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

Abstract

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...

Developing a Coupled Statistical and Monte Carlo Approach for Geometric Modeling and Optimizing of Infiltrated Solid Oxide Fuel Cell Electrode

“…A mechanistic model to predict the active TPB density, in combination with effective conductivity of infiltrated SOFC electrodes is presented by Reszka et al. . Recently Kishimoto et al.…”

Investigation of the geometric property hull for infiltrated solid oxide fuel cell electrodes

“…In that study, they present a methodology to relate an experimentally observed degradation in the effective electronic conductivity of infiltrated electrodes to a reduction in active TPB length as a function of time. A mechanistic model to predict the active TPB density, in combination with effective conductivity of infiltrated SOFC electrodes, is presented by Reszka et al Their study showed that the scaffold/infiltrate size ratio has the greatest impact on the TPB density, followed by the porosity and pore/infiltrate size ratio. Their model provided an insight over the rational design of infiltrated electrodes and conforms well to experiment.…”

Preserving Nanomorphology in YSZ Scaffolds at High Temperatures via In Situ Carbon Templating of Hybrid Materials

“…In doing so, performance degradation rates and cost would both decrease substantially. A key factor in improving low‐temperature SOFC performance is to increase the density of electrochemically active sites in the porous ceramic electrode composites …”

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