Transient 3D FEM Impedance-Model for Mixed Conducting Cathodes

The performance of solid oxide fuel cells (SOFCs) is often determined by the polarization resistance of the electrodes. Electrochemical impedance spectroscopy (EIS) enables a deconvolution of individual electrochemical processes. In case of mixed ionic-electronic conducting (MIEC-) cathodes the impedance spectra result from the coupling of gas diffusion, surface exchange and bulk diffusion of oxygen ions. In this paper we present a three-dimensional (3D) finite element method (FEM) model which allows the transient simulation of the underlying processes in a porous cathode structure. The developed model is validated with a well established homogenized 1D model by comparing the area specific resistance and the corresponding impedance spectra. In case of a homogeneous 3D microstructure the FEM simulation results show an excellent agreement with the homogenized 1D model. Furthermore, the 3D FEM model is applied for impedance simulations of a technical MIEC cathode which microstructure was reconstructed from FIB tomography.