Two-dimensional ZnO/ZrXY (X, Y = Br, Cl and F) van der Waals heterostructures as promising photocatalysts for high efficiency water splitting

Abstract

In recent years, hydrogen (H2) energy has been attracting extensive research attention as a clean resource as the energy shortage has become increasingly prominent. Two-dimensional (2D) materials exhibit superior physical and chemical properties compared to their conventional counterparts, hence demonstrating considerable advantages in the water-splitting photocatalyst application. Based on first principle calculations, in this work, monolayered ZnO and ZrXY (X, Y = Br, Cl and F) are combined to form vdW heterostructures and investigate their structural, optical and electronic properties for evaluating their ability to split water photocatalytically. Based on our calculations by two different models (model I and II), ZnO/ZrXY vdW heterostructures exhibit indirect band gaps with a type II band alignment, which benefits the effective spatial separation of photogenerated charge carriers. Bader charge, Charge density difference, and Planner-averaged electrostatic potential analysis suggest that photogenerated charges flow from ZrXY to the ZnO layer are effected by the dipole interface, which prevents the recombination of photogenerated charge carrier and promotes their separation and transfer. Moreover, calculations for optical properties in relation to the dielectric constant's imaginary part indicate that all primary excitation peaks are located in the visible light region, and a red-shift is also observed in ZnO/ZrXY vdW heterostructures. In addition, the band edges of ZnO/ZrXY vdW heterostructures span water redox potentials, which satisfy the requirement of overall photocatalytic water splitting.