Hydrogen generated by water splitting provides a renewable energy source, but development of materials with efficient electrocatalytic water splitting capability is challenging. Thin-film electrocatalytic material (H 2 −NiCat) with robust water reduction properties, which can be readily prepared by a reduction-induced electrodeposition method from nickel salts in a borate-buffered electrolyte (pH 9.2), is reported. The material consists of nanoparticles with nickel oxide or hydroxide species located at the surface and metallic nickel in the bulk. The catalyst mediates H 2 evolution in a near-neutral aqueous buffer at low overpotential. The catalyst requires a subsequent oxidative pretreatment in order to attain a well-defined hydrogen evolution reaction (HER) activity, and the 1.5 h anodized catalyst film exhibits a HER current density of about 1.50 mA cm −2 at 0.452 V overpotential over a period of 24 h with no observable corrosion. In addition, it can be converted by anodic equilibration into an amorphous Ni-based oxide film (O 2 −NiCat) to catalyze O 2 evolution, and the switch between the two catalytic forms is fully reversible. The robust, bifunctional, switchable, and noble-metal-free catalytic material has immense potential in artificial solar water-splitting devices.

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