Modeling current–voltage relationships of mixed conducting cathode materials for solid oxide fuel cells

Abstract

In recent decades, high-temperature oxygen reduction reaction on mixed conducting cathodes were investigated intensively by many researchers. Computational approaches as well as electrochemical and spectroscopic studies have been made to elucidate the kinetics. Contribution of oxygen vacancy to the reaction rate was suggested in multiple reports, and plausible reaction pathways were proposed based on density functional theory (DFT) calculations. The picture of oxygen reduction reaction has become clearer in these years. However, there still is a discussion about a credible formula that represents the current–voltage relationships. Discrepancies are found among the reported data on the magnitude of the rate constant and on its dependencies on partial pressure and temperature. The difference is significant between a model electrode and a practical porous electrode. Comparison of the results suggests the existence of series reaction barriers, that is, the surface reaction and subsurface transport, which should be considered for consistent representation of the total electrode process.