A Mo-cation/O-anion doping strategy for creating vacancy defects and cation multivalency to enhance the hydrogen evolution of ZnS under visible light

Abstract

Herein, we designed a stable and photocorrosion-resistant Mo/O co-doped ZnS (labeled as ZnMoOS) catalyst with abundant sulfur vacancy (Vs) defects and bivalent Mo⁴⁺/Mo⁶⁺ states for an effective photocatalytic hydrogen evolution reaction (photo-HER) under visible light. The Mo/O co-doping reduces the band gap of ZnS and extends its visible light absorption range. The hydrazine-driven process adjusts ZnMoOS with appropriate bivalent n(Mo⁴⁺)/n(Mo⁶⁺) states and creates abundant Vs defects. The Vs defects are active sites to capture water molecules and weaken H–O–H bonds for producing protons and H₂ generation. The bivalent n(Mo⁴⁺)/n(Mo⁶⁺) states act as hosts for photogenerated electrons, facilitating the rapid hopping of photogenerated electrons between Mo⁴⁺ ↔ Mo⁶⁺ to transfer for the photo-HER, thereby improving the photo-HER efficiency. DFT calculations reveal that Mo/O co-doping of ZnMoOS with abundant Vs defects and heterovalent Mo⁴⁺/Mo⁶⁺ states significantly facilitates hydrogen desorption and enhances the surface H* generation rate. ZnMoOS-3 with appropriate Mo/O co-doping and regulation with an optimum hydrazine content exhibits an excellent photo-HER rate of 41.6 mmol g⁻¹ h⁻¹ and an AQE of 18.6% at 400 nm, along with good durability and stability. This work provides a strategy for vacancy defects and heterovalent states for designing sulfide catalysts with high photo-HER activity and inhibition of photocorrosion.