Robust Hydrogen Production at High Current Density via <i>In Situ</i> Generated MoO ₄ ^2– on Mo-Doped Ni ₃ S ₂ Seawater Electrolysis Catalysts

The development of electrocatalysts that combine high activity with robust resistance to chlorine-induced corrosion remains a critical challenge for seawater electrocatalysis. Herein, we report a Mo-doped Ni3S2 (Mo-Ni3S2) bifunctional electrocatalyst grown in situ on nickel foam via a one-step hydrothermal method. In simulated seawater (1.0 M NaOH + 0.5 M NaCl), the optimal Mo-Ni3S2-50 catalyst exhibits exceptional bifunctional activity, requiring overpotentials of only 290 mV for the oxygen evolution reaction (OER) and 175 mV for the hydrogen evolution reaction (HER) to reach the current density of ±100 mA cm–2. More importantly, in situ characterizations reveal a dynamic equilibrium between Mo dopant dissolution and readsorption of molybdate species (MoO42–) during operation. This self-adaptive process not only enhances the OER activity by optimizing the reaction kinetics but also forms a chloride-repelling protective layer, endowing the catalyst with remarkable corrosion resistance and long-term stability (>300 h for OER at 100 mA cm–2). When assembled in an anion exchange membrane water electrolyzer (AEMWE), the Mo-Ni3S2-50∥Mo-Ni3S2-50 couple delivers excellent overall water splitting performance, requiring 1.7 V at 100 mA cm–2 and maintaining stable operation for over 165 h. This work elucidates a self-adaptive protection mechanism induced by Mo doping, offering a promising strategy for designing efficient and durable catalysts for practical seawater electrolysis and large-scale green hydrogen production.