The mechanism of enhanced photocatalytic activity for water-splitting of ReS 2 by strain and electric field engineering.

To enhance the photocatalytic water splitting performance of 2D ReS 2 , we theoretically propose a feasible strategy to engineer its band structure by applying strain or an electric field. Our calculated results show that the strains greatly tune the electronic structure of ReS 2 especially band gap and band edge positions, because the strains significantly alter the crystal structure and then cause rearrangement of the surface charge. However, electric fields have little influence on band gap but obviously affect the band edge positions. This is because the electric fields have little effect on the crystal structure of ReS 2 but easily produce an in-plane electric dipole moment. The shifts in band edge position mainly arise from competition between the surface charge and the in-plane electric dipole. For an applied strain, the shifts are dominated by rearrangement of surface charge; for an applied electric field, the shifts are determined by an induced electric dipole moment. Importantly, functionalized ReS 2 with a bi-axial strain of -4% or an electronic field of -0.1 V Å -1 may be good candidates for water-splitting photocatalysts owing to their suitable band edge positions for water splitting, ideal band gaps, good stability, reduced electron-hole recombination and high carrier mobility. We hope our findings will stimulate experimental efforts to develop new photocatalysts based on functionalized ReS 2 .