Material design with the concept of solid solution-type defect engineering in realizing the conversion of an electrocatalyst of NiS2 into a photocatalyst for hydrogen evolution

[Display omitted] •The incorporation of In and O into NiS2 to form solid solution in (Ni,In)(O,S)2-x.•The conversion of a low-bandgap electrocatalyst into a high-bandgap photocatalyst.•First report on (Ni,In)(O,S)2-x with different amounts of oxygen vacancies.•Surface oxygen vacancy defect and the Ni2+/Ni3+ state are important for PHER.•Mechanism for (Ni,In)(O,S)2-x with enhanced PHER performance was proposed. The conversion of a lower-bandgap and electrocatalyst-type NiS2 phase into a higher-bandgap and photocatalyst-type one with excellent photocatalytic hydrogen evolution reaction (PHER) is demonstrated. In- and O-added NiS2 (NiInOS) extended its bandgap for harvesting visible light and showed as a distorted pyrite structure with a molecular formula of (Ni0.872In0.128)[(O0.2S0.8)1.5(□)0.5]. (Ni,In)(O,S)2-x with active oxygen vacancy and a partial Ni3+-to-Ni2+ conversion achieves excellent PHER. The best (Ni,In)(O,S)2-x with an oxygen vacancy content of 16.8 % could produce 496.8 μmol/h H2 under visible light, while it was 7.63 μmol/h H2 at a content of 2.12 %. The DFT calculation predicts that surface oxygen vacancies of (Ni,In)(O,S)2-x have a strong interaction with H2O to reach a high water adsorption energy of -0.896 eV. Here, the conversion of NiS2 into photocatalyst indicates that defect engineering by forming solid solution with incorporation of indium and oxygen to have bimetal and bichalcogen (Ni,In)(O,S)2-x is a promising approach for novel materials design to extend material application.