Electrocatalytic Urea Synthesis via C–N Coupling from CO₂ and Nitrogenous Species

Abstract

Metrics & MoreArticle Recommendations CONSPECTUS: Industrial urea synthesis consists of the Haber− Bosch process to produce ammonia and the subsequent Bosch− Meiser process to produce urea. Compared to the conventional energy-intensive urea synthetic protocol, electrocatalytic C−N coupling from CO 2 and nitrogenous species emerges as a promising alternative to construct a C−N bond under ambient conditions and to realize the direct synthesis of high-value urea products via skipping the intermediate step of ammonia production. The main challenges for electrocatalytic C−N coupling lie in the intrinsic inertness of molecules and the competition with parallel side reactions. In this Account, we give an overview of our recent progress toward electrocatalytic C−N coupling from CO 2 and nitrogenous species toward urea synthesis.To begin, we present the direct transformation of dinitrogen (N 2 ) to the C−N bond by coelectrolysis, verifying the feasibility of direct urea synthesis from N 2 and CO 2 under ambient conditions. In contrast to the highly endothermic step of proton coupling in conventional N 2 reduction, the N 2 activation and construction of the C−N bond arise from a thermodynamic spontaneous reaction between CO (derived from CO 2 reduction) and *N�N* (the asterisks represent the adsorption sites), and the crucial *NCON* species mediates the interconversion of N 2 , CO 2 , and urea. Based on theoretical guidance, the effect of N 2 adsorption configurations on C−N coupling is investigated on the model catalysts with defined active site structure, revealing that the side-on adsorption rather than the end-on one favors C−N coupling and urea synthesis. Electrocatalytic C−N coupling of CO 2 and nitrate (NO 3 − ) is also an effective pathway to achieve direct urea synthesis. We summarize our progress in the C−N coupling of CO 2 and NO 3 − , from the aspects of modulating intermediate species adsorption and reaction paths, monitoring irreversible and reversible reconstruction of active sites, and precisely constructing active sites to match activities and to boost the electrocatalytic urea synthesis. In each case, in situ electrochemical technologies and density functional theory (DFT) calculations are carried out to unveil the microscopic mechanisms for the promotion of C−N coupling and the enhancement of urea synthesis activity. In the last section, we put forward the limitations, challenges, and perspectives in these two coupling systems for further development of electrocatalytic urea synthesis.

Electrocatalytic C–N coupling for urea synthesis: a critical review

“…9b). 156,157 As another useful tool to reveal the presence/disappearance of the intermediates during the electrocatalytic processes, DEMS spectroscopy is promising for parsing the pathway of urea synthesis (Fig. 9f).…”

Advances in Catalysts for Urea Electrosynthesis Utilizing CO2 and Nitrogenous Materials: A Mechanistic Perspective

“…During the electrochemical synthesis of urea, improving the FE and AE of CO 2 and N 2 represents a significant challenge due to the high dissociation energy of chemical bonds and the limited solubility of reactant molecules in water [10][11][12]21,22]. A great body of work has already sought to address many of these limitations like exploring novel synthesis strategies to enhance the specific adsorption efficiency of reactants by introducing new active sites and optimizing catalyst morphology and structure to achieve superior catalytic performance [16,17,19,[22][23][24][25][26]. Researchers have optimized the structure of catalyst by fabricating porous electrodes, e.g., designing nanocrystalline materials, MXenes, to increase specific surface areas and active sites [19], thereby increasing the binding sites between the catalyst and reactants [23,24].…”

“…The improvement of the efficiency of urea production by overcoming the challenges of electrocatalytic urea synthesis has been a subject of intense interest [14]. At present, major challenges in electrocatalytic synthesis of urea include (i) highly stable chemical bond of N 2 and CO 2 , which requires specific catalyst for activation, (ii) low solubility of reactant molecular in water electrolyte, and (iii) parallel competitive reduction reactions resulting in low selectivity [1,4,[15][16][17].…”

Electrosynthesis of nitriles from primary alcohols and ammonia on Ni catalyst

“…Notable works in electrocatalytic C-N coupling include the electrosynthesis of amines and amides from CO2 or CO. [9][10][11] Interestingly, urea has been successfully synthesised from CO2 and various nitrogenous species. [12] Recently, the valorisation of CO2derived formic acid and methanol to formamide has also been demonstrated. [13][14][15] Biomass-derived carbonyl compounds are also used for the electrocatalytic reductive amination (ERA) C-N coupling reaction.…”