Engineering cycling of Cu/Cu pairs in BiWO nanoflowers for boosting photocatalytic CO reduction.

The photocatalytic reduction of CO represents an effective method for addressing environmental and energy crises. However, the slow migration and rapid recombination of photogenerated carriers have been identified as significant limitations on the efficiency of this process. Herein, we developed the cycling of Cu/Cu pairs in BiWO nanoflowers for boosting photocatalytic CO reduction. Cu is an electron trap that captures electrons to generate Cu, and Cu is unstable and prone to losing electrons to generate Cu in BiWO. The two processes are in concert to realize Cu/Cu cycling, which alters the charge transfer pathway and enhances the effective separation of photogenerated carriers for CO photoreduction reaction. Consequently, Cu-modified BiWO exhibited remarkable photocatalytic performance with the rate of CO and CH production reaching 165.28 and 16.49 μL·g in 3 h, which are 3.34 and 11.53 times that of the pristine BiWO. And the *COOH is the key to triggering the conversion of CO to CO, and *OC-CHOH is the key to forming CH by CC coupling. This work elucidates a dynamic copper valence cycling mechanism, establishing a paradigm for rational design of Cu-modified photocatalysts in solar-driven CO conversion.