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.