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 CO2 into urea under ambient conditions represents a promising alternative process. But it was still limited by the strong competition between nitrate electrochemical reduction (NO3ER) and CO2 electrochemical reduction (CO2ER). Here, FeII-FeIIIOOH@BiVO4-n heterostructures are constructed through hydrothermal synthesis and exhibited superior performance toward urea electrosynthesis with NO3− and CO2 as feedstocks. The optimized urea yield and Faradaic efficiency over FeII-FeIIIOOH@BiVO4-2 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 BiVO4 (2.0 mmol h−1 g−1 and 5.4%), and the other FeII-FeIIIOOH@BiVO4-n (n = 1, 3, 5) heterostructures. Systematic experiments have verified that BiVO4 and FeOOH are subreaction active sites towards simultaneous CO2ER and NO3ER, respectively, achieving co-activation of CO2 and NO3− on FeII-FeIIIOOH@BiVO4-2. 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 CO2 emission and nitrate pollution but also presents an efficient catalyst for synergistic catalysis towards sustainable urea synthesis.