Tuning C―N Coupling Mode by Cu―In Dual Metal Sites in Covalent Organic Framework for Enhanced Urea Electrosynthesis

Electrochemical conversion of CO2 and NO3- to high value-added urea is a win-win strategy for both resources and the environment. However, the yield rate and selectivity of urea are still low. In this work, Cu and In metals are grafted into the interlayers of an imine-linked covalent organic framework (COF) to form stable Cu & horbar;In dual metal sites by strong coordination of hydroxyl O and imine N atoms in the framework. It is found that the optimal CuIn1.07-COF electrocatalyst exhibits an impressive urea yield rate of 2924.4 mu g h-1 mg-1 and high Faradaic efficiency (FE) of 54.7% in H-cell, which surpasses that of most previously reported catalysts for urea electrosynthesis. In situ spectroscopy and theoretical calculations reveal that due to the stronger electronic interaction between Cu and In, *NH2 intermediate is generated on the In site from NO3- reduction, and then couples with *CO2 on neighbor Cu site to produce *CO2NH2 with a lower energy barrier, which effectively promotes the electrochemical co-reduction of CO2 and NO3- to urea. The work provides new clues for understanding the structure-performance relationship in urea electrosynthesis.