In Situ Incorporation of Vanadium into Interconnected Co ₃ O ₄ Nanopetals: A Facile Route toward Enhanced Bifunctional Electrocatalysts for Overall Water Splitting

Efficient and cost-effective electrocatalysts for the hydrogen and oxygen evolution reactions (HER and OER) are crucial for the production of green hydrogen through water electrolysis processes. Alkaline and seawater electrolysis are of industrial importance, and economic, stable bifunctional catalysts that are easy to process and deploy are urgently required. In this study, we report a facile and cost-effective synthesis strategy for producing vertically aligned, vanadium-incorporated Co3O4 (i.e., V:Co3O4) stacked nanosheets, with an interconnected nanopetal-like morphology. These unique structures feature abundant catalytically active exposed edge sites and oxygen vacancies, collectively boosting the bifunctional (i.e., HER and OER) catalytic activity in both alkaline and natural seawater environments. The introduction of V4+ and V5+ ions induces lattice strain and structural distortion within the Co3O4 matrix, facilitating electronic redistribution, creation of oxygen vacancies, and an increased density of catalytically active sites. The V(60) electrode with optimum vanadium incorporation achieved a very low overpotential of 160 mV at 10 mA/cm2 with a Tafel slope of 98 mV/dec for HER, close to the benchmark Pt/C catalyst. The sample exhibits an overpotential of 310 mV at 100 mA/cm2 with a Tafel slope of 102 mV/dec for OER, outperforming the benchmark RuO2 catalyst under similar operating conditions. In more demanding alkaline natural seawater conditions, it delivered an overpotential of 177 mV at 10 mA/cm2 for HER (Tafel slope: 100 mV/dec) and 345 mV at 100 mA/cm2 for OER (Tafel slope: 138 mV/dec), highlighting its practical applicability. Additionally, the direct growth of this V:Co3O4 catalyst material on a conductive nickel foam substrate enables the fabrication of self-standing binder-free electrodes with minimal labor, and its excellent bifunctional activity and stability in alkaline electrolyte conditions make it well-suited for large-scale water electrolysis processes contributing to a sustainable energy future.