Rapid Energy Exchange between In Situ Formed Bromine Vacancies and CO(2) Molecules Enhances CO(2) Photoreduction

Photocatalytic reduction of CO(2) into fuels provides a prospective tactic for regulating the global carbon balance utilizing renewable solar energy. However, CO(2) molecules are difficult to activate and reduce due to the thermodynamic stability and chemical inertness. In this work, we develop a novel strategy to promote the adsorption and activation of CO(2) molecules via the rapid energy exchange between the photoinduced Br vacancies and CO(2) molecules. Combining in situ continuous wave-electron paramagnetic resonance (cw-EPR) and pulsed EPR technologies, we observe that the spin–spin relaxation time (T(2)) of BiOBr is decreased by 198 ns during the CO(2) photoreduction reaction, which is further confirmed by the broadened EPR linewidth. This result reveals that there is an energy exchange interaction between in situ formed Br vacancies and CO(2) molecules, which promotes the formation of high-energy CO(2) molecules to facilitate the subsequent reduction reaction. In addition, theoretical calculations indicate that the bended CO(2) adsorption configuration on the surface of BiOBr with Br vacancies caused the decrease of the lowest unoccupied molecular orbital of the CO(2) molecule, which makes it easier for CO(2) molecules to acquire electrons and get activated. In situ diffuse reflectance infrared Fourier transform spectroscopy further shows that the activated CO(2) molecules are favorably converted to key intermediates of COOH*, resulting in a CO generation rate of 9.1 μmol g(−1) h(−1) and a selectivity of 100%. This study elucidates the underlying mechanism of CO(2) activation at active sites and deepens the understanding of CO(2) photoreduction reaction.