High surface electron-proton mixed conduction at medium temperature of c-axis oriented BaCe_0.7Ru_0.1Y_0.2O_{3−<i>δ</i>} thin film

Abstract Electrochemical reaction-based solid oxide fuel cells (SOFCs), which operate at a medium temperature range from 300 to 600 °C, are expected to be a new renewable energy source. The performance of their electrochemical reactions for SOFC anode and cathode electrode membranes can be enhanced using electron-ion mixed conductor material. To realize a practical anode electrode film for SOFCs, c -axis oriented BaCe 0.7 Ru 0.1 Y 0.2 O 3− δ (BCRY) thin films were prepared on an MgO (100) substrate by RF magnetron sputtering. The oxygen vacancy concentration in the BCRY thin films was quantitatively evaluated by X-ray absorption spectroscopy and defect chemical analysis. Proton conductivity was proven from the O 1 s photoemission spectrum showing an OH - peak formed on the oxygen ion sites. Electron conductivity was proven from the small density-of-state at the Fermi level ( E F ) and the energy difference between the top of the valence band and the E F , which is close to the activation energy of the conductivity. The wet-annealed BCRY thin film, which exhibits surface electron-proton mixed conductivity of more than ∼10 −3 S cm −1 at 300 °C, can be applied as a practical anode electrode film for SOFC operating in the medium temperature range.