Charge Self-Regulation at the Interface Engineering of the Metallic Heterostructure NiCoP@Co₃S₄ for Efficient Alkaline Overall Water Splitting

Developing heterostructures with high electrical conductivity and appropriate adsorption strength for oxygen intermediates is a crucial strategy to reduce the energy consumption of overall water splitting (OWS) and enhance the economic viability of hydrogen energy. This article proposes a novel metallic heterostructure (NiCoP@Co₃S₄) that is in situ grown on nickel foam. The composite of NiCoP and Co₃S₄ not only promotes effective charge transfer in the heterojunction and accelerates the kinetics of the hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) but also optimizes the electronic structure of the catalyst through interface engineering. Density functional theory (DFT) calculations demonstrate that the formation of the heterostructure significantly increases the density of electronic states near the Fermi level (<i>E</i>_F), thereby enhancing conductivity. Moreover, the d-band center of NiCoP@Co₃S₄ shifts closer to <i>E</i>_F, which enhances the binding strength of reaction intermediates to the catalyst's active sites. This shift lowers the reaction activation energy and thus promotes the catalytic process. Experimental results show that the NiCoP@Co₃S₄ heterostructure exhibits excellent performance in both HER (η₁₀ = 62 mV) and OER (η₁₀ = 203 mV). An electrolyzer composed of NiCoP@Co₃S₄ electrodes requires only a potential of 1.48 V to achieve a current density of 10 mA cm^-2. Additionally, it demonstrates good stability over 100 h of testing, outperforming the Pt/C || RuO₂ catalyst (1.51 V@10 mA cm^-2). This work provides an effective approach to achieving efficient water splitting for hydrogen production at low overpotentials through the self-regulation of charge in heterostructures, offering new insights for the design of efficient non-noble metal-based electrocatalysts.