Dual-Defect Donor–Acceptor Pairing in Metal Oxide Semiconductors for Enhanced CO 2 Photoreduction

Defect engineering has emerged as a powerful approach to enhance the photocatalytic activity of metal oxides, yet the role of oxygen vacancies, commonly regarded as the Shockley–Read–Hall charge recombination centers, remains controversial. Taking bismuth oxybromide (BiOBr) as a prototypical photocatalyst, we demonstrate a dual-defect strategy incorporating both surface Br (VBr) and bulk O (VO) vacancies to suppress recombination and enhance CO2 reduction. While the VO alone results in significant charge losses, the VBr improves CO2 adsorption and lowers its LUMO to effectively capture photoexcited electrons from the VO-induced defect state for the subsequent reaction. Formation of a donor–acceptor pair between the CO2 LUMO and the valence band maximum facilitates long-lived charge separation due to weak nonadiabatic coupling. The strategy extends to vacancy–transition metal doping, further lowering reaction barriers and advancing defect engineering principles. The study provides a comprehensive understanding of defect-dependent photocatalytic reactions, forming a basis for defect engineering in photocatalysis.