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.