Selective CO2 Photoreduction into C2 Product Enabled by Charge-Polarized Metal Pair Sites.

Selective CO2 photoreduction into a high-energy-density C2 product is still challenging. Here, charge-polarized metal pair sites are designed to trigger C-C coupling through manipulating asymmetric charge distribution on the reduction intermediates. Taking the synthetic partially reduced Co3O4 nanosheets as an example, theoretical calculations unveil the asymmetric charge distribution on surface cobalt sites. The formed charge-polarized cobalt pair sites not only donate electrons to CO2 molecules but also accelerate the coupling of asymmetric COOH* intermediates through lowering the energy barrier from 0.680 to 0.240 eV, affirmed by quasi in situ X-ray photoelectron spectroscopy and Gibbs free energy calculations. Also, the electron-rich cobalt sites strengthen their interaction with O of the HOOC-CH2O* intermediate, which favors the C-O bond cleavage and hence facilitates the rate-limiting CH3COOH desorption process. The partially reduced Co3O4 nanosheets achieve 92.5% selectivity of CH3COOH in simulated air, while the CO2-to-CH3COOH conversion ratio is 2.75%, obviously higher than that in pure CO2.