Co3O4 nanoneedles grown on graphene oxide as an efficient electrocatalyst for hybrid water electrolysis through alternative anodic oxidation reactions

Co 3 O 4 nanoneedles have been incorporated onto the layers of graphene oxide (Co 3 O 4 NN/GO) through a simple hydrothermal route. The high energy input for water electrolysis can be reduced by hybrid water electrolysis via electrolyte engineering. In this study, oxygen evolution reaction (OER) has been replaced with oxidation of nitrogen containing compounds such as urea and hydrazine (UOR and HzOR). Among transition metal oxides, spinel Co 3 O 4 exhibits switchable redox states of Co 2+ and Co 3+ . Also, its electronic conductivity is improved with GO carbon support which make it a promising electrocatalyst towards OER as well as UOR and HzOR. In this study, the Co 3 O 4 NN/GO has delivered potentials of 1.56, 1.29, and 0.043 V vs RHE at 10 mA cm −2 for OER, UOR, and HzOR in alkaline medium, respectively. The two-electrode cell constructed by employing Co 3 O 4 NN/GO as anode and Pt/C as cathode required an ultra-low cell voltage of 0.33 V for overall hydrazine-assisted water electrolysis, which was 1.32 V lower than that of a conventional alkaline water electrolyzer (1.64 V). The cost-effectiveness and simple conversion of biomass orange peel to GO under mild conditions with the incorporation of Co 3 O 4 nanoneedles have provided a new route for catalytic design with carbon supports from biomass for highly energy-efficient hybrid water electrolysis.