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

• Published in: Angewandte Chemie International Edition Vol. 62; no. 7; pp. e202215687 - n/a
• Main Authors: Wu, Qiu‐Jin, Si, Duan‐Hui, Wu, Qiao, Dong, Yu‐Liang, Cao, Rong, Huang, Yuan‐Biao
• Format: Journal Article
• Language: English
• Published: Weinheim Wiley Subscription Services, Inc 06.02.2023
• Edition: International ed. in English
• Subjects: Anions; Carbon dioxide; Chemical reduction; CO2 Electrocatalysis; Covalent Organic Framework; Electrodes; Hydrogen Bond; Hydrogen bonding; Hydrogen evolution reactions; Imidazolium; Intermediates; Ions; Porphyrins; Selectivity
• ISSN: 1433-7851; 1521-3773; 1521-3773
• DOI: 10.1002/anie.202215687

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. Charged imidazolium struts were integrated into two‐dimensional cobalt porphyrin‐based covalent organic frameworks (Co‐iBFBim‐COF‐X) creating catalytic pockets with 5,10,15,20‐tetrakis(4‐aminophenyl)‐porphinatocobalt centers and halogen counter ions (e.g., F−, Cl−, Br−, and I−). The free imidazolium anions in the proximity of the active Co sites in the Co‐iBFBim‐COF‐X can stabilize the key intermediate *COOH and inhibit the occurrence of HER through hydrogen bonding.