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

Abstract

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─In dual metal sites by strong coordination of hydroxyl O and imine N atoms in the framework. It is found that the optimal CuIn_1.07-COF electrocatalyst exhibits an impressive urea yield rate of 2924.4 µg 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.