Rational Design of Bimetallic 2D Covalent Organic Frameworks for Interlayer Electrocatalytic Urea Production from N2 and CO2

Abstract The electrocatalytic synthesis of urea directly from N2 and CO2 offers a potential approach for transforming these gases into highly concentrated nitrogen-containing fertilizer in an environmentally friendly way. Developing electrocatalysts for the simultaneous activation of inert N2 and CO2 followed by C–N coupling for urea synthesis on specific active sites is challenging. Catalysts with dual metal sites have gained major interest in electrocatalysis for their ability to improve active site accessibility and optimize electronic structures. However, precise and controlled incorporation of dual-metal sites into the materials remains a significant challenge for achieving desired catalytic performance. In this work, we systematically integrate Fe3+ and Co2+ into chelation sites ((E)-3-(phenylamino) acrylaldehyde and 2,2′ bipyridyl)) of porous 2D-covalent organic frameworks (Fe–Co@TpBpy), which demonstrates efficient electrocatalysis for urea production from N2 and CO2 in 0.1 M aq. H2SO4 solution. At −0.75 V vs Ag/AgCl, the urea yield rate reaches 11.25 mmol gcat–1 h–1 with a Faradaic efficiency of 22.52%. Density functional theory (DFT) calculation reveals that the bipyridyl attached Co center promotes the adsorption and conversion of CO2 to CO, whereas the Fe center promotes N2 activation and facilitates the C–N coupling between *NH2 and *CO, resulting in the generation of the key intermediate *CONH2, required for urea formation. Furthermore, DFT studies reveal that the interlayer confinement effect in 2D-Fe–Co@TpBpy promotes an energy-efficient C–N coupling mechanism for urea electrosynthesis. The work presents a unique approach for designing and constructing a bimetallic 2D-COF-based electrocatalyst toward electrochemical urea synthesis.