Regulation of Coordination Number over Single Co Sites: Triggering the Efficient Electroreduction of CO 2 .

The design of active, selective, and stable CO2 reduction electrocatalysts is still challenging. A series of atomically dispersed Co catalysts with different nitrogen coordination numbers were prepared and their CO2 electroreduction catalytic performance was explored. The best catalyst, atomically dispersed Co with two-coordinate nitrogen atoms, achieves both high selectivity and superior activity with 94 % CO formation Faradaic efficiency and a current density of 18.1 mA cm-2 at an overpotential of 520 mV. The CO formation turnover frequency reaches a record value of 18 200 h-1 , surpassing most reported metal-based catalysts under comparable conditions. Our experimental and theoretical results demonstrate that lower a coordination number facilitates activation of CO2 to the CO2 .- intermediate and hence enhances CO2 electroreduction activity.