Steric effects of CN vacancies for boosting CO 2 electroreduction to CO with ultrahigh selectivity.

In the electrochemical reduction of CO 2 to CO, controlling the binding of the *COOH intermediate is key to adjusting the selectivity and catalytic activity of the CO product. Herein, we report that CN vacancies were used to control the binding of the *COOH intermediate on a Co PBA-V CN catalyst treated by H 2 cold plasma bombardment to improve the CO 2 RR into CO. The CN vacancies can tune the local electronic structure and coordination environment of Co III -CN-Co II (Co-PBA-V CN ) with a high CO faradaic efficiency close to 100% with remarkable durability (>87 h), and a low onset overpotential of 0.17 V in CO 2 RR. The steric effects of the V CN can decrease the free energy barrier of the rate limiting step for the formation of *COOH which can further crack into *CO on the active site of the Co near the V CN . This work provides a new strategy to tune the binding of the *COOH intermediate on the catalyst surface by new vacancies of V CN to enhance the CO 2 RR into a single product.