Theoretically designing of polar van der Waals heterostructure for photocatalytic overall water splitting

Abstract

Conventional photocatalysts for overall water splitting face significant material selection constraints due to stringent bandgap requirements. To address this limitation, we propose an innovative strategy utilizing the intrinsic built-in electric field of two-dimensional (2D) polar materials to induce band bending. In this work, we constructed ten two-dimensional polar van der Waals (vdW) heterostructures by integrating five nonpolar materials (MoO2, WO2, PdO2, Ti2CO2, and TiF2) and Al2O3 monolayers with different polarization directions. These five nonpolar materials were identified from 4254 candidates through first-principles calculations combined with a material-screening strategy. The incorporation of the polar Al2O3 layer disrupts the structural symmetry of the heterostructures, leading to an electrostatic potential difference between two surfaces, which in turn gives rise to an internal built-in electric field. It is interesting that Ti2CO2/Al2O3-P↓ and WO2/Al2O3-P↓ (symbol ↓ denotes polarization direction of Al2O3 layer) heterostructures are direct band gap semiconductors with strong optical absorption and suitable band edge positions with respect to the redox potentials of water. More importantly, the Ti2CO2/Al2O3-P↓ and WO2/Al2O3-P↓heterostructures exhibits impressive solar-to-hydrogen (STH) conversion efficiencies of 23.35% and 21.96%, respectively, highlighting their great potential for photocatalytic applications. These results provide a new strategy for designing polar vdW heterostructures with tunable built-in electric fields to achieve efficient charge separation and high photocatalytic water splitting performance.