Metal Spin‐State and Low‐Crystallinity Integration Enables High‐Current‐Density Hydrogen Evolution on Ni ₃ S ₂ in Alkaline Water and Seawater

Achieving Ni‐based electrodes with high activity and durability under industrial current densities in alkaline water or seawater remains challenging. Ni 3 S 2 , with its unique 8‐electron 3d configuration, facilitates electron transfer and spin‐state tuning, yet high O─H activation barriers and strong H * adsorption limit its HER performance. Here, we propose a “metal spin‐state and low‐crystallinity integration” strategy, where Fe incorporation into Ni 3 S 2 on NiFe foam (Fe‐Ni 3 S 2 /NFF) induces a Ni 2+ spin‐state transition that optimizes d‐orbital occupation and lowers reaction barriers, while simultaneously generating a low‐crystallinity architecture that accelerates charge transfer, modulates H * adsorption, and enhances corrosion resistance. As a result, Fe‐Ni 3 S 2 /NFF delivers low overpotentials of 49 mV at 10 mA cm −2 and 233 mV at 1000 mA cm −2 , and maintains excellent stability for 600 h in 1.0 m KOH and 500 h in alkaline seawater. When employed as both the anode and cathode, it enables overall water splitting at 1.65 and 1.89 V for 100 and 1000 mA cm −2 , respectively, with ultralong‐term durability exceeding 1000 h at 1000 mA cm −2 in 1.0 m KOH, and its industrial potential is validated even in a simulated alkaline water electrolyzer (30% KOH, 60°C) with stable operation for 96 h at 1000 mA cm −2 .