Simulation of Surface-Potential Driven ORR Kinetics on SOFC Cathode with Parallel Reaction Pathways

In this research, the polarization behavior and kinetic pathways of an SOFC cathode have been investigated with a 1-D continuum model incorporating material physical properties and surface potential effects into a multi-step ORR kinetic formalism. It is found that (1) Two different types of 3PB-to-2PB pathway transitions can be identified. A strong 2PB pathway contribution leads to an explicit transition, while an implicit transition implies more favorable 3PB kinetics. The predicted kinetic trends qualitatively agree with literature results on single-phase LSM cathodes in different configurations and operation conditions; (2) The explanation for the different transition modes concerns the fact that the mass transport limitation of the 3PB path is more easily reached (at lower overpotential) when incorporation kinetics are favored by the material properties; and (3) The surface potential is found to strongly control the oxygen adsorption by introducing a rate-limit for cathodes with lower oxygen coverage, and can drive the incorporation faster under 3PB-favorable states. (C) 2014 The Electrochemical Society. All rights reserved.