Insights into C–N Bond Formation through the Coreduction of Nitrite and CO2: Guiding Selectivity Toward C–N Bond

The coreduction of CO2 with nitrogen-containing (N-containing) compounds such as nitrite (NO2–) offers a promising pathway for synthesizing valuable C–N molecules like urea. Improving the efficiency of this process relies on the development of electrocatalysts that can effectively steer the electrocatalytic selectivity toward C–N bond formation among various pathways of the coupled CO2 and NO2– reduction reactions. This necessitates the creation of selectivity descriptors that can facilitate rational catalyst design and enable high-throughput screening. In this study, density functional theory (DFT) calculations were employed to conduct a mechanistic investigation on 14 metals, with the aim of developing descriptors to guide or enforce selectivity toward C–N bond formation. The competition between C–N bond formation via various C- and N-containing intermediates, along with their reduction, was examined, leading to the introduction of the C–N Coupling Index to quantify these competitions at different stages of the reaction. It was demonstrated that while most metals favor the reduction of N-containing intermediates, certain metals exhibit a sufficiently low thermodynamic barrier for C–N coupling, aligning with previous experimental observations. Additionally, a negative linear correlation was found between early C–N bond formation barriers via CO2 and *NO2 and the adsorbed carboxyl (*COOH) binding energies, indicating that metals with weaker *COOH binding are more favorable for C–N bond formation. Building on these findings, it was demonstrated that pulsed electrolysis is an effective strategy to enhance selectivity toward early-stage C–N bond formation by stabilizing key intermediates while suppressing competing undesirable reaction pathways. In addition, NO2– was demonstrated to be a superior nitrogen source for early-stage C–N coupling compared to NO3–, particularly when coupled with pulsed electrolysis. Ultimately, this set of selectivity descriptors, combined with pulsed electrolysis, paves the way for the rational design of catalysts that are selective toward C–N bond formation in the coreduction of CO2 and NO2–, and enables the identification of new electrocatalysts through high-throughput screening.