DFT study on the mechanism of the CO2-to-CO conversion by Co-quaterpyridine complexes

Molecular Electrostatic Potential (MESP) surface of Co 0 (qpy)CO 2 . In Co 0 (qpy)CO 2 , the negative charges of the two oxygen atoms are very close, which are -0.704 e and -0.706 e respectively, and there is a very negative electrostatic potential (MESP) near the two oxygen atoms. Obviously, in acidic solution, the two oxygen atoms in neutral Co 0 (qpy)CO 2 molecule should be easier to bind with H + ions. • the geometry, electronic structure and catalytic property of Co-quaterpyridine complexes were explored theoretically with DFT. • Only neutral Co-quaterpyridine complexes can bind and activate carbon dioxide in weak acid solution effectively. • the photo-physical properties of some species involved in the reaction were investigated theoretically with TD-DFT. The electrochemical reduction of carbon dioxide has recently attracted global research interests as it can facilitate a sustainable low-temperature redox cycle for energy storage and conversion. Co-quaterpyridine complexes are one kind of the most promising molecular catalysts for highly selective electrochemical CO 2 ‑to‑CO conversion at a very low overpotential. In the present work, the geometry, electronic structure and catalytic property of Co-quaterpyridine complexes were theoretically calculated through density functional theory (DFT). It is found that the initial catalyst [Co II (qpy)] 2+ is reduced to neutral Co 0 (qpy) after receiving two electrons, and only this neutral species can bind and activate carbon dioxide in the presence of weak Brönsted acids effectively. More intriguingly, the catalyst finally recovers to [Co(qpy)CO] 2+ due to the easy release of the formed product CO. Furthermore, the photo-physical properties of some important intermediates involved in the reaction were also investigated using the time-dependent density functional theory (TD-DFT).