Enhancement in photocatalytic water splitting using van der Waals heterostructure materials based on penta-layers

Abstract

Recently, van der Waals heterostructures (vdWHs) have been used to improve the performance of 2D materials, enabling more applications. By using first-principles calculations, we have studied the electronic and optical properties of vdWHs composed of penta-siligraphene and other penta-layers (p-Si₂C₄/p-X; X = Si₂N₄, ZnO₂, Ge₂C₄ or SiGeC₄). The stability of the vdWHs is verified by computing their binding energy, vibrational phonon spectra and ab initio molecular dynamics simulations. By assessing the electronic properties, we have found that the p-Si₂C₄/p-ZnO₂, p-Si₂C₄/p-Ge₂C₄ and p-Si₂C₄/p-SiGeC₄ vdWHs are semiconductors with an indirect band gap characterized by type-I band alignment. Meanwhile, the p-Si₂C₄/p-Si₂N₄ vdWH is a quasi-direct band gap semiconductor characterized by type-II band alignment. Bader charge analysis and charge density of p-Si₂C₄/p-Si₂N₄ vdWHs showed that photogenerated electrons move from the p-Si₂N₄ monolayer to the p-Si₂C₄ monolayer limiting the recombination of photogenerated charges and improving the photocatalytic efficiency. Furthermore, the p-Si₂C₄/p-Si₂N₄ vdWH exhibits suitable band edge positions compared to isolated monolayers suggesting its potential applicability in photocatalytic water splitting. The calculated optical absorption revealed that the p-Si₂N₄ monolayer exhibits substantial optical absorption in the ultraviolet (UV) range, while the p-Si₂C₄ monolayer and the p-Si₂C₄/p-Si₂N₄ vdWH show outstanding optical absorption on the order of 10⁵ cm⁻¹ in the visible and UV ranges. More importantly, the p-Si₂C₄/p-Si₂N₄ vdWH can greatly improve the optical absorption in these regions, which leads to high-efficiency usage of solar energy. Our study provides a route to design new vdWHs based on pentagonal monolayers, as well as an efficient photocatalyst for photocatalytic water splitting and optical devices.