Preparation, activity and mechanism of a metallic Cu/TiO2 nanotube array catalyst by a fast solar drying method for photothermal CO2 reduction under concentrating light

Photocatalytic reduction of CO₂ with solar energy can realize a carbon cycle and ultimately this could solve the CO₂ emission problem, while the reported results often suffer a low energy conversion efficiency. In this paper, we report how metallic Cu was loaded on to TiO₂ nanotube arrays by a chemical reduction – solar drying method, and it showed high activity and efficiency in the photothermal environment created by concentrating solar light. With outdoor solar light as the energy source, the maximum yield rate of the total hydrocarbons reaches several thousand of μmol g⁻¹ h⁻¹, including a large amount of C₂ products such as 650.9 μmol g⁻¹ h⁻¹ C₂H₄, 240.2 μmol g⁻¹ h⁻¹ C₂H₆, and 59.4 μmol g⁻¹ h⁻¹ C₂H₂. The maximum solar to chemical energy efficiency reaches 0.20%. A carbene path for the CO₂ photoreduction is then inferred based upon the products' distribution. According to Newton's Second Law, the reasons for such a high reaction rate are simplified into the contribution of the Cu cocatalyst and the strengthening of the concentrating light induced reaction conditions. The results indicate the advantages and potential of the concentrating technology in the CO₂ photoreduction and catalyst preparation, and the deconvolution of the contribution provides a solution for the in depth understanding of photothermal catalysis.