The total measured overpotential of a porous SOFC electrode is governed by a complex mixture of rates, including heterogeneous catalysis, interfacial charge transfer, bulk and surface ion transport and gaseous diffusion. In order to better understand the role of microstructure in mediating these rates, our group has been developing detailed microkinetic models (based on finite-element analysis), which employ various 3D representations of the electrode microstructure. These 3D representations span a range of complexity, from pseudoparticles (such as rods or spheres) to solid meshes generated from 3D images of the microstructure (based on 3D FIB-SEM reconstructions). These models have been used to explore where and under what circumstances the fine details of the microstructure matter to performance, and where macrohomogeneous approximations can be made without loss of accuracy. We have used these models to aid interpretation of linear (EIS) and nonlinear (NLEIS) impedance response of single-phase porous mixed conducting SOFC cathodes.
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