Valence-state engineering of Cu species on TiO2 surfaces for synergistic enhancement of photocatalytic CO2 reduction activity and products selectivity

Copper serves as an exceptional cocatalyst, enhancing CO 2 molecular adsorption-activation and stabilizing reaction intermediates, thus demonstrating remarkable potential in photocatalytic CO 2 conversion to diverse hydrocarbons. However, the complex and variable oxidation states of Cu make the role and mechanism of low-valent Cu species (Cu 0 /Cu + ) in CO 2 photoreduction poorly understood. This study precisely controlled the valence distribution of Cu species on TiO 2 surfaces using a red phosphorus-mediated hydrothermal synthesis strategy, successfully constructing an efficient catalyst for CO 2 photoreduction. The optimized composite exhibits a CH 4 evolution rate of 64.44 μmol·g −1 ·h −1 under simulated sunlight, representing a 54-fold improvement over pristine TiO 2 while maintaining high selectivity of 86 %. The enhanced photocatalytic performance and product selectivity originate from Cu incorporation, which substantially improves light absorption capacity, prolongs charge carrier lifetime, and reduces charge transfer resistance. Combined characterization and DFT calculations conclusively demonstrate that Cu 0 and Cu + serve as the active sites for CH 4 and CO generation, respectively. The key intermediate *CO preferentially desorbs as CO from Cu + sites, while *CO adsorbed on Cu 0 sites undergoes further hydrogenation to form CH 4 . This work provides novel strategies for developing efficient CO 2 photoreduction catalysts and elucidates the atomic-scale mechanistic role of Cu valence states in regulating CO 2 reduction pathways.