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

Abstract

The effects of Co and Mo doping on the properties of SrFeO3-δ 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-δ and SrFe0.45Co0.45Mo0.1O3-δ phases. All compositions lose oxygen for temperatures ≥400–450 °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 °C. The increase of ionic radii with reduction of Fe/Co + IV species results in greater thermal expansion for T > 450 °C. Polarization resistance without bias lowers considerably on Co doping, from ~0.55 Ω cm2 for pure SrFeO3-δ, to ~0.2 Ω cm2 for SrFe0.45Co0.45Mo0.1O3-δ at 700 °C, but not on Mo doping (~0.5 Ω cm2). 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-δ with more moderate thermal expansion.