Synergistic Fe-Doping and S-Vacancy Engineering in NiS 2 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-NiS 2 @NaBH 4 ) grown on nickel foam. The combined use of Fe electrodeposition and NaBH 4 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.