Engineering Se vacancies to promote the intrinsic activities of P doped NiSe2 nanosheets for overall water splitting

[Display omitted] •We simultaneously introduce P doping and Se vacancies in NiSe2 nanosheets.•The synergistic effects of P doping and Se vacancies promote HER activities.•DFT results demonstrate the lower Gibbs free energy of adsorbed H* in A-NiSe2|P.•A low voltage of 1.62 V is achieved at 10 mA cm−2 for overall water splitting. Element doping is a general and effective approach to modify the electrocatalytic performances, but the low intrinsic activity in each electroactive site still limits the further improvements. Herein, we provide an effective strategy by simultaneously introducing P doping and Se vacancies to enhance the intrinsic activities in NiSe2 nanosheet arrays (A-NiSe2|P) through Ar plasma treatment. Owing to the increased active sites and enhanced electrical conductivity, the resulted A-NiSe2|P shows the enhanced hydrogen evolution performances. Theoretical calculations reveal that introduction of Se vacancies plays a significant role in lowering the adsorption free energy of H* in Ni, Se and P sites, leading to promoted intrinsic activities in A-NiSe2|P. Further, A-NiSe2|P as bifunctional electrocatalysts only needs 1.62 V to reach 10 mA cm−2 for overall water splitting. Our study and understanding of A-NiSe2|P may highlight the importance of element doping and vacancies in enhancing the catalytic activities in overall water splitting.