First-principles study of two-dimensional HfS2/GaS van der Waals heterostructure for photocatalytic action

Exploring excellent performance of photocatalysts for hydrogen/oxygen evolution reactions is an effective way for solar energy applications. In this work, a HfS2/GaS van der Waals heterostructure (vdwH) has been designed to achieve efficient and spontaneous water decomposition. Through first-principles calculation, HfS2/GaS vdwH has been proved to be a stable and promising photocatalyst with the following obvious advantages: both water reduction and oxidation potentials are located in the band gap of HfS2/GaS vdwH (2.04 eV), ensuring that water splitting can occur. The type-II band structure and built-in electric field ensure the effective separation of photoelectron-hole, and the high mobility of electrons and holes can also predict high photocatalytic activity. By calculating the free energy of the oxygen evolution reaction on the surface of GaS and the hydrogen evolution reaction on the surface of HfS2 of the heterostructure, it's found that the water decomposition reaction can occur spontaneously under light. Furthermore, after 1-6% in-plane biaxial tensile strain was applied, the redox reaction of photocatalytic decomposition water can still occur on the HfS2/GaS vdwH, and the application of strain can effectively regulate the optical and electronic properties. Therefore, HfS2/GaS vdwH could be a promising candidate material for the photocatalytic decomposition of water.