Electrochemical Urea Production over Diatomic Fe-Ni Catalyst: a Mechanism for C-N Coupling.

Co-electrocatalytic reduction of CO 2 and nitrate/nitrite as carbon and nitrogen sources to synthesize urea is an effective strategy to solve the energy problem and alleviate environmental pollution. In this work, combined density functional theory calculations with a constant-potential implicit solvent model, we proposed a strategy for the determination of the preferred reaction pathway and the potential window that is guided by the potential-dependent free energy change. It was found that on the FeNi-N 6 -C surface, the C-N coupling occurs between *NHO and the protonated CO 2 in the potential window of -2.43 to -1.34 V for the urea electrochemical production, where the predicted onset potential accords well with the experimental results. The activity originates from the less weak bonding strength of N-O and the negatively charged N atom in *NHO. This study offers a general approach to determining the optimal reaction pathway in electrochemistry and insights into the mechanism of electrochemical synthesis of urea.