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

Abstract

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 H2 O with active moiety to enhance CO2 reduction reaction.