Light-Driven C-C Coupling for Targeted Synthesis of CH 3 COOH with Nearly 100 % Selectivity from CO 2 .

Targeted synthesis of acetic acid (CH 3 COOH) from CO 2 photoreduction under mild conditions mainly limits by the kinetic challenge of the C-C coupling. Herein, we utilized doping engineering to build charge-asymmetrical metal pair sites for boosted C-C coupling, enhancing the activity and selectivity of CO 2 photoreduction towards CH 3 COOH. As a prototype, the Pd doped Co 3 O 4 atomic layers are synthesized, where the established charge-asymmetrical cobalt pair sites are verified by X-ray photoelectron spectroscopy and X-ray absorption near edge spectroscopy spectra. Theoretical calculations not only reveal the charge-asymmetrical cobalt pair sites caused by Pd atom doping, but also manifest the promoted C-C coupling of double *COOH intermediates through shortening of the coupled C-C bond distance from 1.54 to 1.52 Å and lowering their formation energy barrier from 0.77 to 0.33 eV. Importantly, the decreased reaction energy barrier from the protonation of two*COOH into *CO intermediates for the Pd-Co 3 O 4 atomic layer slab is 0.49 eV, higher than that of the Co 3 O 4 atomic layer slab (0.41 eV). Therefore, the Pd-Co 3 O 4 atomic layers exhibit the CH 3 COOH evolution rate of ca. 13.8 μmol g -1  h -1 with near 100% selectivity, both of which outperform all previously reported single photocatalysts for CO 2 photoreduction towards CH 3 COOH under similar conditions.