Catalytic Roles of Perovskite Oxides in Electrochemical Oxygen Reactions in Alkaline Media

We investigated the catalytic activities of three perovskite oxide (LaMnO 3 , La 0.8 Sr 0.2 MnO 3 , and La 0.8 Sr 0.2 CoO 3 ) thin films grown by pulsed laser deposition when they were used as oxygen electrodes for aqueous rechargeable metal-air batteries. The oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) on perovskite oxide thin films in alkaline solution were observed by linear sweep voltammetry using a rotating disk electrode. Although we confirmed that the resultant perovskite oxide thin films were sufficiently electroconductive to facilitate the ferricyanide reduction reaction on themselves, the ORR activities of perovskite oxide thin films were much lower than those of conventional composite electrodes, which consist of perovskite oxide powder and carbon black. In contrast, the OER activities of thin films and their activity order (La 0.8 Sr 0.2 CoO 3 > LaMnO 3 ≥ La 0.8 Sr 0.2 MnO 3 ) were almost the same as those of conventional composite electrodes. We discuss the catalytic roles of perovskite oxides and carbon powder in oxygen electrodes and propose possible reaction paths for the ORR and OER.