C-N Coupling Enabled by N-N Bond Breaking for Electrochemical Urea Production

Urea electrosynthesis under mild conditions has emerged as a promising alternative strategy to replace the harsh industrial HaberBosch process, which is however limited by sluggish C-N coupling and low selectivity. Here, a novel mechanism based on the synergistic effect of N-N bond cleavage and C-N coupling for highly efficient urea production is proposed. It is found that dual vanadium atoms anchoring onto defective graphene (V2N6) can activate the adsorbed *N2, in which the stable N & EQUIV;N bond can be gradually weakened until being broken after two protonation steps, with superior thermodynamic and kinetic feasibility. CO molecules can be easily adsorbed on the dissociated *NH, followed by an exothermic C-N coupling to form the urea precursor *NHCONH with a low kinetic energy barrier of 0.20 eV. The dual-atom V2N6 not only exhibits superior intrinsic activity for urea formation, with a limiting potential of -0.26 V, but also can significantly suppress the competitive N2 reduction and hydrogen evolution reactions. This study presents a new avenue for developing novel mechanisms and efficient catalysts for urea electrochemical synthesis. The V2N6 dual atom catalyst exhibits efficient electrocatalytic activity for urea production from N2 and CO, which is attributed to a unique mechanism that involves the synergistic effect of NN bond cleavage and CN coupling. The inert N & EQUIV;N bond gradually weakens and eventually breaks after two protonation steps, facilitating the facile CN coupling from two dissociated *NH and CO molecules.image