Origin of the initial polarization behavior of Sr-doped LaMnO3 for O2 reduction in solid oxide fuel cells

The initial behavior of O2 reduction reactions was studied on freshly-prepared Sr-doped LaMnO3 (LSM) electrodes with and without dilute acid etching at 900°C in air. LSM electrodes without acid etching showed very high polarization potential for the O2 reduction and the electrode performance improved significantly with the cathodic current passage. On the other hand, for the reaction on LSM electrode after acid etching, the change in the polarization potential with the current passage time was much smaller and cathodic current passage had little enhancing or activation effect on the electrode performance. The results indicate that the dilute acid etching effectively replaced the activation process of the cathodic polarization on LSM electrodes and the initially very high polarization losses for the reaction on LSM electrodes are most likely originated from the passivation species such as MnOx and in particular SrO species originally enriched on the LSM electrode surface.