posted on 2023-12-14, 13:04authored byJunxian Liu, Xingshuai Lv, Yandong Ma, Sean C. Smith, YuanTong Gu, Liangzhi Kou
Electrocatalytic urea synthesis through N2 + CO2 coreduction 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
NN bonds for C–N coupling, competing side reactions,
and the absence of theoretical principles guiding catalyst design.
In this study, we propose a 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 NN 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
specific urea precursor *NNCONN* with both thermodynamic and kinetic
feasibility. Through the proposed 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, the electronegativity of the metal
atoms, and the generalized electronegativity of the substrate atoms,
making it potentially applicable to other urea catalysts. Our work
advances the comprehension of mechanisms and provides a universal
guiding principle for catalyst design in urea electrochemical synthesis.