Regulation CN reduction of CO₂ products selectivity by adjusting the number of V sites and mechanism exploration

Photo induced reduction CO₂ into high valuable fuels holds significant importance in the field of sustainable energy and environmental remediation, yet it is still challenging in achieving selectivity with high conversion efficiency, due to the similar reduction potentials of large number possible products. Controlling photocatalytic CO₂ reduction reaction (CO₂RR) intermediates that form photocatalyst surface through catalyst design is crucial. Herein, we have achieved directional CO₂ reduction selectivity CO or CH₄ by regulation of active site, that the single V site g-C₃N₄ (V-CN) are highly selective towards CO, the dual V sites in V-CN/V₂O₃ are the key feature determining towards photocatalytic CO₂RR selectivity to CH₄ (91 %). The in-situ experimental results and DFT calculations suggest that single vanadium (V) active sites exhibit a tendency to weakly bind to either the carbon (C) or oxygen (O) atoms of the adsorbed CO₂ molecule through a mechanism involving hybridization between the 2p orbitals of the CO₂ molecule and the 3d orbitals of the V active site, leading lower electron concentration on V-CN surface, making the two-electron reduction of CO₂ to CO more likely to carry out. Instead, the CO₂ was effectively adsorbed and activated by the formed stable V-C-O-V sites from V-CN/V₂O₃, which could highly stabilize CHO* intermediate and enrich electrons, suggesting the dual sites configuration lowered the activation energy barrier, thus altering the reaction pathway to favor the formation CH₄ instead of CO.

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