Cu₂O modified ultrathin TiO₂ nanosheets optimizes *COOH formation energy for highly selective photocatalytic CO₂-to-CH₄ conversion

Photocatalytic CO₂ reduction to produce valuable chemicals is a promising strategy to address environmental issues and energy crisis. However, achieving high efficiency and selectivity for converting CO₂ into higher-energy CH₄ remains challenging due to the competitive two-electron reduction pathway producing CO. In this study, Cu₂O clusters were strongly anchored onto ultrathin TiO₂ nanosheets (Cu(I)-TiO₂) using a simple photo-deposition method. Compared to pure TiO₂, Cu(I)-TiO₂ samples exhibited a significantly enhanced photocatalytic activity and selectivity for CO₂-to-CH₄. The presence of Cu₂O can also enhance the photogenerated carrier separation and light absorption. By optimizing the amount of Cu₂O, the CH₄ production rate of 45.73 μmol·g⁻¹·h⁻¹ with selectivity up to 97.47% was achieved. Mechanistic investigations demonstrate that the presence of Cu₂O lowers the formation energy barrier of *COOH, a key intermediate for the photocatalytic CO₂ reduction. Moreover, Cu(I)-TiO₂ promotes the adsorption and hydrogenation of *CO to *CHO_x species, favoring CH₄ production over CO. This work provides valuable insights for designing highly efficient and selective photocatalyst for CO₂ reduction and deepens the understanding of reaction mechanism.