Abstract
<title>Abstract</title> <p> Photocatalytic CO <sub>2</sub> reduction to solar fuels represents a promising strategy for carbon resource recycling. Nevertheless, its efficiency and product selectivity remain limited by the severe recombination of photogenerated carriers, inefficient CO <sub>2</sub> activation, and slow kinetics of multi-electron reduction processes. This study reports the construction of a Cu <sub>2</sub> O/Bi <sub>2−x</sub> WO <sub>6</sub> p-n heterojunction photocatalyst with engineered Bi vacancies to synergistically optimize charge transfer and CO <sub>2</sub> reduction pathways through defect engineering and interface construction. A well-defined hetero-interface forms between Cu <sub>2</sub> O and Bi <sub>2−x</sub> WO <sub>6</sub> , where Bi vacancies modulate the local electronic structure. Meanwhile, the p-n heterojunction further promotes interfacial charge separation and directional migration. The optimized 20Cu <sub>2</sub> O/Bi <sub>2−x</sub> WO <sub>6</sub> exhibits significantly improved photocatalytic CO <sub>2</sub> reduction performance, achieving CO and CH <sub>4</sub> generation rates of 18.43 and 6.18 µmol·h <sup>− 1</sup> ·g <sup>− 1</sup> , respectively, far exceeding those observed for pure Bi <sub>2−x</sub> WO <sub>6</sub> or Cu <sub>2</sub> O. As revealed by in situ infrared spectroscopy and DFT calculations, the composite system facilitates CO <sub>2</sub> activation and *CO formation while substantially lowering the thermodynamic barrier for *CO to *CHO conversion, thereby promoting deeper hydrogenation pathways and enabling CH <sub>4</sub> production. Thus, this study demonstrates that synergistic regulation by Bi vacancies and p-n heterojunctions effectively enhances both CO <sub>2</sub> photoreduction activity and product selectivity, offering novel insights for designing high-performance bismuth-based photocatalysts. </p>