Modulation of active site environment in an embedded CuOx@TiO2 photocatalyst for enhanced hydrogen evolution and CO2 reduction

Abstract

Cocatalyst act as the active site usually plays an important role in both photocatalytic hydrogen evolution reaction (HER) and carbon dioxide reduction reaction (CO2RR). As the size, distribution, location, contact behavior with semiconductor etc. show significant effects for the activity. In this work, the active site environment (aggregation state of the active site of the cocatalyst) was modulated by locating the different amounts of CuOx nanoparticles (NPs) into the porous TiO2 (CuOx@TiO2), which was achieved by calcination of Cu@MIL-125 as the precursor. The composition, morphology, and chemical state of the catalyst were analyzed by a series of characterization methods. The results showed that the embedded CuOx NPs exhibited obviously better dispersion than the externally supported ones, especially at the high loading amount. Cu NPs totally transformed to CuO at the lower loading amount, while it transformed to CuOx with partial Cu (I) species existence at the higher loading amount. Photocatalytic reactions showed that the activity of CuOx@TiO2 was ∼ twice that of the traditional outside loading catalyst CuOx/TiO2 in both HER and CO2RR. The high HER activity was obtained at relatively lower loading capacity (0.200 wt%∼0.500 wt%), while CO2RR was the advantageous reaction at higher loading capacity (5.000∼15.000 wt%). Apparently, CuOx@TiO2 offered a quite different active site environment for the two type of reactions. The embedded structure can provide highly dispersed single active sites for HER at lower loading capacity, while it facilitates the formation of multi-electron environment under irradiation for CO2RR at higher loading capacity. The construction of an appropriate active center environment determines the occurrence of high-efficiency photocatalytic reactions.