Electrical and electrochemical properties of the Sr(Fe,Co,Mo)O3-δ system as air electrode for reversible solid oxide cells

The effects of Co and Mo doping on the properties of SrFeO3-delta perovskite as air electrode in reversible solid oxide cells have been analysed. The oxygen-ordered parent phase exhibits a high oxygen-vacancy content, which is partially reduced on doping, accompanied by stabilisation of cubic symmetry for SrFe0.9Mo0.1O3-delta and SrFe0.45Co0.45Mo0.1O3-delta phases. All compositions lose oxygen for temperatures >= 400-450 degrees C, with a concomitant decrease of electron-hole conductivity. Oxide-ionic conductivity determined by Faradic efficiency significantly improves for the Co-doped composition, reaching 0.026 S cm(-1) at 750 degrees C. The increase of ionic radii with reduction of Fe/Co + IV species results in greater thermal expansion for T > 450 degrees C. Polarization resistance without bias lowers considerably on Co doping, from similar to 0.55 Omega cm(2) for pure SrFeO3-delta, to similar to 0.2 Omega cm2 for SrFe0.45Co0.45Mo0.1O3-delta at 700 degrees C, but not on Mo doping (similar to 0.5 Omega cm(2)). However, under cathodic and anodic polarization, a comparable, excellent performance at 650 C of all compositions indicates their considerable promise as air electrodes for reversible solid oxide fuel cell-electrolyser systems, particularly for SrFe0.9Mo0.1O3-delta with more moderate thermal expansion.