Oxygen reduction/evolution activity of air electrodes using nitrogen-doped and perovskite-type oxide-loaded reduced graphene oxides

Oxygen reduction/evolution bi-functional air electrodes with high activity are required for constructing high-performance metal–air secondary batteries. Conventionally, carbon-supported electrocatalysts have been used as the air electrode materials. However, these types of air electrodes have a problem that the carbon black is corroded to water-soluble organic compounds during oxygen evolution reaction. Therefore, we have investigated reduced graphene oxides as an alternative to the conventional carbon black. Cyclic voltammetry in the range of the potential in which the oxygen evolution reaction occurs revealed that the reduced graphene oxide is stable against corrosion during the oxygen evolution reaction. This result indicates that the reduced graphene oxide is a promising candidate electrode material for bi-functional air electrodes. To improve the oxygen reduction and evolution activities of reduced graphene oxides, doping of nitrogen species and loading of perovskite-type oxide catalysts to reduced graphene oxide were examined. It was found that doping of nitrogen species was effective for improving both the oxygen reduction and evolution activity. LaMnO3 and LaNiO3 catalysts were effective for improving the oxygen reduction and evolution activities, respectively. The best oxygen reduction and evolution activity was obtained by the LaMnO3-loaded nitrogen-doped reduced graphene oxide and LaNiO3-loaded nitrogen-doped reduced graphene oxide, respectively.