Engineering Composite Oxide SOFC Anodes for Efficient Oxidation of Methane

Kim, Guntae; Corre, Gaël; Irvine, John T. S.; Vohs, John M.; Gorte, Raymond J.

doi:10.1149/1.2817809

Cited by 142 publications

(122 citation statements)

References 23 publications

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“…Our results are consistent with previous infiltrated electrode experimental work, which has reported the conductivity of infiltrated electrodes to be approximately 2% to 5% of the bulk conductivity. 5,6,16,22 …”

Section: Resultsmentioning

confidence: 99%

Insights into the Design of SOFC Infiltrated Electrodes with Optimized Active TPB Density via Mechanistic Modeling

Reszka

Snyder

Gross

2014

J. Electrochem. Soc.

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A mechanistic model for the prediction of total and active three phase boundary density (TPB), in combination with effective conductivity, of infiltrated solid oxide fuel cell (SOFC) electrodes is presented. Varied porosities, scaffold:infiltrate size ratios, and pore:infiltrate size ratios were considered, each as a function of infiltrate loading. The results are presented in dimensionless form to allow for the calculation of any infiltrate particle size. The model output compares favorably to the available experimental result. The results show that the scaffold:infiltrate size ratio has the greatest impact on the TPB density, followed by the porosity and then the pore:infiltrate size ratio. The TPB density is shown to monotonically decrease with increasing scaffold:infiltrate and pore:infiltrate size ratios; however, it shows a maximum with respect to porosity. Each of these results are explained by examining the interfacial areas of each of the three phases as a function of the infiltrate loading. The model provides insight toward the rational design of infiltrated electrodes. Infiltrated solid oxide fuel cell (SOFC) electrodes offer numerous advantages over conventional co-sintered electrodes. First, a broader choice of electrode materials is possible because materials that melt or chemically react with the electrolyte at conventional sintering temperatures can be considered.1-6 Second, a higher three-phase boundary (TPB) density can be achieved, which is attributed to the smaller particle sizes.2,3,7-9 These two advantages result from a lower processing temperature of the infiltrated phase compared to conventional sintering temperatures required of co-sintered electrodes.Three additional advantages of infiltrated electrodes are associated with the unique morphology created by coating the surface of a presintered porous scaffolding with an infiltrated phase. The first morphological advantage is a mitigation of the coefficient of thermal expansion (CTE) mismatch between the electrolyte and the electrode. 10,11The second advantage is a stabilization of the electrode mechanical properties during redox cycling, 5,12 Finally, less material is needed to form an interconnected network of the infiltrated phase throughout the electrode. 6,10,[12][13][14][15] Although the benefits of infiltrated electrodes have been clearly demonstrated experimentally, researchers suggest that the electrode designs are not optimized. 3,5,6,14,16 This is understandable because it is laborious to consider all of the combinations and permutations of the sizes and shapes of infiltrate particles, scaffold particles, and pores as well as the wide range of possible porosities. In order to more effectively and efficiently design electrodes, several computational models have been recently reported. Zhang et al. utilized a particle-layer model to estimate the TPB density, effective thickness of the electrochemically active region, and polarization resistance of cathodes.9 A more recent report by Zhang et al. utilized a numerically generated thr...

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Section: Resultsmentioning

confidence: 99%

Insights into the Design of SOFC Infiltrated Electrodes with Optimized Active TPB Density via Mechanistic Modeling

Reszka

Snyder

Gross

2014

J. Electrochem. Soc.

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“…In parallel, it has become evident that addition of metal nanoparticles to either oxide or composite (ceramic and metal, cermet) anodes can substantially enhance catalytic activity. Most such studies again address hydrocarbon utilization, [10][11][12][13] but enhancements are oen observed even for hydrogen electro-oxidation.…”

Section: 9mentioning

confidence: 99%

Robust nanostructures with exceptionally high electrochemical reaction activity for high temperature fuel cell electrodes

Jung

Choi

et al. 2014

Energy Environ. Sci.

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Metal nanoparticles are of significant importance for chemical and electrochemical transformations due to their high surface-to-volume ratio and possible unique catalytic properties. However, the poor thermal stability of nano-sized particles typically limits their use to low temperature conditions (<500 C).Furthermore, for electrocatalytic applications they must be placed in simultaneous contact with percolating ionic and electronic current transport pathways. Broader contextSolid oxide fuel cells (SOFCs) provide unparalleled fuel-to-electric conversion efficiency across power scales, from a few milliwatts to hundreds of megawatts. A key barrier to widespread SOFC deployment has been high cost, in part attributable to the high temperature of operation, typically in the 800-1000 C range.Lower temperature operation, in turn, has been hindered by poor electrocatalysis rates. Here we demonstrate SOFC anodes with unprecedented activity for both hydrogen and methane electro-oxidation at 600 C. The innovation lies in the use of nanostructured ceria in combination with ultra-low loadings (11 mg cm À2 ) of catalytic metals: Pt, Pd, Ni or Co. Despite the nanoscale features, the activity experiences negligible degradation over a continuous measurement period of 120 h. This work sets the stage for the adoption of high efficiency SOFCs for the cost-effective utilization of natural gas in electric power generation.

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“…For example, the tortuosity can be estimated from four probe conductivity measurements on porous slabs. 66 The resulting tortuosity value arises from the network of interconnected YSZ fins (the contribution from dead-end fins is not explicitly accounted for). For straight YSZ fins shown in Figs.…”

Section: Steady-state Modelmentioning

confidence: 99%

Modeling Impedance Response of SOFC Cathodes Prepared by Infiltration

Bidrawn

Vohs

Gorte

2011

J. Electrochem. Soc.

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A mathematical model has been developed to understand the performance of electrodes prepared by infiltration of La 0.8 Sr 0.2 FeO 3 (LSF) and La 0.8 Sr 0.2 MnO 3 (LSM) into yttria-stabilized zirconia (YSZ). The model calculates the resistances for the case where perovskite-coated, YSZ fins extend from the electrolyte. Two rate-limiting cases are considered: oxygen ion diffusion through the perovskite film or reactive adsorption of O 2 at the perovskite surface. Adsorption is treated as a reaction between gas-phase O 2 and oxygen vacancies, using equilibrium data. With the exception of the sticking probability, all parameters in the model are experimentally determined. Resistances and capacitances are calculated for LSF-YSZ and there is good agreement with experimental values at 973 K, assuming adsorption is rate limiting, with a sticking probability between 10 À3 and 10 À4 on vacancy sites. According to the model, perovskite ionic conductivity does not limit performance so long as it is above $10 À7 S/cm. However, the structure of the YSZ scaffold, the ionic conductivity of the scaffold, and the slope of the perovskite redox isotherm significantly impact electrode impedance. Finally, it is shown that characteristic frequencies of the electrode cannot be used to distinguish when diffusion or adsorption is rate-limiting.

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Engineering Composite Oxide SOFC Anodes for Efficient Oxidation of Methane

Cited by 142 publications

References 23 publications

Insights into the Design of SOFC Infiltrated Electrodes with Optimized Active TPB Density via Mechanistic Modeling

Insights into the Design of SOFC Infiltrated Electrodes with Optimized Active TPB Density via Mechanistic Modeling

Robust nanostructures with exceptionally high electrochemical reaction activity for high temperature fuel cell electrodes

Modeling Impedance Response of SOFC Cathodes Prepared by Infiltration

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