Cu 2 O modified ultrathin TiO 2 nanosheets optimizes *COOH formation energy for highly selective photocatalytic CO 2 -to-CH 4 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 photo-generated 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 *CHOx 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.