A study of synergistic effect on oxygen reduction activity and capacitive performance of NiCo2O4/rGO hybrid catalyst for rechargeable metal-air batteries and supercapacitor applications

An effective non-precious bare NiCo2O4 (NCO) micro-shrubs and graphene (rGO) supported hybrid catalysts (NCO/rGO) were prepared by a simple urea assisted one-pot hydrothermal route. The authors were motivated to investigate an influence of synergistic effect between NCO nanoparticles and rGO sheets of freshly prepared hybrid catalysts (NCO/rGO) by adjusting the starting metal (nickel & cobalt nitrate hexahydrate) precursors, which has been denoted as 50 NCO/rGO, 100 NCO/rGO & 150 NCO/rGO in the present work. All the freshly prepared rGO, NCO and rGO supported hybrid catalysts with three different NCO mass loading samples were characterized through different characterization techniques such as XRD, FT-Raman, HR-SEM, HR-TEM, LSV, CV and galvanostatic charge/discharge studies, respectively. Among them, the rGO supported hybrid catalyst with lower amount of NCO mass loading (50 NCO/rGO) exhibits an outstanding oxygen reduction reaction (ORR) activity with lower onset potential, high limiting current density via. four-electron mechanism in an O-2-saturated 0.1 M KOH electrolyte solution at room temperature. In addition, the specific capacitance of hybrid electrode is found to be 1305 F g(-1) at a scan rate of 5 mV s(-1) with 89% retention of cyclic stability even after 3000 cycles. The observed electrocatalytic activity and capacitive performances of an optimized hybrid sample (50 NCO/rGO) is strongly indicates an influence of better synergistic effect between NCO nanoparticles and rGO nanosheets. Hence, an optimized rGO supported hybrid catalyst (50 NCO/rGO) could be a promising electrocatalyst as well as hybrid electrode for metal-air batteries and supercapacitor applications, respectively.