Selective Electrochemical Urea Synthesis from Nitrate and CO2 Using In Situ Ru Anchoring onto a Three-Dimensional Copper Electrode

Urea (CO(NH2)2) is the most common nitrogen fertilizer that is promoting food production worldwide due to its high nitrogen content. However, the conventional urea synthesis involving hydrogenolysis of nitrogen and C-N bond coupling requires harsh conditions and a massive carbon footprint. Herein, we report a promising technology for the green synthesis of urea using nitrate (NO3-) and carbon dioxide (CO2) under ambient conditions over Ru/Pt/Pd-modified three-dimensional copper foam (Ru/Pt/Pd-Cu CF) electrode. The Ru-Cu CF catalyst delivers a high urea yield of 151.6 mu g h-1 cm-2 at a low onset potential of -0.3 V vs Ag/AgCl (0.13 V vs RHE) as well as an FE of 25.4%, surpassing that of Pt/Pd-Cu CF. Moreover, it is confirmed by operando electrocatalytic Raman spectroscopy and theoretical calculations that the *COOH intermediate is the rate-determining step of C-N bond coupling. Benefiting from the partial 3d states of surface Ru sites, the Ru-Cu CF electrode possesses the lowest formation energy of the *COOH intermediate to accelerate the urea synthesis. This work provides an extraordinarily sustainable strategy for green urea synthesis.