Time-dependent oxidation of graphite and cobalt oxide nanoparticles as electrocatalysts for the oxygen evolution reaction

Water splitting is a promising way of producing hydrogen, but a highly efficient and durable electrocatalyst to accelerate the oxygen evolution reaction (OER) is required. In this study, we report cobalt oxide (Co3O4) and oxidized graphite (GOX) synthesized by a simple hydrothermal method to prepare a catalyst (Co3O4/GOX) for the OER. Time-dependent oxidation of graphite (G) and Co3O4 nanoparticles was observed by physical and electrochemical studies. The optimal catalyst (Co3O4/GOX-10) demonstrated the best catalytic OER performance with the lowest overpotential of 250 mV to reach 10 mA cm−2 and a small Tafel slope of 67 mV dec-1, which is substantially smaller than that of pristine Co3O4 and Co3O4/G. An efficient synergistic effect between Co3O4 and GOX in the composite catalyst was observed compared to the individual catalysts. The optimal catalyst exhibited high specific activity (1.543 mA cm−2) and turnover frequency (0.474 s−1) compared to the other catalysts in this study. The high catalytic performance of the catalyst is attributed to the presence of oxygen functional groups, which induced a high electrochemical surface area, additional active site exposure, fast electron transfer, and enhanced dispersion of the catalyst. Thus, the synthesized Co3O4/GOX-10 catalyst can replace noble metals as an efficient OER electrocatalyst.