Theoretical modeling of air electrode operating in SOFC mode and SOEC mode: The effects of microstructure and thickness

•Micro electrode modeling for solid oxide electrochemical cells.•Effects of microstructure and thickness on SOFC are larger than that on SOFC.•Effects of opposite directions of O2 diffusion.•Difference between air electrodes for SOFC and SOEC.

A theoretical model of solid oxide cells coupled with heterogeneous elementary reactions, electrochemical reactions, electrode microstructure and mass and charge transport is developed and validated. The effects of microstructure, thickness and temperature of air electrode on the cell performance in both solid oxide electrolysis cell (SOEC) and solid oxide fuel cell (SOFC) are individually discussed. The simulation results indicate that the growth in the thickness of air electrode reduces the effect of particle diameter while dramatically enlarges the effect of porosity. The microstructure and thickness of air electrode and temperature have significantly different impacts on solid oxide cells operating in SOEC mode and SOFC mode. The results indicate that the optimizing strategy of air electrode for SOEC and SOFC should be different especially for a thicker air electrode. The proposed model can be a useful tool for bridging the electrode geometry and microstructure design and optimization.