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.