Rational Design of Fe-Doped Co₄S₃/Ni₃S₂ Mott–Schottky Heterojunction with Tunable Surface Electron Density for Efficient Water Electrolysis

The development of efficient, durable catalysts for the hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) is essential for improving the efficiency of electrochemical water splitting, which is a feasible approach for sustainable hydrogen production. This study employs a simple and efficient approach for growing a Fe-doped Co4S3/Ni3S2 bimetallic sulfide heterostructure directly on nickel foam. The Mott–Schottky heterojunction presents enhanced surface area, higher conductivity, and optimized electronic features, each of which contributes to exceptional catalytic activity. The Fe–Co4S3/Ni3S2 heterostructure demonstrates exceptional bifunctional electrocatalytic activity in alkaline freshwater, requiring exceptionally low overpotentials of 169 mV for the HER and 198 mV for the OER for achieving a current density of 100 mA cm–2. The Fe–Co4S3/Ni3S2 heterostructure serves as an efficient bifunctional electrocatalyst for overall water splitting, exhibiting a current density of 100 mA cm–2 at a cell voltage of merely 1.758 V, with no performance decline after 288 h of steady operation. Additionally, in a urea-assisted electrolyzer, the electrocatalyst achieves an industrially applicable current density of 300 mA cm–2 at a cell voltage of merely 1.692 V, demonstrating exceptional long-term stability. Density functional theory (DFT) simulations indicate that Fe doping optimizes the electronic structure of the Co4S3/Ni3S2 heterostructure by promoting charge transfer, modulating the d-band center position, and minimizing the adsorption energies of crucial reaction intermediates (H*, OH*, and OOH*). These synergistic effects collectively improve the intrinsic catalytic activity, validating the observed experimental performance. This work highlights the effective use of transition metal doping in regulating catalytic properties and provides a feasible approach for the design and development of next-generation high-performance electrocatalysts.