Boosting Electroreduction of CO2 over Cationic Covalent Organic Frameworks: Hydrogen Bonding Effects of Halogen Ions.

We present the first example of charged imidazolium functionalized porphyrin‐based covalent organic framework (Co‐iBFBim‐COF‐X) for electrocatalytic CO2 reduction reaction, where the free anions (e.g. F−, Cl−, Br−, and I−) of imidazolium ions nearby the active Co sites can stabilize the key intermediate *COOH and inhibit hydrogen evolution reaction. Thus, Co‐iBFBim‐COF‐X exhibits higher activity than the neutral Co‐BFBim‐COF, following the trend of F−<Cl−<Br−<I−. Particularly, the Co‐iBFBim‐COF‐I− showed nearly 100 % CO2 selectivity at a low full‐cell voltage of 2.3 V, and achieved a high CO2 partial current density of 52 mA cm−2 with a turnover frequency of 3018 h−1 at 2.4 V in the anion membrane electrode assembly, which is 3.57 times larger than that of neutral Co‐BFBim‐COF. This work provides new insight into the importance of free anions in the stabilization of intermediates and decreasing the local binding energy of H2O with active moiety to enhance CO2 reduction reaction. [ABSTRACT FROM AUTHOR]