US EPA

7446645 

Journal Article 

Covalent Organic Frameworks Linked by Amine Bonding for Concerted Electrochemical Reduction of CO2 

Liu, H; Chu, Jun; Yin, Z; Cai, Xin; Zhuang, Lin; Deng, H 

2018 

Elsevier Inc 

4 

7 

1696-1709 

English 

10.1016/j.chempr.2018.05.003 

WOS:000438557200019 

By extending covalent bonds to two-dimensional (2D) and three-dimensional (3D) frameworks, the emergence of covalent organic frameworks (COFs) represents a new and exciting branch in porous and crystalline materials. Currently, the discovery of new linkages and improvement of chemical stability are the two most pressing challenges for the development of COFs. We report the synthesis of an amine-linked COFs in both 2D and 3D forms. These COFs exhibited excellent stability in strong acid and base. Furthermore, by depositing COF-300-AR on a flat silver electrode, we were able to construct a molecularly defined interface for electrochemical reduction of CO2 to CO with high efficiency and selectivity. Spectroscopic studies revealed that the concerted behavior between COFs and the silver electrode at their interface was responsible for the promoted performance. This molecularly defined interface approach improves the selectivity of the electrochemical reaction without sacrificing the overall efficiency. linked covalent organic frameworks (COFs) were synthesized by the reduction of parent imine-linked COFs by crystal-to-crystal transformation. The excellent chemical stability of these COFs in combination with the presence of a large amount of amine functional groups led to a robust and molecularly defined interface at the silver metal surface as an electrode for the electrochemical reduction of CO2. The concerted operation of COF and the metal surface resulted in high conversion efficiency and excellent selectivity against the reduction of water. nt organic frameworks (COFs) with amine linkage in both three and two dimensions, COF-300-AR and COF-366-M-AR, were synthesized by direct reduction of their corresponding COFs with imine linkage, COF-300 and COF-366-M, respectively. The quantitative reduction was confirmed by Fourier transform infrared and cross-polarization magic angle spinning NMR (both 13C and 15N) spectroscopy. These amine COFs were highly crystalline and exhibited excellent chemical stability in strong acids and bases. The abundant amino groups in the COF-300-AR backbone facilitated the electrochemical reduction of CO2 on silver electrodes in a concerted manner and led to selective generation of CO. Specifically, CO conversion efficiency was raised from 13% to 53% at −0.70 V and from 43% to 80% at −0.85 V (versus a reversible hydrogen electrode) in comparison with that of a bare silver electrode. The porosity of COFs favored molecular diffusion to the electrode surface, and the amine functional groups close to the electrode surface promoted CO2 conversion efficiency by forming carbamate intermediates. © 2018 Elsevier Inc. 

amine linkage; chemical stability; covalent organic frameworks; crystal-to-crystal transformation; electrochemical CO2 reduction; molecularly defined interface; SDG13: Climate action; SDG7: Affordable and clean energy