Atomically dispersed and electron-enriched Cu-O4 active sites on BiOCl atomic layers for high selectivity methanol photosynthesis.

High selectivity photosynthesis of CH3OH via photocatalytic CO2 reduction has been severely challenged by retarded charge carrier dynamics and sluggish multi-electron reaction kinetics. Herein, single Cu atoms (CuSA) were introduced on BiOCl atomic layers (BOCAL) by a facile two-step method of electrostatic self-assembly and pyrolysis for efficient photocatalytic CO2 reduction, with CH3OH selectively produced at an evolution rate of 103.98 µmol g-1 h-1 and a selectivity of 99.14%. This excellent photocatalytic activity should benefit from the atomically dispersed Cu-O4 coordination structure on BOCAL, which could accelerate the separation and migration of photogenerated charge carriers by creating the impurity energy level (IEL) in the forbidden band of BiOCl with a lowered work function. In situ spectral investigations and density functional theory (DFT) calculations unveil that the Cu-O4 coordination structures with electron density increased by photogenerated oxygen vacancies (VO) could act as the active sites to deliver electrons to CO2 molecules for efficient activation, as well as promote CH3OH generation by inhibiting *CO intermediate desorption and reducing the energy barrier of the rate-determining *COH + H → *CHOH step. This work provides a facile approach to the design of electronic structure-tuned single-atom active sites on two-dimensional (2D) nanostructures towards high selectivity CH3OH photosynthesis, and also deepens the understanding of the single-atom and vacancy interaction between active sites and semiconducting supports for efficient CO2 photoreduction.