Mechanistic Insights and Predictive Screening of M@C2N Catalysts for Urea Electrosynthesis from N2 and CO2

Abstract

Electrocatalytic urea synthesis via the co-reduction of N₂ and CO₂ 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≡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 C₂N (M@C₂N) to identify active and selective electrocatalysts for urea synthesis. Four mechanistic pathways; CO₂, OCOH, CO, and NCON, are systematically explored, revealing that the initial and final protonation steps of adsorbed N₂ are critical in determining catalytic performance. Among the candidates, Nb@C₂N, Mo@C₂N, and Re@C₂N 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 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 descriptor-driven strategy for the rational design of single-atom electrocatalysts for ambient urea synthesis.