Designing high-performance catalysts for urea electrosynthesis: synergy between single atoms and BC3 monolayers†

Electrochemical reduction of CO to value-added urea, achieved by coupling with N₂, offers a promising strategy for simultaneously addressing energy and environmental crises. Herein, inspired by the concept of “single-atom (SA) and support co-catalysis,” where both the single atom and the support act as active catalytic sites, we designed a novel catalyst for urea electrosynthesis by anchoring single atoms onto a defective BC₃ monolayer. Due to the synergistic effect between the SA and adjacent B atoms in the support, two N₂ molecules can be chemisorbed and activated, allowing them to couple further with a CO molecule to form the ^*N₂CON₂^# intermediate, which can then be hydrogenated to produce urea without cleaving the inert N–N bond. Along this reaction pathway, our density functional theory computations identified Hf/BC₃ as the optimal catalyst for urea generation, exhibiting a low limiting potential (−0.47 V), a low C–N coupling energy barrier (0.62 eV), and strong suppression of competing reactions, resulting in excellent catalytic activity and selectivity. Furthermore, the d-band center of the anchored metal atoms and the p-band center of the adjacent B active sites explain the catalytic trends of different catalysts in urea synthesis. In particular, by utilizing the effective d electron number, electronegativity, and the sum between the d-band center of the metal and the p-band center of B as universal features, the novel descriptor was developed to assess the adsorption energy of ^*N₂CON₂^#. Our findings not only contribute an effective electrocatalyst for urea synthesis but also broaden the applications of single-atom and support co-catalysis, potentially inspiring future research into designing efficient co-catalysts for other electrocatalytic applications.