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

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.