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

Abstract

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 <i>in situ</i> 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.