Nickel–cobalt oxides supported on Co/N decorated graphene as an excellent bifunctional oxygen catalyst

Abstract

The design of highly efficient electrocatalysts for the oxygen evolution reaction (OER) and oxygen reduction reaction (ORR) plays a key role in the development of various renewable energy storage and conversion devices. Recently, metal–organic framework (MOF) derived materials have shown great potential in ORR and OER; however, they may suffer from poor conductivity with limited electrochemical performance especially towards OER. In this work, nickel–cobalt oxides supported on Co/N decorated graphene were prepared by introducing nickel in a zeolitic imidazolate framework-67 (ZIF-67) as the precursor, which showed improved OER performance due to the as-derived Ni_xCo_yO₄, and maintained the ORR performance of Co/N doped carbon at the same time. Meanwhile, graphene was utilized to further enhance the electrochemical surface area and charge transfer efficiency. The resulting composites show a potential of 0.796 V at 3 mA cm⁻² and superior stability to Pt/C towards ORR, as well as a potential of 1.629 V to achieve 10 mA cm⁻² current density for OER, which is much better than that of IrO₂. In all, the overvoltage between ORR and OER was just 0.833 V, demonstrating the great potential of the composite in metal–air batteries as a bifunctional oxygen catalyst.