Defect-Engineered Al₂CO/Al₂Se₃ Heterostructure for Enhanced Photocatalytic Water Splitting

In this study, we investigate the influence of intrinsic defects on the photocatalytic properties of the Al₂CO/Al₂Se₃ heterostructure using first-principles calculations. The intrinsic defects in the form of oxygen and carbon vacancies in Al₂CO monolayer and interface Al₂CO/Al₂Se₃ appeared to increase the electronic bandgap; however, aluminum vacancy caused a semiconductor-to-metal transition in the material. The introduction of oxygen vacancies caused charge transfer from Al₂Se₃ to Al₂CO, causing electronic stabilization and revealing the van der Waals interaction in the heterojunction. The band edge alignment of the pristine Al₂CO monolayer indicated unsuitability for hydrogen evolution, but for the heterojunction, the appearance of oxygen vacancies modified the band diagram and the origin of gap states enabling the heterojunction to trigger water reduction. The modeling of photocatalytic water splitting revealed that the heterostructure containing oxygen vacancies supports hydrogen evolution reaction (HER) and oxygen evolution reaction (OER). The HER is found to be thermodynamically promising on Al and Se sites, indicating ΔG of -0.091 eV and -0.144 eV, respectively, whereas the OER presented an overpotential of 1.08 V.