Selection and study of basic layered cobaltites as mixed ionic–electronic conductors for proton conducting fuel cells

•Several cobaltites of different structure types have been studied as possible MPEC.•REBaCo2O5 + δ oxygen vacancy ordered perovskite is the most stable in wet air.•The chemical compatibility of these materials with the BaZr0.9Y0.1O3 electrolyte is good.•Water insertion is observed in the REBaCo2O5 + δ series, presumably as OHO• proton defects.

High Temperature Steam Electrolysis using Proton Conducting Cells is a promising method for large-scale hydrogen production, but such system requires the development of new electrode materials ideally presenting Mixed Proton and Electron Conductivity. Different cobaltites were investigated in terms of durability and compatibility with the BaZr0.9Y0.1O3 proton conducting electrolyte. REBaCo2O5+δ (RE = Pr, Nd, Sm, Gd, Y), YBaCo4O7, Ca3Co4O9 and Ca3Co2O6, were considered, among which the vacancy ordered perovskites were found to be the most stable in wet air. Oxygen vacancy formation and hydration properties of REBaCo2O5+δ were studied by iodometry and TGA in dry and wet atmospheres, respectively.