Surface Reconstruction of Amorphous Ni─Co─S─O Material with a Functional Gradient Layer for Highly Efficient and Stable Alkaline Hydrogen Evolution

Abstract Alkaline water electrolysis holds potential for large‐scale, high‐purity hydrogen production. However, the slow kinetics of water dissociation and challenging conditions in alkaline environments complicate the search for an electrocatalyst with both high activity and durability. In this study, a highly active and stable amorphous electrocatalyst is introduced, 3Ni─Co─S─O, developed via a straightforward electrodeposition method for alkaline hydrogen evolution reaction (HER). Notably, the surface of the 3Ni─Co─S─O catalyst undergoes a compositional reconstruction during alkaline HER, yet maintains its amorphous structure. This reconstruction spans roughly 6 µm, leading to a gradual decrease in Ni and S content and a corresponding increase in O concentration toward the surface, thereby forming a stable, gradient active layer. Benefitting from this layer and its amorphous nature, the 3Ni─Co─S─O catalyst demonstrates superior alkaline HER activity—requiring only 170 mV to achieve an industrial HER current density of 1000 mA cm ⁻² . It also showcases remarkable stability, with a mere 15 mV increase in overpotential during continuous HER at 300 mA cm ⁻² for 24 h, outperforming the commercial Pt/C catalyst. The research provides a novel approach to designing high‐performance amorphous alkaline HER electrocatalysts cost‐effectively and contributes insights for understanding and developing advanced amorphous catalysts across various applications.