Alpha‐Nickel Hydroxide Coating of Metallic Nickel for Enhanced Alkaline Hydrogen Evolution

In this work, alkaline hydrogen evolution reaction (HER) processes of three typical nickel-based electrocatalysts [i. e., Ni, α-Ni(OH)₂ , and β-Ni(OH)₂ ] were investigated to probe critical factors that determine the activity and durability. The HER activity trend was observed as Ni≫α-Ni(OH)₂ >β-Ni(OH)₂ , likely attributed to a synergy between metallic Ni and Ni(OH)₂ components on the Ni surface and fast water dissociation kinetics on the α-Ni(OH)₂ surface. With the HER proceeding, the metallic Ni surface, however, gradually became α-Ni(OH)₂ , and α-Ni(OH)₂ surface ultimately transformed into β-phase, leading to a dramatic activity decrease of Ni electrodes. Therefore, Ni electrodes were coated with α-Ni(OH)₂ nanosheets to slow down the nickel hydroxylation and optimize the surface ratio of Ni(OH)₂ to metallic Ni. This simple coating procedure enhanced both activity and durability of Ni electrocatalysts.