Rapid Fabrication of Cobalt/Cobalt Oxide Heterostructured Catalysts for Efficient Electrochemical Water Splitting

Metal/carbon-based nanocomposites have attracted significant interest for electrochemical water splitting due to their unique interfacial electronic structures, abundant active sites, and catalytic bifunctionality toward both hydrogen evolution reaction (HER) and oxygen evolution reaction (OER). Herein, Co/CoO-rGO composites consisting of Co/CoO heterostructured nanoparticles encapsulated within a graphitized carbon scaffold are produced via magnetic induction heating at controlled currents for 10 s with cobalt(II) nitrate and reduced graphene oxide (rGO) loaded on nickel foam and effectively catalyze both HER and OER in alkaline media. Among the series, the sample prepared at 400 A for 10 s exhibits the best performance, featuring an overpotential of -144 mV for HER and +390 mV for OER at 10 mA cm^{- 2} and 50 mA cm^{- 2}, respectively. The bifunctional activity can then be exploited for full water splitting, where a low cell voltage of 1.61 V is needed to generate a current density of 10 mA cm^-2, 260 mV better than that with commercial Pt/C and RuO₂. The remarkable performance is attributed to the synergistic interaction between the Co and CoO domains, enhanced charge transfer at the heterojunction interface, and conductive carbon support. These results highlight the potential of Co/CoO-based nanocomposites as efficient and low-cost catalysts for overall water splitting and the scalability of the MIH technology.