneous phase and therefore the physical properties of these oxides. For this reason, this work deals with the synthesis of the family of compounds LaNi1-xFexO3 (0.0 le; x le; 0.4) and the correlation between the synthesis and the physical properties obtained. In this context, LaNi1-xFexO3 (0.0 le; x le; 0.4) compounds were synthesized by a modified Pechini method for production of powders. Two different synthetic routes was employed, changing the source of nickel: nickel acetate and nickel nitrate. In order to study the thermal evolution of the LNF phase in these compounds, thermal analysis (DTG) and DRX were performed. The X-ray diffraction was verified that the series of compounds synthesized by nickel acetate originated monophasic samples different from those obtained with nickel nitrate. The viability of applying these oxides prepared from Ni and Fe acetates in electrodes of the SOFCs was investigate the influence of time and sintering temperature on the dimensions of the pellets and densification. The conditions for sintering, the powders were analyzed by X-ray diffraction, and thermal analysis. In these studies, it was observed the reduction in sintering time allowed obtaining powders of perovskite phase, with grain sizes and smaller clusters than what was observed in the compound -treated for 10 h. To characterize the particle size, the powders were characterized by curves absorption/desorption (BET). The results also show that heat treatment for shorter times resulted in decreased particle size as well as increase the surface area of the compounds.

Although solid oxide-based electrochemical devices are advantageous over other low-temperature devices in terms of energy efficiency, system complexity and fuel flexibility, their high operational temperature (usually > 800 °C) limits the system durability, device applicability and cost-competitiveness. Reduction in operating temperature is unfortunately followed by a significant sacrifice in the electrode kinetics, but sustaining decent electrode kinetics, especially oxygen reaction rate, at lower temperatures using conventional oxide electrodes remains as a challenge. Although platinum has been known as the best air electrode for low temperature operation, porous metal electrodes tend to degrade over time due to Ostwald ripening, resulting in significant cell performance degradations. More importantly, their availability is limited and the price is also prohibitive to be widely used.
Recently, graphene-based electrodes, especially nitrogen-doped graphene, have been applied to low temperature fuel cells (mainly polymer electrolyte membrane fuel cells) as the cathode material and showed remarkable catalytic performances. In addition, graphene is reported to have superior charge mobility, mechanical strength, flexibility and thermal stability. These advantageous properties suggest the promise of graphene-based materials as the air electrode of electrochemical energy devices, even operating at elevated temperatures. In this talk, we specifically present the feasibility of using graphene derivatives as the air catalyst of low temperature solid oxide cells operating below 400 °C.
We fabricated thermally reduced graphene oxide (GO) and N-doped GO samples and characterized their material stability and electrochemical performance at the temperature range of 225 - 400 °C in atmospheric air. N-doped GOs are found to exhibit a remarkable catalytic performance of oxygen reaction at the temperature regime, close to that of platinum. Furthermore, they showed little degradation over time (at least for 8 hours) unlike porous metal-based electrodes. The thermal stability was supported by the fact that none of the interlayer distance, defect concentration, morphology and N content changes appreciably at elevated temperatures up to 400 °C in air. On the other hand, metal electrodes change their morphology at high temperatures by agglomeration, which would have a significant impact on their overall catalytic activities. We can expect an even better performance by further engineering on the size and distribution of graphene flakes, electrolyte-graphene interface and so on. The widespread availability of carbon and prospective cost competitiveness through mass production additionally favors these graphene-based derivatives as an alternative to the conventional noble metal-based air electrodes operating below 400 °C.

Solid oxide fuel cell cathode materials with mixed ionic and electronic conductivity (MIEC) such as strontium doped lanthanum cobalt oxide (La_0.6Sr_0.4CoO_3minus;δ) show enhanced oxygen reduction kinetics compared to the conventional cathode materials [1]. Several studies have evidenced that oxygen reduction kinetics are governed by the oxygen exchange at the perovskite/air interface for MIEC cathodes [1,2]. Thus, the electrochemical performance of the cathodes with MIEC may be enhanced by providing a larger area for oxygen exchange either by increasing the electrode thickness or by reducing the grain size. Therefore, cathodes having nanoparticulate microstructure have been considered as their high surface area to volume ratio creates a large number of reaction sites for oxygen exchange.
Nanocrystalline La_0.6Sr_0.4CoO_3minus;δ (LSC) powder with ultrafine microstructure and high specific surface area (60 m²/g) was synthesized via a salt-assisted spray pyrolysis method. Nanoparticulate cathode thin films of LSC with thicknesses below 1 micron were prepared via single-step spin coating of water-based nanodispersions on yttria stabilized zirconia (YSZ) substrates. In order to prevent undesired reactions between cathode and electrolyte, a gadolinium-doped ceria (GDC) thin film was deposited as an interlayer on the YSZ substrates. Electrochemical characterization of the symmetrical cells was conducted via Electrochemical Impedance Spectroscopy (EIS). The lowest polarization resistances of LSC cathode thin films are 0.09 and 0.24 Omega;.cm² in ambient air at 600 and 550 ^#8728;C, respectively. Furthermore, nanoparticulate-based LSC cathodes with a thickness of 250 nm were integrated via single-step spin-coating on free-standing yttria stabilized zirconia (YSZ, 300 nm) electrolyte membranes prepared by pulsed laser deposition. Platinum films (80 nm) sputtered on the back side of the electrolyte serve as anodes and complete the fabrication of a silicon-based micro-SOFC. First power density data of 12 mWcm^-2 at 500 ^#8728;C were obtained, thereby demonstrating that spin-coating of nanoparticulate suspension is a reliable method to fabricate cost-effectively micro-SOFC components [3].
[1] J. Hayd, L. Dieterle, U. Guntow, D. Gerthsen, E. Ivers-Tiffee, J. Power Sources 2011, 196, 7263-7270.
[2] F. S. Baumann, J. Fleig, H.-U. Habermeier, J. Maier, Solid State Ionics 2006, 177, 1071-1081.
[3] A. Evans, C. Benel, A. J. Darbandi, H. Hahn, J. Martynczuk, L. J. Gauckler, M. Prestat, Fuel Cells 2013, 13, 441-444.

Solid oxide fuel cells (SOFCs) are one of the most promising alternatives for power generation systems due to their high efficiency and fuel flexibility. In particular, unique capabilities of utilizing any kind of fuels in SOFC systems have been emphasized the direct utilization of hydrocarbon fuels without external reformer for converting to hydrogen fuels. If methane, which is the major constituent of natural gas, could be utilized directly in SOFC systems, the currently available infrastructures of city gas can be implemented for highly efficient SOFC systems. Nonetheless, carbon coking on nickel-based anodes and relatively low efficiency for direct methane-fueled SOFCs still relegate these systems to immature technologies. Here, we introduce the novel direct hydrocarbon fueled SOFCs operating by partial oxidation (POX) of methane. Co-feeding of oxygen to anode leads to partial oxidation of methane, which eliminates the deposition of carbon on nickel catalysts fundamentally and facilitates the oxidation of methane fuels. Conventional anode supported cells using conventional materials of Ni-yttria stabilized zirconia (YSZ) are tested under methane-oxygen mixture gas at 800 ^oC to investigate the feasibility of POX operation. Electrochemical analyses and gas chromatography (GC) reveal that the cell operates via POX of methane. Furthermore, carbon deposition can be suppressed significantly when oxygen is supplied simultaneously with methane as compared to the operation under methane only. Finally, Ni-gadolia doped ceria (GDC) and based cells exhibits the maximum power density of 0.90 Wcm^-2 at 650 ^oC, which maintains over 200 hours. While Ni-yttria stabilized zirconia (YSZ) cells represents 0.27 Wcm^-2 at 650 ^oC and subsequent degradation of the powder density is observed. Chemical states analyses of Ni catalysts via X-ray photoelectron microscopy, conductive atomic force microscopy and X-ray adsorption spectroscopy suggest that juxtaposing GDC as a support prevents Ni catalysts from oxidation by oxygen storage capability of GDC. To confirm the prevention of carbon coking by POX on stainless steel current collectors for SOFC stacks, stainless steel mesh was employed as a current collector for anodes. Elemental analyse of the current collector after POX operation also showed the depression of carbon deposition by POX. These results demonstrates that durable and high-performance SOFC systems directly utilizing methane with Ni-based anodes can be achieved via operation based on partial oxidation without deterioration by oxidation of metal catalysts.

During thermal cycle, in order to define thermal stress and sealant deformation ratio (which is source of fuel leak), thermo-mechanic model has been developed between 300-973 K for SOFC interconnect, sealant and electrolyte. Thermo-mechanic and thermo-physical properties were found via dilatometer, DSC, bending tests and properties were used in the model. The model was solved numerically and it was found that the highest temperature difference was occurred when the stack temperature first reached to 973K and in that time sealant interface stresses in the outer surfaces were found higher than the inner. Also stress distributions throughout of thermal cycle was computed. At the beginning of heat-up, stress in the sealant inner surface is higher than the outer surfaces while stresses in the outer surface is higher than the inner surface at the temperatures close to 973K and the stresses in the sealant interfaces have exceeded deformation strength at 973K. As another result stresses caused by the temperature differences are dominant at the low temperatures while stresses caused by the CTE differences are dominant at the high temperatures.

The reaction of oxygen at the cathode surface forms an integral part of the operation of a fuel cell device. We present a systematic synchrotron X-ray photoemission investigation of the reaction of oxygen molecules with La_0.6Sr_0.4Co_0.2Fe_0.8O_3-δ surfaces at low-intermediate temperatures (<300^oC) and low partial pressures (~10^-8torr) of oxygen. For the purpose of comparison annealing experiments are also carried out in inert Ar atmosphere. Our results indicate that annealing in Ar results in the removal of carbon contamination resulting in atomically clean LSCF surface, whereas annealing in oxygen environment prevents carbon desorption. A multi-peak fitting procedure in conjunction with angle of emission measurement is used to identify the peak components of strontium and oxygen core-levels which show difference in temperature dependence for the formation of oxygen vacancies in LSCF when annealed in Ar and O environment. We observe an insulating transition at 300^oC. The difference in the observed transition for the two different annealing gases used and the species responsible for the transition will be discussed.
Acknowledgments
The present work is supported by the U.S. National Science Foundation grant no. CHE-1213381. The authors would also like to thank Dr. Tiffany Kaspar, scientist at Pacific Northwest National Laboratory, Richland, WA for Pulse Laser Deposition growth of LSCF samples.

Atomic scale modelling suggests that excess oxygen can be accommodated in the group II perovskite zirconates by the formation of peroxide ion defects. This is unprecedented given the lack of charge compensating defects available for standard excess oxygen accommodation. Solution of O₂ was predicted to be close to zero (very favourable) for BaZrO₃, accommodating the defect more easily than in SrZrO₃ or CaZrO₃. This was experimentally examined by exposing SrZrO₃ and BaZrO₃ to hydrogen peroxide solution and then carrying out Raman spectroscopy to identify a possible peak due to a different bond type, indicative of a peroxide ion. A peak was observed at 1000 cm^minus;1 in both compositions suggesting the theoretically predicted peroxide ion is present. The ease of peroxide defect formation suggests that it is the dominant defect in this oxide system and it will likely dominate in a range of other oxides where cation oxidation is difficult (including group II oxides and some fluorite dioxides).

Intermediate-temperature solid oxide cells (IT-SOCs) have substantial advantages for efficient grid-scale electricity storage, but cells with unusually low polarization resistance are required. High-performance IT-SOCs were fabricated with thin LSGM electrolyte and Sr_0.8La_0.2TiO_3-α (SLT) oxide support. The novel process employed was to first co-fire tape-cast ceramic layers - porous SLT support, porous LSGM layer, and dense LSGM layer - followed by infiltration of nano-scale Ni into the porous layers. The effect of fuel electrode functional layer porosity and Ni loading amount on the cell performance was investigated. Total resistance as low as of 0.18 Omega;cm², measured at 650^oC in air and 50% H₂ / 50% H₂O, was achieved for a cell with an optimized fuel electrode functional layer and a (La,Sr)(Fe,Co)O₃ - Gd-doped Ceria composite cathode. Maximum fuel cell power density reached 1.6Wcm^-2 at 650^oC. Reversible electrolysis and fuel cell operation was investigated under different H₂O steam compositions. With 50vol.%-50vol.% H₂, the overpotential was only 0.07V at 0.5Acm^-2 at 650^oC. Cell life tests results obtained under galvanostatic electrolysis operation under different current densities will be presented.

Segregation of strontium from the lattice of the La_1-xSr_xCo_0.2Fe_0.8O_3-δ cathodes and formation of strontium oxide and strontium carbonate on the surface has been previously investigated. It has been demonstrated that the presence of carbon dioxide enhances the kinetics of the segregation. In this study, the influence of the segregation and the effect of carbon dioxide on the electrochemical performance of the cathode are investigated.
Electrochemical impedance spectroscopy (EIS) was used to study cathode performance on cells of the configuration LSCF (La_1-xSr_xCo_0.2Fe_0.8O_3-δ)/ gadolinium-doped ceria (GDC) barrier layer/ yttria-stabilized zirconia (YSZ)/ porous LSM-YSZ counter electrode. The cells were tested in CO₂-free air and in the presence of CO₂ at the operational temperature range of 600-800°C.

Hydrogen molecules are dissociated into protons and electrons at the fuel electrode of proton-conducting ceramic fuel cells. The protons flow through the proton-conducting BaZrO₃ electrolyte to arrive at the air electrode, while the electrons flow through an external circuit where a load is connected. They react with oxygen molecules at the air electrode to generate water molecules. In this work, we investigated proton conductivity at BaZrO₃ (001) surface using density functional theory and space charge model. Among the three low indexed (001), (011), and (111) surfaces, the BaO-terminated (001) surface was chosen by considering the surface energy as functions of barium chemical potential and partial oxygen pressure. The proton was segregated at the surface with segregation energies of -0.96 eV and it migrated from the surface to the subsurface with an energy barrier of 1.23 eV. Based on the proton conductivity obtained from these values, we found that the surface significantly impede the proton conduction.

Double perovskite structure material, GdBaCo₂O_5+δ (GBCO), has shown considerable promise as a candidate cathode for the development of intermediate temperature solid oxide fuel cells. The anisotropic crystal structure of GBCO is believed to contain oxygen vacancies ordered in the Gd plane. Depending upon the oxygen non-stoichiometry, δ = 0, 0.5 or 1, the Gd-plane could respectively be completely vacant, half filled or completely filled with oxygen. Ordered oxygen vacancies in one plane thus provide a direct channel for oxygen diffusion leading to higher values of oxygen chemical diffusion coefficient. In this study molecular dynamics calculations have been carried out to illustrate the effect of oxygen vacancy concentration in GBCO on oxygen diffusivity. Simulated oxygen diffusion in GBCO with variations in nonstoichiometry (δ = 0, 0.5, and 1) indicates that the diffusivity follows the trend, 0.5 > 1 > 0 at various temperature in the range 1000 - 1600 K. To elucidate the effect of doping Co with Fe in GBCO, oxygen diffusivity was simulated in 50% Co substituted systems. Here too the diffusivity follows the same trend: 0.5 > 0.

Ceria is a key material for applications in catalysis, solid oxide fuel cells and oxygen membranes. Depending on the operation conditions (i.e. temperature and oxygen partial pressure), dopant concentration and microstructure (e.g. nanocrystalline vs. microcrystalline), the overall ionic transport properties of ceria are limited either by the blocking behavior of the grain boundaries or by the local atomic disorder in the bulk (grain interior). In this contribution, the results of a series of conductivity measurements (electrochemical impedance spectroscopy) as well as microstructural analyses (XRD, XANES, EXAFS) are presented, which were performed on nanocrystalline and microcrystalline ceria doped with samarium, erbium and ytterbium with concentrations ranging between 10 and 30 at.%.
The main outcomes, which shed light on the correlation between local order and the oxygen ion transport properties, can be summarized as follows: (i) The nanocrystalline samples exhibit systematically lower bulk conductivities than the microcrystalline counterparts while (ii) the grain boundaries of the nanocrystalline specimens are proportionally less blocking than those of the microcrystalline ceramics. (iii) EXAFS data indicate that in samarium doped ceria (which is the composition exhibiting the largest conductivity) oxygen vacancies result to be located far from the dopant and close to Ce cations, whilst the opposite is observed for the compositions containing erbium and ytterbium. Finally, (iv) the combined analysis of EXAFS and conductivity data reveals that the disorder associated with cation-cation second shell correlates very well with the activation energies, meaning that the activation energy increases with increasing disorder.

Thin film devices with electrochemical function have attracted recent attention for sensors, fuel cells and related technologies. In the case of epitaxial films, the physical constraints introduced by the substrate may modify the behavior of the active oxide through chemical expansion. Pr-doped CeO₂ (PCO) films of 100, 110 and 111 orientation, prepared using pulsed laser deposition on zirconia and sapphire single crystal wafers, were studied as model systems. The approaches needed to accurately control the oxygen partial pressure from 1 to 10^-5 atm during discontinuous step changes were developed and the rate of change of oxygen partial pressure at the sample position measured. Both temperature-controlled isobaric and isothermal measurements at varied pO₂ were conducted at temperatures up to 800C. Step changes in the oxygen pressure at fixed temperatures were used to track the oxygen exchange coefficient with comparisons made between results obtained from strain measurements from substrate curvature and bulk dilatometry. The films show strong out-of-plane strain responses as a result of chemical expansion, which vary with film orientation and thermal history. Films on sapphire substrates show excellent stability and reproducibility when cycling to temperature and oxygen pressure extremes for as many as 6 cycles. The oxygen exchange coefficient is calculated by fitting the XRD-derived strain relaxation vs. time for small incremental changes in pO₂ at several temperatures. Differences between the thin film and bulk values are considered for the XRD and substrate curvature in the context of the film stress-free temperatures and thermodynamic models developed for bulk PCO.

An improved fundamental understanding of oxygen nonstoichiometry and oxygen surface exchange kinetics in oxide materials is essential for improving the performance of solid oxide fuel cells (SOFCs), permeation membranes, and oxygen storage materials used in emission catalysts. The ability to diagnose a material&’s behavior is therefore of importance, especially under operating conditions, such as elevated temperatures and reducing/oxidizing atmosphere. Even though oxide thin films are studied as model systems due to well-defined properties and reproducibility, conventional characterization methods often exhibit limitations. For example, electrical relaxation and electrochemical impedance spectroscopy (EIS) measurements for investigation of oxygen exchange kinetics can be influenced by the presence of metal contacts, while thermogravimetric analysis (TGA) is limited by mass sensitivity limitations.
We previously successfully introduced a novel experimental apparatus enabling the simultaneous measurement of optical absorption and electrode impedance of thin films under in-situ operating conditions. Non-contact optical absorption measurements were used for in situ recording of transient redox kinetics as well as the equilibrium Pr oxidation state and, in turn, the oxygen nonstoichiometry of Pr_0.1Ce_0.9O_2-δ (PCO) thin films under varying conditions of pO₂ and temperature. The oxygen nonstoichiometry of dense oxide thin films was also examined in situ by analyzing the chemical capacitance obtained from EIS measurements. The results of these measurements are examined in light of possible changes in defect thermodynamics between bulk and thin film PCO and the influence of different metal contacts on surface reaction kinetics.

CeO₂ and Y₂O₃-stabilized zirconia (YSZ) are two typical candidates for electrolyte materials in solid oxide fuel cells attributed to their high ion conductivities. Theoretical calculations indicate that the oxygen vacancy formation energy is considerably reduced at interfaces and oxygen vacancies expected to segregate to the interfaces might provide highways for rapid ion conduction [1]. The aim of our work is to obtain insights into the structure and chemistry of interfaces between CeO₂ and YSZ by scanning transmission electron microscopy (STEM) combined with electron energy-loss spectroscopy (EELS).
Epitaxial CeO₂ films were grown on YSZ (111) substrates using pulsed laser deposition. The CeO₂ film is approximately 30 nm thick and continuous, where the CeO₂ film and YSZ substrate have a cubic on cubic orientation relationship ((111) <1-10>_CeO2 // (111) <1-10>_YSZ). No reaction layers or other phases were identified at the interface. Periodical misfit dislocations were observed at the interface with extra atomic planes appearing in YSZ.
EELS line scans and atomic column-resolved EELS spectrum images across the CeO₂/YSZ interface were acquired, where the extracted EELS spectra illustrate the change of Ce-M_4,5 edge from the bulk to the interface. It is well known that the Ce-M_4,5 edges are valence sensitive. Since the possible presence of Ce³⁺ is seen as evidence of oxygen vacancy formation, oxidation states of cerium ions near the interface were investigated by EELS for which the intensity ratios of the Ce-M_4,5 white lines were analyzed. Measured spectra were compared with known reference spectra acquired from compounds containing Ce³⁺ or Ce⁴⁺. In addition, quantitative analysis has been performed on the Ce-M_4,5 edges via non-linear least squares fitting to study the ratio of Ce³⁺ to Ce⁴⁺ as function of the distance from the interfaces. It is revealed that most of the Ce ions were reduced from Ce⁴⁺ to Ce³⁺ at the interface region with a decay of several nanometers. Several possibilities of charge compensations are discussed. Irrespective of the details, such local non-stoichiometries are crucial not only for understanding charge transport in such hetero-structures, but also for understanding ceria catalytic properties [2].
References
[1] Fronzi et al., Phys. Rev. B 86 (2012) 085407
[2] Song et al., APL Materials 2 (2014) 032104
Acknowledgements
The authors acknowledge funding from the PhD student exchange program between the Max Planck Society and the Chinese Academy of Sciences and the Natural Sciences Foundation of China (Grant No. 51221264). The research leading to these results has received funding from the European Union Seventh Framework Program [FP/2007-2013] under grant agreement no 312483 (ESTEEM2). Financial support for the ARM200CF project by the Max Planck Society is gratefully acknowledged

The promise of direct and efficient conversion of chemical to electrical energy makes fuel cell development an area of great technological interest. Solid Oxide Fuel Cells (SOFCs) are one of the most promising technologies to meet this goal. However, current SOFCs operate at temperatures above 700^oC. This high temperature increases costs and decreases cell lifetime. To overcome this challenge we must develop materials that demonstrate high electrocatalytic activity and facile ion and electron transport at lower temperatures. A significant barrier to progress is a lack of experimental techniques that can probe the properties of these materials at high temperature in both oxidizing and reducing gas environments.
Neutron diffraction is one technique that can achieve this goal to reveal information relating to phase transition, order-disorder phenomenon, and the presence of anionic and cationic vacancies in crystalline oxides. Most powerfully, all of this information is collected in a single experiment over a wide variety of operating conditions. Analysis of these results enables visualization of diffusion pathways in ionic conductors, guiding future material development. This presentation will discuss results from a recently developed in-situ neutron diffraction cell developed for the POWGEN beamline at the Spallation Neutron Source, Oak Ridge National Laboratory.
The results for these studies will be utilized to interpret the surface oxygen exchange kinetics and electrochemical performance for a variety of materials to demonstrate the impact of this technique.

The microscopic structural and morphological properties of oxygen ion and proton conducting oxides can strongly affect their total electrical conductivity. According to recent literature, tensile or compressive lattice distortions of the conductor modify the potential barrier for the migration of the charge carriers. This effect is indeed particularly important since significantly larger conductivities may be achieved at lower temperatures.
Several experimental measurements performed on oxygen ion conducting thin films show that a tensile lattice strain, induced in the direction of the migration of the charge carriers, reduces the activation energy for charge transport, while the opposite effect has been observed in the case of a compressive stress. However, the literature is still rather controversial since also tensile stressed films showing no evidence of strain effects on their conducting properties have been reported, as well as enhanced conductivities resulting from a compressive stress of the conductor.
Concerning proton conducting oxides, the effect of the stress-induced lattice distortions on the protonic conductivity has been addressed only in very few studies. Significantly larger activation energies were measured as a result of a compressive stress, while no measurement has been reported so far on the effect of a tensile strain.
Thin film deposition technology is a powerful tool for the fabrication of model samples to investigate these effects. However, the unambiguous identification of the stress state of the conductor is often an issue, and the impact of the thin film growth process on the resulting strain is not yet fully understood.
For this study, multi-beam optical stress sensor and reflection high energy electron diffraction have been coupled for the first time to probe in-situ the growth mode and the mechanisms of stress generation and evolution in thin oxide films grown by pulsed laser deposition. Thin films of yttria-stabilized zirconia, Sm-doped CeO₂, and Y-doped BaZrO₃ have been investigated. Different and tunable stress states, as well as fully relaxed crystalline structures can be identified in-situ under different deposition parameters, using different substrates or suitable buffer layers.
This will help to unveil the microstructural properties that lower the potential barrier for charge transfer and to identify the general guidelines to engineer innovative and highly performing materials.

The operation temperature of electrochemical devices for energy conversion, such as Solid Oxide Fuel Cells (SOFCs), can be lowered by decreasing the electrolyte thickness or by using a fast low temperature ionic conductor [1].
Bismuth oxide based materials, which has the highest oxygen ion conductivities, attracted great interest as a possible electrolyte for SOFC [1-2]. However, owing to the inherent instability of these materials at lower temperature and oxygen partial pressures, these materials have found limited use [3, 4]. Here we show the structural and electrical properties of erbium oxide stabilized bismuth oxide (Er_0.4Bi_1.6O_3-δ) thin films deposited by Pulsed Laser Deposition onto different single crystals, i.e. MgO (100), Al₂O₃ (1000) and SrTiO₃ (100). The orientation and the microstructure of the as-grown films found to be dependent on the type of substrate and growth conditions. Detailed investigation of the materials stability revealed that that the films are unstable already under the electrical bias, showing remarkable changes in the crystalline orientation, microstructure and chemical composition.
[1] E. D.Wachsman, K. T. Lee, Science, 334 (2011) 935-939.
[2] P. Shuk, H.D. Wiemh, U. Guth, W. Göpel, M. Greenblatt, Solid State Ionics, 89 (1996) 179-196.
[3] T. Takahashi, T. Esaka, H. Iwahara, J. Appl. Electrochem., 7 (1977) 299-302.
[4] S. Boyapati, E. D. Wachsman, N. Jiang, Solid State Ionics, 140 (2001) 149-160.

Perovskite-type yttrium-doped barium zirconate (BaZr_1-xY_xO_3-δ, or BZY) is one of the most promising oxide proton conducting electrolytes because BZY offers high proton conductivity as well as fairly high thermodynamic stability. Yttrium ions in BZY, on one hand, provide oxygen vacancies to which protons are to be incorporated, but, on the other hand, act as traps and impede the proton transport because the trivalent yttrium ions are more negatively charged than the tetravalent zirconium ions. If the yttrium content is more dominant than the zirconium content, more than half of the oxygen ions are neighboring with the yttrium ions and thus the proton transport path can be created with yttrium-neighbored oxygen ions only. In such a situation, trapping effect may be suppressed and the proton conductivity has the potential to increase with increasing yttrium concentration. However, the proton conducting behavior at high yttrium concentration (x > 0.25) has not been reported so far because, at high yttrium content, yttrium-rich secondary phases precipitate and it is difficult to create BZY with high yttrium concentration.
Here we report formation of BaZr_1-xY_xO_3-δ epitaxial thin films with high yttrium concentrations (x = 0 - 0.5) grown by radio-frequency (RF) magnetron sputtering on MgO (100) and (110) substrates. For all the compositions (x = 0 - 0.5), single phase perovskite-type structures of BZY were successfully obtained. Lattice constants monotonically increased with yttrium concentrations obeying Vegard&’s law. This indicates that yttrium ions occupy zirconium sites, not barium sites, as the relationship of the ionic radii of constituent ions is r_Ba2+ > r_Y3+ > r_Zr4+. The measured compositions of BZY were Ba_0.995Zr_0.905Y_0.102O_3-δ (nominally x = 0.1), Ba_1.024Zr_0.662Y_0.314O_3-δ (nominally x = 0.3), and Ba_0.991Zr_0.523Y_0.486O_3-δ (nominally x = 0.5), revealing that all the materials are almost at the stoichiometric compositions. XRD analysis indicated that the symmetry of the BZY epitaxial thin films with x = 0, 0.3, and 0.5 are tetragonal P4mm type, indicating no symmetry reduction even at x = 0.5 due presumably to epitaxial stabilization of the lattices. We observed increase in oxygen compositions after annealing the BZY films under moisted Ar atmosphere, which verifies that protons were incorporated in the BZY films.
These epitaxial BZY thin films with high yttrium concentrations have the potential to show higher proton conductivity than previously reported BZY materials. The study of the proton conductivity is currently under way.

Yttrium-doped barium zirconate, BaZr_1-xY_xO_3-δ (BZYx), has been investigated due to its relatively high proton conductivity at intermediate temperatures and chemical stability in carbon dioxide rich atmospheres [1]. These characteristics make this material suitable to be applied as solid electrolyte in solid oxide fuel cells despite of its poor sinterability drawback. Recently, BZYx defect chemistry has been studied intensively because it plays an important role in understanding the proton conductivity [2]. In this work, the enthalpy of formation of barium zirconate and Ba(Zr_1-xY_x)O_3-δ, (x = 0.1 -0.5) solid solutions were determined to investigate the thermochemistry involved in phase formation with increasing dopant content [3]. The BZYx powders were synthesized by an oxidant-peroxo method, and heat treated at 1200 ^oC for 24 h [4]. The samples chemical composition was determined by electron microprobe and its crystalline phase was characterized by X-ray diffraction and Raman spectroscopy. The enthalpy of formation from binary oxides were calculated from high-temperature oxide melt solution calorimetry measurements performed with molten 3Na₂Omiddot;4MoO₃ solvent at 702 ^oC. The BZYx solid solutions were single cubic perovskite phases, but with increasing Y content, some Ba loss occurred. The enthalpy of formation from binary oxides is exothermic for all the compositions and becomes less negative when yttrium content increases, with a value of -115.12 ± 3.69 kJ/mol for x = 0 and -77.09 ± 4.31 kJ/mol for x = 0.5. The destabilization is attributed to the lower basicity of Y₂O₃ than of BaO, lattice strains and oxygen vacancy formation caused due to doping. The increase of the exothermic contribution above x = 0.3 might be related with the influence of vacancy clustering formation or the consumption of oxygen vacancies. The thermochemical data are consistent with the observed trends in proton conductivity where it increases up to 20 mol% of Y substitution and then decreases for higher dopant contents.
We gratefully acknowledge FAPESP for financial support (Proc.2011/50197-0 and 2013/10928-0).
References
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