Linking CO to Urea Production from CO<sub>2</sub> and NO<sub>3</sub><sup>–</sup>/NO<sub>2</sub><sup>–</sup> Co-Electrolysis on Transition Metals
Hsien-Chin Li, Yeu‐Shiuan Ho, Guo-Lin Yang, Ren-Han Li, Tung‐Chun Kuo, Chi-Tien Hsieh, Youngkook Kwon, Mu‐Jeng Cheng
Abstract
Electrochemical reduction of CO 2 (CO 2 ER) has the potential to advance carbon neutrality and renewable energy storage. Advanced CO 2 ER catalysts can selectively produce a wide array of products. Their importance is amplified when coreducing CO 2 with nitrate/nitrite ions (NO 3 – /NO 2 – ) to generate organic compounds containing C–N bonds, enhancing product diversity and value. Some transition metals effectively catalyze the coreduction of CO 2 and NO 3 – /NO 2 – 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 CO 2 + *N 1 (the intermediates from NO 3 – /NO 2 – reduction to NH 3 ) 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, *N 1, 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 CO 2 ER is indicative of its reduced adsorption strength. This result indicates a heightened reactivity in forming C–N bonds via the CO 2 + *N 1 couplings. Our theoretical exploration adeptly bridges the discrepancies observed between earlier experimental and theoretical studies.