Mo₂P Monolayer as a Superior Electrocatalyst for Urea Synthesis from Nitrogen and Carbon Dioxide Fixation: A Computational Study

Abstract

Urea synthesis through the simultaneous electrocatalytic reduction of N2 and CO2 molecules under ambient conditions holds great promises as a sustainable alternative to its industrial production, in which the development of stable, highly efficient, and highly selective catalysts to boost the chemisorption, activation, and coupling of inert N2 and CO2 molecules remains rather challenging. Herein, by means of density functional theory computations, we proposed a new class of two‐dimensional nanomaterials, namely, transition‐metal phosphide monolayers (TM2P, TM = Ti, Fe, Zr, Mo, and W), as the potential electrocatalysts for urea production. Our results showed that these TM2P materials exhibit outstanding stability and excellent metallic properties. Interestingly, the Mo2P monolayer was screened out as the best catalyst for urea synthesis due to its small kinetic energy barrier (0.35 eV) for C–N coupling, low limiting potential (−0.39 V), and significant suppressing effects on the competing side reactions. The outstanding catalytic activity of the Mo2P monolayer can be ascribed to its optimal adsorption strength with the key *NCON species due to its moderate positive charges on the Mo active sites. Our findings not only propose a novel catalyst with high‐efficiency and high‐selectivity for urea production but also further widen the potential applications of metal phosphides in electrocatalysis.

Electrocatalytic Urea Synthesis via N2 Dimerization and Universal Descriptor

“…Previous studies have identified the tower-like configuration of *NCON as a key reaction intermediate for the electrochemical urea synthesis. − ,,, However, the formation of C–N bonds faces challenges due to the sluggish nature of inserting *CO into the stable NN bond, which necessitates overcoming the strong bond energy of inert N 2 molecules. To solve the problem and increase the reaction efficiency, here we propose a mechanism for electrochemical urea formation from N 2 and CO. As shown in Figure a, the complete dual N 2 and CO coreduction process can be divided into three steps: (1) the adsorption and activation of two N 2 molecules on biactive sites, (2) the formation of the key *NNCONN* intermediate, and (3) the protonation of *NNCONN* to urea.…”

“…By utilizing dimerized *N 2 , CO can be embedded into two *N 2 molecules to achieve direct and concurrent N–C–N coupling, resulting in the formation of an intermediate, namely *NNCONN*. Compared to conventional C–N coupling processes that form the NCON precursor, ,,, the synchronous C–N coupling facilitated by *N 2 dimerization and CO eliminates the need for challenging N–N bond rupture and selective reduction of CO 2 to CO. Once *NNCONN* is formed, subsequent hydrogenation processes can generate ammonia and urea.…”

A comparative overview of the electrochemical valorization and incorporation of CO2 in industrially relevant compounds

“…Some extensive and purely theoretical reports modeling various catalytic systems for urea formation are also available and can be found elsewhere. [210][211][212][213][214][215][216][217] Understanding how the inert N 2 gets adsorbed and activated is paramount for rational design of an efficient catalyst. In general, a donor-acceptor process is operational, where the occupied s orbitals of N 2 donate electrons to the catalyst, which in turn donates electrons to the empty p* orbitals of N 2 , reducing the N-N bond order.…”

Urea Electrosynthesis Accelerated by Theoretical Simulations

“…Recently, Chen et al predicted a new class of 2D materials, namely, transition-metal phosphide monolayers (TM 2 P, TM = Ti, Fe, Zr, Mo, and W), as the potential electrocatalysts for urea production from coupling CO 2 and N 2 . [38] Based on the DFT calculations, a volcano curve between the catalytic activities (U L ) and the adsorption energies of *NCON species (ΔE *NCON ) is obtained. Either too strong (e.g., Zr 2 P and Ti 2 P) or too weak (e.g., Fe 2 P) binding strength of *NCON on TM 2 P monolayers leads to inadequate catalytic activity for urea production.…”