Electrocatalytic Urea Synthesis via N2 Dimerization andUniversal Descriptor

This is the authors' abstract. We don't add key points for this paper.

Electrocatalytic urea synthesis through N2 + CO2 co-reduction and C−N coupling is a promising and sustainable alternative to harsh industrial processes. Despite considerable efforts, limited progress has been made due to the challenges of breaking inert N≡N bonds for C−N coupling, competing side reactions, and the absence of theoretical principles guiding catalyst design. In this study, we propose a new mechanism for highly electrocatalytic urea synthesis using two adsorbed N2 molecules and CO as nitrogen and carbon sources, respectively. This mechanism circumvents the challenging step of N≡N bond breaking and selective CO2 to CO reduction, as the free CO molecule inserts into dimerized *N2 and binds concurrently with two N atoms, forming a unique urea precursor *NNCONN* with both thermodynamic and kinetic feasibility. Through the new mechanism, Ti2@C4N3 and V2@C4N3 are identified as highly active catalysts for electrocatalytic urea formation, exhibiting low onset potentials of -0.741 and -0.738 V, respectively. Importantly, taking transition metal atoms anchored on porous graphite-like carbonitride (TM2@C4N3) as prototypes, we introduce a simple descriptor, namely, effective d electron number (Φ), to quantitatively describe the structure-activity relationships for urea formation. This descriptor incorporates inherent atomic properties of the catalyst, such as the number of d electrons, electronegativity of the metal atoms, and generalized electronegativity of the substrate atoms, making it potentially applicable to other urea catalysts. Our work advances novel mechanisms and provides a universal guiding principle for catalyst design in urea electrochemical synthesis.