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.