Tandem Photocatalysis on Highly Dispersed Copper Sites in Bismuth Nanocrystals for Thermodynamic-Optimized Photocatalytic CO 2 -to-CH 4 Conversion

Photocatalytic CO 2 reduction to CH 4 represents a promising strategy for CO 2 utilization and the production of valuable chemical feedstocks. However, this strategy faces significant challenges due to charge recombination and the generation of non-selective reactive intermediates, which lead to parasitic side reactions that compromise both reaction selectivity and yield. In this study, we developed a tandem photocatalytic system featuring highly dispersed copper (Cu) sites within bismuth (Bi) nanocrystals (a CuBi bimetallic catalyst) to optimize the thermodynamic pathway of CO 2 -to-CH 4 conversion on a titanium dioxide (TiO 2 ) surface. This bimetallic catalyst simultaneously enabled directional electron transfer and enhanced photogenerated carrier separation efficiency in the TiO 2 . The optimized CuBi–TiO 2 photocatalyst demonstrated a CH 4 evolution rate of 84.1 μmol g −1 h −1 under sacrificial agent-free conditions, representing a nearly sevenfold improvement over pristine TiO 2, while maintaining a selectivity of 97.3%. Mechanistic studies revealed that the CuBi bimetallic architecture exhibited enhanced electrical conductivity and an appropriate work function, facilitating the formation of an ohmic contact at the CuBi/TiO 2 interface. This interface effectively directional transfer of photogenerated electrons from TiO 2 to active CuBi sites. Density functional theory calculations further indicated that the highly dispersed Cu species within Bi nanocrystals modified the adsorption geometry of CO 2 and significantly increased the binding energy of the *CO. The tandem catalytic cooperation between Bi and Cu sites renders the selective conversion of CO 2 to CH 4 thermodynamically favorable. This study underscores the potential of CuBi bimetallic catalysts to address the selectivity−activity trade-off in CO 2 reduction, providing a promising pathway toward efficient and scalable CO 2 -to-CH 4 conversion technologies.