Poor electronic conductivity and an inert basal plane restrict the further enhancement of hydrogen evolution reaction (HER) in 2H-phase MoSe 2 . Herein, we synthesized MoSe 2 nanosheet arrays on carbon cloth and induced multivacancies in their basal plane via high-energy Ar 2+ beam irradiation, which are confirmed by Raman, electron spin resonance, X-ray photoelectron spectroscopy, and highresolution transmission electron microscopy analyses. Electrical measurement results indicate that these vacancies in the MoSe 2 basal plane can effectively improve their electrocatalytic performance, where the lowest overpotential of −171 mV at the current density of −100 mA/cm 2 and Tafel slope of 35 mV/dec were achieved in Ar 2+ -irradiated (dose of 5 × 10 15 ions/cm 2 ) MoSe 2 nanosheets. First-principles calculation results reveal that different cases of native vacancies in the MoSe 2 basal plane could effectively enhance the conductivity of MoSe 2 and produce more catalytic active sites for hydrogen evolution, giving rise to the better electrocatalytic capacity in the HER process. This finding opens the strategy of vacancy engineering for efficient hydrogen evolution in other transition metal dichalcogenide-based electrocatalysts.

The oxygen evolution reaction (OER) is an essential process in water splitting, which is highly relevant to the new generation of energy exploration approaches. N+ ions irradiation is an effective method for improving the OER electrocatalytic capacity of NiO.

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