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

Abstract Main group single atom catalysts (SACs) are promising for CO 2 electroreduction to CO by virtue of their ability in preventing the hydrogen evolution reaction and CO poisoning. Unfortunately, their delocalized orbitals reduce the CO 2 activation to *COOH. Herein, an O doping strategy to localize electrons on p‐orbitals through asymmetric coordination of Ca SAC sites (Ca‐N 3 O) is developed, thus enhancing the CO 2 activation. Theoretical calculations indicate that asymmetric coordination of Ca‐N 3 O improves electron‐localization around Ca sites and thus promotes *COOH formation. X‐ray absorption fine spectroscopy shows the obtained Ca‐N 3 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‐N 3 O promotes *COOH formation. As a result, the Ca‐N 3 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‐N 3 O sites retain a FE above 90% even with a 30% diluted CO 2 concentration.