A combined theoretical and experimental investigation on the photocatalytic hydrogenation of CO ₂ 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 H₂ present weak physisorption on the clean ZnO polar surface, except that H₂ undergoes strong chemisorption on the ZnO(0001̄) 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 H₂. Thus, H₂ may act as an adsorption competitor to CO₂ on the Cu/ZnO(0001̄), while, in contrast, CO₂ and H₂ (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.