Gaseous CO 2 Coupling with N-Containing Intermediates for Key C–N Bond Formation during Urea Production from Coelectrolysis over Cu

Coelectrolysis of CO 2 with simple nitrogen compounds can generate molecules containing C–N bonds, which makes it an appealing method for increasing the value and scope of products obtained from CO 2 electrochemical reduction (CO 2 ER) alone. In this study, we used density functional theory (DFT) calculations combined with a constant electrode potential model to investigate C–N formation pathways in the coreduction of CO 2 and NO 3 – /NO 2 – to produce urea on Cu(111). Strikingly, we found that the first C–N bond is formed through coupling of gaseous CO 2, rather than an intermediate of CO 2 ER, with the surface-bound N 1 intermediates (i.e., *NO 2, *NOH, *N, *NH, and *NH 2 ) generated during NO 3 – /NO 2 – reduction to NH 3 . The reaction follows the Eley–Rideal mechanism and requires only a single active site. This result is in contrast with the literature, where the carbon species for C–N coupling were assumed to be intermediates from CO 2 ER to CO (i.e., *COOH and *CO). Further barrier decomposition analysis indicated that the facile kinetics of C–N coupling involving CO 2 are due to the lower energy cost to deform CO 2 and the N 1 intermediate to the transition-state structure as well as the attractive interaction between them. For these facile and hence important CO 2 + N 1 reactions, we determined that the kinetic barrier of C–N coupling correlates well with the deformation energy of the N 1 intermediate. Based on these insights, two strategies to improve C–N coupling have been proposed.