First-principles prediction of a direct Z-scheme WSe2/HfS2 van der Waals heterostructure for overall photocatalytic water decomposition

Abstract

Direct Z-scheme heterostructure photocatalyst has been validated as an efficacious approach for addressing energy source issues and environmental challenges. This manuscript employs a first-principles approach to scrutinize single-layer WSe₂ and HfS₂ materials, culminating in the successful construction of a direct Z-scheme WSe₂/HfS₂ van der Waals (vdW) heterostructure. Herein, we present a comprehensive investigation regarding the structural stability, electronic characteristics, and photocatalytic efficacy of this heterostructure. The findings indicate that the WSe₂/HfS₂ heterostructure exhibits exemplary thermodynamic stability, thereby endorsing its viability for subsequent experimental synthesis. Characterized by a type-II energy band arrangement, the heterostructure manifests a band gap of 0.63 eV that is much smaller than 2.15 eV and 1.94 eV for individual WSe₂ and HfS₂ monolayers, respectively, together with the band edge positioning conforming to the prerequisites for overall water-splitting. Additionally, the built-in electric field from the WSe₂ side to the HfS₂ side and the band bending in the charged region induce direct Z-scheme charge transfer, thereby effectively enhancing redox reaction kinetics. Through the calculation of free energy changes in intermediate products during the redox process, we corroborate the high photocatalytic activity of the heterostructure. Ultimately, we demonstrate the exceptional optical absorption performance of the WSe₂/HfS₂ heterostructure, coupled with excellent solar-to-hydrogen (STH) efficiency, η_STH, within the visible light spectrum. Notably, the optical absorption ability and STH efficiency are further enhanced under the application of biaxial compressive strain. In conclusion, the outcomes of this inquiry affirm the expansive application potential of the WSe₂/HfS₂ heterostructure in the realm of water decomposition.