A 2D ZnSe/BiOX vertical heterostructure as a promising photocatalyst for water splitting: a first-principles study

Vertical heterostructure is an effective method to regulate the properties of two-dimensional materials that are superior to its individual components due to the interfacial interaction. Here, two-dimensional ZnSe/BiOX (X=Cl, Br, I) vertical heterostructures as a potential photocatalyst for water splitting are systematically investigated by the first-principles calculations. The results indicate that the binding strength of the heterostructure is larger than -17.6 meV/A2, favoring its experimental realization. Furthermore, the phonon dispersion and ab initio molecular dynamics analysis also indicate its good dynamical and thermodynamic stability. Remarkably, the ZnSe/BiOX heterostructures form type-II band alignment with direct band gap range from 1.78 eV to 2.06 eV, which enable the separation of electrons and holes in two different layers upon visible light irradiation. The ZnSe/BiOX heterostructures also show high electron mobility, leading to fast migration of photo-generated electron and extending their lifetimes. The projected band structure, partial density of states, and partial charge densities exhibit that the electrons of VBM and CBM are located at different sides of ZnSe/BiOX heterostructures. According to the Bader charge analysis and charge density difference, there exists internal electric field across the interface, which will effectively promote the separation of the photoinduced electron-hole pairs. The band edge positions of ZnSe/BiOX heterostructures have demonstrated that the band levels of VBM and CBM stride the oxidation and reduction potential for water splitting. In addition, the band gaps and band edge positions of ZnSe/BiOX heterostructures can be tuned by the in-layer biaxial strain. Therefore, our results have suggested that ZnSe/BiOX heterostructures promise potential application for water splitting under visible light as a novel photocatalysis.