Cathode processes and materials for solid oxide fuel cells with proton conductors as electrolytes

This article provides a brief review of the cathode reaction mechanisms in proton-conducting solid oxide fuel cells (H-SOFCs) and a comparative analysis of electrochemical performance and the ionic and electronic transport in cathode materials. The transfer of protons from electrolyte to triple phase boundaries (TPBs) and the diffusion of O-ad(-) from catalytic sites to TPBs are proposed to be the rate-limiting steps for H-SOFCs, of which the latter is more related to the cathode components, microstructure, conducting species and electrical conductivity. The experimental and theoretical analyses also suggest that cathode materials with electron and proton conductivity present smaller polarisation resistances due to the ability of protons to transfer from the electrolyte into the bulk, which extends the reaction areas for protons and oxygen species to the entire gas/cathode surface.