Electron transfer in Cu/Cu2O generated by disproportionation promoting efficient CO2 photoreduction

Constructing a high-efficiency composite material for CO2 photoreduction is a key step to the achievement of carbon neutralization, but a comprehensive understanding of the factors that dictate CO2 reduction activity remains elusive. Here, we constructed a series of Cu in situ combined on Cu2O (Cu/Cu2O-1, -2, -3) via an acid disproportionation method with various processing time. The optimal photocatalyst (Cu/Cu2O-2) affords CO at a rate of 10.43 µmol·g−1·h−1, which is more than fourfold to that of pristine Cu2O. Electron transfer in the samples was detected by X-ray absorption spectroscopy (XAS) as well as X-ray photoelectron spectroscopy (XPS). Interestingly, the best photoreduction performance was not achieved by the sample possessing the most electron transfer (Cu/Cu2O-1) but by the one with moderate electron transfer (Cu/Cu2O-2). By virtue of density functional theory (DFT) calculations, a linear relationship between Bader charge variation (Δq) of the active sites and adsorption energy of CO2 reduction intermediates was discovered, wherein the moderate charge transfer corresponds to appropriate adsorption energy, which benefits CO2 photoreduction activity substantially. This work provides guidance for the construction of composite catalysts for efficient CO2 photoreduction in a perspective of the quantity of electron transfer.