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In this work, alkaline hydrogen evolution reaction (HER) processes of three typical nickel-based electrocatalysts [i.e., Ni, alpha-Ni(OH)(2), and beta-Ni(OH)(2)] were investigated to probe critical factors that determine the activity and durability. The HER activity trend was observed as Ni >>alpha-Ni(OH)(2) > beta-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 alpha-Ni(OH)(2) surface. With the HER proceeding, the metallic Ni surface, however, gradually became alpha-Ni(OH)(2), and alpha-Ni(OH)(2) surface ultimately transformed into beta-phase, leading to a dramatic activity decrease of Ni electrodes. Therefore, Ni electrodes were coated with alpha-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.
Sophia Haussener, Roberto Valenza, Jian Li
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