Asymmetric Coordination Induces Electron Localization at Ca Sites for Robust CO2 Electroreduction to CO

Abstract

Main group single atom catalysts (SACs) are promising for CO₂ electroreduction to CO by virtue of their ability in preventing the hydrogen evolution reaction and CO poisoning. Unfortunately, their delocalized orbitals reduce the CO₂ activation to *COOH. Herein, an O doping strategy to localize electrons on p-orbitals through asymmetric coordination of Ca SAC sites (Ca-N₃ O) is developed, thus enhancing the CO₂ activation. Theoretical calculations indicate that asymmetric coordination of Ca-N₃ O improves electron-localization around Ca sites and thus promotes *COOH formation. X-ray absorption fine spectroscopy shows the obtained Ca-N₃ O features: one O and three N coordinated atoms with one Ca as a reactive site. In situ attenuated total reflection infrared spectroscopy proves that Ca-N₃ O promotes *COOH formation. As a result, the Ca-N₃ O catalyst exhibits a state-of-the-art turnover frequency of ≈15 000 per hour in an H-cell and a large current density of -400 mA cm^-2 with a CO Faradaic efficiency (FE) ≥ 90% in a flow cell. Moreover, Ca-N₃ O sites retain a FE above 90% even with a 30% diluted CO₂ concentration.

Keywords: CO 2 electroreduction; asymmetric coordination; calcium; electron localization; p-orbital.