Surface Hydroxylation‐Engineered Ni ₃ S ₂ /Ni‐OH Heterostructure for Durable Alkaline Hydrogen Evolution via Facile pH‐Induced Electrodeposition

Abstract The slow kinetics of the water dissociation step and the poor long‐term durability of non‐precious electrocatalysts are major bottlenecks for the alkaline hydrogen evolution reaction (HER). Herein, a facile pH‐induced electrodeposition strategy is proposed to construct a partially hydroxylated Ni ₃ S ₂ /Ni‐OH composite, where ammonium chloride (NH ₄ Cl) is the key factor for the formation of Ni ₃ S ₂ and transformation of Ni(OH) ₂ into hydroxylated metallic nickel (Ni‐OH). The optimized Ni ₃ S ₂ /Ni‐OH exhibits outstanding HER performance, requiring a low overpotential of only 33 mV at 10 mA cm ⁻² and demonstrating remarkable stability for over 1200 h. Experimental results and theoretical calculations reveal that the hydroxyl species on the nickel surface modulate the electronic structure, which lowers the water dissociation energy barrier and regulates hydrogen adsorption strength. Furthermore, the hydroxyl buffer phase promotes facile hydroxyl migration, which is the key mechanism for regenerating active sites and ensuring outstanding durability. When paired with a NiFe layered double hydroxide anode in an anion‐exchange membrane water electrolyzer (AEMWE), the assembled system demonstrates homogeneous operation for 1000 h at 200 mA cm ⁻² in 1 m KOH at 50 °C.