Electrochemical activation-induced Co-Ni-Mo-O nanosheets with low crystallinity and abundant active sites for efficient and ultra-stable hydrogen generation.

Co/Ni/Mo-based oxides are promising candidates for the hydrogen evolution reaction (HER). However, these electrocatalysts often exhibit unsatisfactory HER performance due to the lack of active sites. Herein, an in situ electrochemical activation strategy is proposed to modify the surface structure of a Co-Ni-Mo-O catalyst. During the HER in an alkaline electrolyte, the Co-Ni-Mo-O nanosheets display an activation period and a rough layer with low crystallinity is then formed on the surface of Co-Ni-Mo-O nanosheets with the leaching of partial Mo species. Owing to the synergistic catalysis of multiple metal components, a large electrochemically active surface area provided by the rough surface, and fully exposed active sites in the low-crystalline structure, the activated Co-Ni-Mo-O/NF shows favorable HER activity with an overpotential of only 42 mV at -10 mA cm -2 . Furthermore, it remains stable at a large current density of -250 mA cm -2 for more than 400 h, outperforming almost all the oxide-based electrocatalysts. Such an electrochemical reduction activation strategy provides a feasible way for the surface modification and targeted design of advanced catalysts.