Abstract

Electrocatalytic urea synthesis via the co-reduction of N<inf>2</inf> and CO<inf>2</inf> under ambient conditions offers a sustainable alternative to energy-intensive industrial processes. However, this process is hindered by several challenges, including the inertness of the N 00000000000000000 00000000000000000 00000000000000000 01111111111111110 00000000000000000 01111111111111110 00000000000000000 01111111111111110 00000000000000000 00000000000000000 00000000000000000 N bonds, sluggish C-N coupling kinetics, competing side reactions, and the lack of predictive models to guide catalyst development. In this study, we conduct a comprehensive density functional theory (DFT) screening of 26 transition metal single atoms anchored on graphitic C<inf>2</inf>N (M@C<inf>2</inf>N) to identify active and selective electrocatalysts for urea synthesis. Four mechanistic pathways, CO<inf>2</inf>, OCOH, CO, and NCON, are systematically explored, revealing that the initial and final protonation steps of adsorbed N<inf>2</inf> are critical in determining catalytic performance. Among the candidates, Nb@C<inf>2</inf>N, Mo@C<inf>2</inf>N, and Re@C<inf>2</inf>N exhibit the most favorable activity, achieving low limiting potentials of −0.50, −0.51, and −0.51 V, respectively. To accelerate catalyst discovery, we introduce a physically grounded descriptor, Φ, based on the d-electron count and electronegativity of the anchored metals, which accurately captures structure-activity relationships and enables rapid screening across materials. Our results establish a mechanistic framework and a descriptor-driven strategy for the rational design of single-atom electrocatalysts for ambient urea synthesis.