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

Summary Covalent 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 13 C and 15 N) 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 CO 2 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 CO 2 conversion efficiency by forming carbamate intermediates.