Facet Effects of Cu and Ag on C–N Coupling in CO ₂ –NO ₃ ^– Electroreduction

Electrocatalytic coreduction of carbon dioxide (CO2) and nitrate (NO3–) offers a sustainable route to the synthesis of urea. A major challenge for this reaction is enhancing C–N coupling, which is strongly influenced by catalyst composition and surface morphology. Here, we use grand-canonical density functional theory (GC-DFT) to model how the exposed facet of Ag and Cu electrodes affects the intrinsic kinetics of C–N coupling, comparing stepped (211) and terrace (100, 111) surfaces under applied electrochemical potentials in acidic media. We predict that low-coordination stepped surfaces (211) exhibit superior C–N coupling activity compared to terraces. Linear scaling relations link reaction energies and activation barriers with coadsorption energies for key C–N coupling steps with the coadsorption energies of C- and N-species, providing a thermodynamic descriptor for intermediate coupling. The potential-dependence origins of representative C–N coupling reactions are dominated by capacitive and dipole-field effects, which are larger for CO2 coupling than for CO coupling. These insights reveal why stepped sites are more active for the first C–N coupling step and may guide nanostructuring strategies to design electrocatalysts for CO2–NO3– coreduction.