Gas Phase CO₂ Photoreduction Behaviors over Composites of Galvanostatically Pulse-Deposited Cu₂O Nanoparticles and Anodized TiO₂ Nanotube Arrays

Electrochemically synthesized composites of vertically aligned titanium dioxide (TiO₂) nanotube arrays (TNAs) and cuprous oxide (Cu₂O) nanoparticles (CNPs) are used for studying gas phase CO₂ photoreduction behaviors. Anodized TNA surfaces with an average aperture size of 60 nm are decorated with CNPs using galvanostatic pulse electrodeposition. The nucleation and growth of CNPs are investigated with the help of cyclic voltammetry and potential-time transients. The number of CNPs and their distribution on TNA surfaces are widely altered by adjusting the ON/OFF time, the number of applied current pulse, and the bath temperature. After characterizing structural and physical properties of the prepared CNPs/TNAs samples, in situ observation of CO₂ photoreduction in gas phase over CNPs/TNAs is carried out in a high vacuum. The enhancement in CO₂ photoreduction over CNPs/TNAs samples is observed for the optimized size and the number of CNPs on TNAs. The reaction route of the same is ascertained from the reaction products. The experimental results indicate that the size of CNPs should be comparable to the average pore size of TNAs for promoting CO₂ photoreduction, and the relationship between CO₂ photoreduction and the structural properties of CNPs is further discussed.