Electronic properties and photocatalytic characteristics with high solar-to-hydrogen efficiency in a promising S-scheme Hf2CO2/SiS2 heterojunction: First-principles calculations

Abstract

The structural, electronic, and optical properties of the Hf₂CO₂/SiS₂ heterojunction were analyzed using first-principles calculations, and the effects of biaxial strains on its band structure and optical absorption were also investigated. The results show that the Hf₂CO₂/SiS₂ heterojunction exhibits an indirect bandgap of 1.05 eV and non-trivial band overlap, which facilitates efficient charge separation and transport. Differential charge density analysis reveals charge transfer at the interface, forming an intrinsic electric field that enhances the separation of photogenerated carriers and thereby improves photocatalytic performance. The Hf₂CO₂/SiS₂ heterojunction aligns with the S-scheme heterojunction model, enabling effective separation of photogenerated electron-hole pairs. Optical analysis shows significant light absorption in the UV and visible regions, with a redshift compared to monolayer materials. The predicted solar-to-hydrogen (STH) conversion efficiency of the Hf₂CO₂/SiS₂ heterojunction reaches 55.20 %, highlighting its potential for photocatalytic hydrogen production. Surface modification through elemental doping optimizes hydrogen evolution reaction (HER) activity of the Hf₂CO₂/SiS₂ heterojunction, ensuring exothermic reactions. Under alkaline conditions, the oxygen evolution reaction (OER) process of the Hf₂CO₂/SiS₂ heterojunction is spontaneous. Biaxial strain tuning further optimizes the bandgap and optical absorption properties of the Hf₂CO₂/SiS₂ heterojunction, thereby enhancing its photocatalytic performance. The research provides highly potential candidate materials for exploring efficient hydrogen evolution catalysts.