Reversible Switching Cu II /Cu I Single Sites Catalyze High-rate and Selective CO 2 Photoreduction.

Herein, we first design a model of reversible redox-switching metal-organic framework single-unit-cell sheets, where the abundant metal single sites benefit for highly selective CO 2 reduction, while the reversible redox-switching metal sites can effectively activate CO 2 molecules. Taking the synthetic Cu-MOF single-unit-cell sheets as an example, synchrotron-radiation quasi in situ X-ray photoelectron spectra unravel the reversible switching Cu II /Cu I single sites initially accept photoexcited electrons and then donate them to CO 2 molecules, which favors the rate-liming activation into CO 2 δ- , verified by in situ FTIR spectra and Gibbs free energy calculations. As an outcome, Cu-MOF single-unit-cell sheets achieve near 100 % selectivity for CO 2 photoreduction to CO with a high rate of 860 μmol g -1  h -1 without any sacrifice reagent or photosensitizer, where both the activity and selectivity outperform previously reported photocatalysts evaluated under similar conditions.