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 (V_Br) and bulk O (V_O) vacancies to suppress recombination and enhance CO₂ reduction. While the V_O alone results in significant charge losses, the V_Br improves CO₂ adsorption and lowers its LUMO to effectively capture photoexcited electrons from the V_O-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.