Synergistic Fe-Doping and S-Vacancy Engineering in NiS2 for High-Performance Water Splitting

Cost-effective and high-performance bifunctional electrocatalysts are essential for efficient water splitting; however, challenges such as high overpotentials, limited active sites, and poor stability, especially in seawater, remain unresolved. Here, we report a scalable and low-cost strategy to synthesize a three-dimensional Fe-doped nickel sulfide nanosheet electrocatalyst with sulfur vacancies (Fe-NiS2@NaBH4) grown on nickel foam. The combined use of Fe electrodeposition and NaBH4 treatment enables simultaneous Fe incorporation and sulfur vacancy formation, which optimizes the electronic structure and enhances intermediate adsorption and charge/mass transfer. As a result, the catalyst achieves overpotentials of 114 and 233 mV for HER and OER at 10 mA cm–2 in 1 M KOH and a cell voltage of 1.567 V at 10 mA cm–2 in a two-electrode configuration. It also exhibits long-term durability, with only 1.065% current decay after 360 h at 100 mA cm–2, and maintains stability in simulated seawater. Mechanistic studies reveal a synergistic effect between Fe-doping and sulfur vacancies: in situ Raman spectroscopy confirms the promotion of *OH to *OOH conversion during OER, while DFT calculations indicate reduced energy barriers for HER and OER with both modifications. This study provides mechanistic insights into cooperative catalytic effects and presents a viable pathway toward large-scale hydrogen production in alkaline and saline environments.