Defect-activated basal plane engineering in BP/MX ₂ heterostructures enhances photocatalytic performance

Abstract Two-dimensional van der Waals (vdW) heterostructures, particularly those integrating high-mobility black phosphorus (BP) with transition metal dichalcogenides (MX 2 ), demonstrate great potential in photocatalysis for hydrogen evolution and optoelectronic applications. However, chalcogen vacancies are inevitably introduced during synthesis, and their precise role in modulating the interfacial electronic structure and optoelectronic properties remains insufficiently understood from a theoretical perspective. Using first-principles calculations, this work systematically reveals the mechanistic effects of chalcogen vacancies on the electronic and optical properties of BP/MX 2 heterostructures. The introduction of vacancies leads to band gap narrowing and induces localized gap states below the conduction band minimum (CBM), accompanied by an upshift of the Mo 4+ d-band center, which enhances reactant adsorption and thereby improves photocatalytic hydrogen evolution performance. Furthermore, vacancies introduce defect levels near the CBM within the bandgap, which act as electron-trapping centers, promoting electron localization and effectively activating the originally inert basal plane. This discovery provides fundamental theoretical insights into defect engineering of vdW heterostructures, offering important guidance for the rational design of materials for photocatalysis, infrared photodetection, and renewable energy technologies.