Linking CO to Urea Production from CO2 and NO3–/NO2– Co-Electrolysis on Transition Metals

Electrochemical reduction of CO2 (CO2ER) has the potential to advance carbon neutrality and renewable energy storage. Advanced CO2ER catalysts can selectively produce a wide array of products. Their importance is amplified when coreducing CO2 with nitrate/nitrite ions (NO3–/NO2–) to generate organic compounds containing C–N bonds, enhancing product diversity and value. Some transition metals effectively catalyze the coreduction of CO2 and NO3–/NO2– to yield urea. However, a disparity exists between the experimental observations that underscore the significance of CO production in urea synthesis and the theoretical perspectives that dismiss the role of CO in C–N bond creation. To reconcile this disparity, we utilized density functional theory combined with a constant electrode potential model to investigate four facile CO2 + *N1 (the intermediates from NO3–/NO2– reduction to NH3) couplings─representing the primary C–N formation pathways on a range of transition metal surfaces. Our comprehensive study elucidates the relationships among C–N coupling barriers, *N1, and CO adsorption energies. Notably, we found that while CO is not involved in C–N formation, a catalyst's proficiency in generating CO from CO2ER is indicative of its reduced adsorption strength. This result indicates a heightened reactivity in forming C–N bonds via the CO2 + *N1 couplings. Our theoretical exploration adeptly bridges the discrepancies observed between earlier experimental and theoretical studies.