A combined theoretical and experimental investigation on the photocatalytic hydrogenation of CO₂ on Cu/ZnO polar surface

The photocatalytic hydrogenation of CO2 by Cu-deposited ZnO (Cu/ZnO) polar surfaces is investigated through density functional theory (DFT) calculations combined with experimental work. The DFT results demonstrate that, without Cu-loading, CO2 and H-2 present weak physisorption on the clean ZnO polar surface, except that H-2 undergoes strong chemisorption on the ZnO(0001) surface. Cu deposition on the ZnO polar surface could remarkably enhance the CO2 chemisorption ability, due to the induced charge redistribution on the interface of the Cu/ZnO polar surface systems. Additionally, a Cu-nanoisland, which was simulated using a Cu(111) slab model, exhibited strong ability to chemically adsorb H-2. Thus, H-2 may act as an adsorption competitor to CO2 on the Cu/ZnO(0001), while, in contrast, CO2 and H-2 (syngas) may have more opportunity to simultaneously adsorb on Cu/ZnO(0001) to promote the CO2 hydrogenation. These facet-dependent properties lead us to assume that Cu/ZnO(0001) should be a favorable photocatalyst for CO2 hydrogenation. This assumption is further verified by our photocatalysis experiment based on a ZnO single crystal. According to the theoretical and experimental results, the optimal HCOO* reaction pathway for the photocatalytic hydrogenation of CO2 on Cu/ZnO(0001) is proposed. In this optimal HCOO* path, the hydrogenation of CO2* step and hydrogenation of HCOO* step could be promoted by the coupling of a photo-generated spillover proton and a photoelectron on the interface of Cu/ZnO(0001). This research demonstrates the feasibility of the photocatalytic reduction of CO2 on Cu/ZnO(0001), and will help to develop related high-efficiency catalysts.