Electrochemical urea synthesis by co-reduction of CO2 and nitrate with FeII-FeIIIOOH@BiVO4 heterostructures

Traditional urea synthesis under harsh conditions is usually associated with high energy input and has aroused severe environmental concerns. Electrocatalytic C–N coupling by converting nitrate and CO 2 into urea under ambient conditions represents a promising alternative process. But it was still limited by the strong competition between nitrate electrochemical reduction (NO 3 ER) and CO 2 electrochemical reduction (CO 2 ER). Here, Fe II -Fe III OOH@BiVO 4 - n heterostructures are constructed through hydrothermal synthesis and exhibited superior performance toward urea electrosynthesis with NO 3 − and CO 2 as feedstocks. The optimized urea yield and Faradaic efficiency over Fe II -Fe III OOH@BiVO 4 -2 can reach 13.8 mmol h −1 g −1 and 11.5% at −0.8 V vs. reversible hydrogen electrode, which is much higher than that of bare FeOOH (3.2 mmol h −1 g −1 and 1.3%), pristine BiVO 4 (2.0 mmol h −1 g −1 and 5.4%), and the other Fe II -Fe III OOH@BiVO 4 - n ( n  = 1, 3, 5) heterostructures. Systematic experiments have verified that BiVO 4 and FeOOH are subreaction active sites towards simultaneous CO 2 ER and NO 3 ER, respectively, achieving co-activation of CO 2 and NO 3 − on Fe II -Fe III OOH@BiVO 4 -2. Moreover, the urea synthesis via the *CO and NO* intermediates and C–N coupling was confirmed by the in situ Fourier transform infrared spectroscopy. This work not only alleviates the CO 2 emission and nitrate pollution but also presents an efficient catalyst for synergistic catalysis towards sustainable urea synthesis.