Multi-Physics Simulation of SOFC Button Cell with Multi-Step Charge Transfer Model in Composite LSM/YSZ Cathode

Abstract

In the present study, numerical simulation of a solid oxide fuel cell (SOFC) button cell with a multi-step oxygen reduction reaction (ORR) mechanism in a composite cathode was developed for better understanding of processes within the SOFC. The ORR mechanism involves both surface charge transfer through triple phase boundary (3PB) and bulk charge transfer via a two phase boundary (2PB) pathway. The developed multi-physics simulation considered the charge conservation and species transportation through porous media. The developed simulation was first applied to a dense thin film study only involving surface adsorption and the 2PB pathway. By calibrating the simulation with measurements of dense thin film cathodes, the kinetic rates of rate-determining steps in ORR model were decided. Finally, the simulations of full SOFC button cell were calibrated with measured cell performance (polarization curves and impedance behavior) at three different air/fuel utilization conditions. It was found that it is beneficial to determine the kinetic rates of rate-determining steps in a multi-step charge transfer model before calibrating the simulations for full cell system. With the determined rates, the various performance of different cells can be attributed to the microstructure versus material variations. Therefore, the present study not only helps better understand the details of processes in SOFC but also provides guidance for electrode design and manufacturing.