Synergistic Cu-Bi alloy sub-nanoclusters anchored on blue TiO₂ for selective CO₂ photoreduction to CH₄

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 Bi_0.4Cu_0.6/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.