Oxygen reduction mechanism at Ba0.5Sr0.5Co0.8Fe0.2O3-δ cathode for solid oxide fuel cell

Perovskite structure Ba0.5Sr0.5Co0.8Fe0.2O3-delta (BSCF) and La0.9Sr0.1Ga0.8Mg0.2O3-delta (LSGM) powders have been successfully synthesized by glycine-nitrate combustion process. A porous and crack-free BSCF cathode is obtained by spraying the slurry of BSCF powders and terpineol onto LSGM pellet. The oxygen reduction reaction mechanism has been investigated by AC impedance spectroscopy and cyclic voltarnmetry method. AC impedance spectroscopy analysis shows that there are two different processes in the cathode reaction which are related to oxygen dissociation/adsorption and bulk oxygen diffusion. And the molecular oxygen is involved in the rate-determining step. The polarization resistance decreases with an increase of temperature and the oxygen partial pressure. With an increase of the applied DC bias, the logarithm of the polarization resistance decreases linearly due to additional oxygen vacancies and the lowered chemical potential of oxygen at the BSCF/LSGM interface by the applied voltage. The exchange current density reaches to 182 mA cm(-2) at 700 degrees C, suggesting that the ORR kinetics at the BSCF/LSGM interface is high due to the excellent mixed ionic and electronic conductivity of BSCF. (C) 2008 International Association for Hydrogen Energy. Published by Elsevier Ltd. All rights reserved.