Steric effects of CN vacancies for boosting CO₂ electroreduction to CO with ultrahigh selectivity

In the electrochemical reduction of CO₂ 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 H₂ cold plasma bombardment to improve the CO₂RR 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 CO₂RR. 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 CO₂RR into a single product.