Synergistic Cu-Bi alloy sub-nanoclusters anchored on blue TiO 2 for selective CO 2 photoreduction to CH 4

Abstract Photocatalytic CO2 reduction to CH4 using H2O offers a sustainable route for solar fuel production but remains challenged by the lack of non-noble-metal cocatalysts that are both efficient and selective. Herein, we report a stepwise photodeposition strategy to anchor Cu-Bi alloy sub-nanoclusters (ASNCs, 0.84 ± 0.12 nm) on blue TiO2 (BT) for CO2 photoreduction. The optimal Bi0.4Cu0.6/BT catalyst achieves a CH4 evolution rate of 94.4 μmol g-1 h-1 with 96.9% selectivity under simulated solar irradiation, substantially outperforming monometallic Cu/BT and Bi/BT. The synergistic interaction between Cu and Bi can inhibit the aerial oxidation of metallic Cu0 and Bi0, accelerate the separation of photogenerated electron-hole pairs, and facilitate the adsorption and activation of CO2. Meanwhile, strong interfacial dielectric coupling between the ASNCs and BT support creates interface states (IFS), which enables visible-light-driven hot electron injection, thereby significantly enhancing the charge separation efficiency and overall photocatalytic activity. Furthermore, the Cu-Bi alloy substantially lowers the Gibbs free energy barrier for CO2 adsorption over Cu active sites and establishes a thermodynamically favorable pathway for stepwise hydrogenation of CO2 toward CH4. This work establishes a non-noble-metal alloy sub-nanocluster strategy on defect-engineered TiO2 for efficient and selective CO2-to-CH4 photoreduction.