Theoretical Design of the Electrocatalytic Urea Synthesis from Carbon Dioxide and Nitric Oxides

Recently, electrochemical coreduction of CO2 and NOx has been proposed as a sustainable route for urea synthesis. Although Zn is the best monometallic catalyst, the urea selectivity on Zn is very low. Toward the rational design of catalysts, the reaction mechanism of urea synthesis was unveiled based on an "electric field controlling constant potential" method, which can directly address the effects of explicit solvent, electric field, and electrode potential on reaction intermediates and transition states. We found that the couplings between CO* and NOH* and CONH* and N* are most favorable for the formation of two C-N bonds of urea, respectively. According to this mechanism, we not only reproduced the experimental Faradaic efficiencies of different products on Zn but also rationalized the activity trend of urea synthesis over a set of catalysts. More interestingly, we have revealed that adsorbed N* species on Fe and Mo have an essential promotion on urea production. Guided by the mechanistic insights, we finally proposed a compressive strain engineering to tune the d-band center of Zn, which can decrease the two C-N coupling barriers to 0.06 and 0 eV, respectively, and deliver a remarkable urea Faradaic efficiency (FE) of 88.5% using CO and NO as reactants.