The electrocatalytic co-reduction of CO₂ and NO₃⁻ offers a sustainable route to urea synthesis, which would decrease reliance on the Haber-Bosch process. However, the efficiency of this co-reduction process hinges on the ability of an electrocatalyst to promote C–N coupling, which is strongly influenced by the geometry of the catalyst surface. In this study, we computationally investigate the role of metal catalyst facets—specifically, stepped (e.g., (211)) versus terraced (e.g., (100), (111)) surfaces—in governing the activity and selectivity of C–N coupling for urea synthesis. Using grand-canonical density functional theory (GC-DFT), we compare facet-dependent activity trends for silver and copper electrodes by analyzing the thermodynamics and kinetics of coupling between key C- (CO₂, CO) and N- (NO, NOH, NH) intermediates under applied potentials (−1.0 V to +1.0 V vs SHE), at pH=0. Our results demonstrate that C–N coupling activity is sensitive to the surface coordination and that (211) stepped surfaces exhibit superior C–N coupling activity compared to (111) and (100) terraces. Facet-dependent Brønsted-Evans-Polanyi (BEP) relations are observed, with both the reaction energies and activation barriers scaling linearly with the co-adsorption energies of C- and N-species, making it a descriptor in determining activity for the coupling of different intermediates. We elucidate the role of electrode potential in modulating these facet-dependent C–N coupling effects. By elucidating the role of electrode surface geometry and applied electrochemical potential in C–N coupling, this work addresses some knowledge gaps for the design of electrocatalysts tailored for sustainable urea production, paving the path for energy-efficient, environmentally friendly fertilizer synthesis.
