Insight into synergetic mechanism of Au@Pd and oxygen vacancy sites for coupling light-driven H2O oxidation and CO2 reduction

Photocatalytic reduction of CO2 with H2O into CH4 is a promising way to realize solar energy utilization and CO2 conversion, in which the key issue is how to enhance and couple CO2 reduction as well as H2O oxidation. In this work, we precisely fabricated a binary functional photocatalyst by loading Au@Pd nanoparticles onto Vo-rich TiO2 through a surfactant-free deposition-reduction method, whose fine structure was confirmed by aberration-corrected HAADF-STEM, EELS, EPR and XPS. Combining photocatalytic performance with a series of in situ FTIR measurements, we clarified the role of metallic sites and semiconductor support in coupling CO2 reduction and H2O oxidation. Specifically, H2O oxidation process was facilitated by the Vo-rich TiO2 to contribute more protons, followed by the activation of CO2 and protons primarily by the metallic Au@Pd sites to form the surface bounded Au@Pd-CO2 center dot- and Au@Pd-H species. By adjusting the ratio of Au@Pd nanoparticles and V-O concentration to manipulate the Au@Pd-C-2(center dot-)/Au@Pd-H ratio, CH4 yield of 26.32 mu mol/(g.h) and selectivity of electron toward CH4 of 96% can be observed with minimal concomitant H-2 generation. These findings could open a feasible and universal route to enhance the photocatalytic efficiency of CO2 conversion. (C) 2019 Elsevier Inc. All rights reserved.