Fe-Doped Nickel Sulfide-Engineered NiFe Layered Double Hydroxide Nanohybrids: Exceptional Oxygen Evolution Activity and Durability in Alkaline Freshwater and Simulated Seawater

Developing low-cost, high-efficiency oxygen evolution reaction electrocatalysts is crucial for sustainable green hydrogen production via water electrolysis. Nonetheless, complex synthetic processes, low catalytic activity, and limited durability of catalysts pose significant challenges for industrial-scale applications, particularly in seawater electrolysis, where Cl^--induced chlorine oxidation and electrode corrosion are prominent issues. In this work, we present a one-step hydrothermal method to fabricate NiFe layered double hydroxide@Fe-doped nickel sulfide nanohybrids on nickel foam (NiFe LDH@Ni_<i>x</i>Fe_3-<i>x</i><i>S</i>₂/NF) using sodium thiosulfate as a dual-function precursor (decomposing to <i>S</i>^2- for sulfide formation and SO₄^2- for LDH modification). The optimal catalyst demonstrates exceptional OER performance in alkaline freshwater (1 M KOH) with overpotentials of 191, 229, and 272 mV to achieve 10, 100, and 500 mA cm^-2, respectively, alongside a low Tafel slope of 34.5 mV dec^-1, while maintaining stability for 530 h at 500 mA cm^-2. In alkaline simulated seawater, it shows comparable activity (197/240/306 mV at the same current densities). Additionally, the self-assembled Pt/C/NF||NiFe LDH@Ni_<i>x</i>Fe_3-<i>x</i><i>S</i>₂-2/NF couple delivers 10 mA cm^-2 at 1.520 V for overall water splitting in an alkaline saline electrolyte. The enhanced performance is attributed to synergistic effects of hydroxide/sulfide nanointerfaces, low interfacial resistance, SO₄^2--mediated Cl^- repulsion/OOH* stabilization, and active β-NiOOH formation, underscoring its potential for practical seawater-based green hydrogen production.