Recent Progress in Electrocatalytic Urea Synthesis under Ambient Conditions

Abstract

Industrial urea synthesis is performed under harsh conditions requiring huge energy consumption and accompanied by heavy environmental pollution. Electrocatalytic C− N coupling for valuable urea synthesis from the coreduction of CO 2 and an inexpensive nitrogen source, such as N 2 , nitrite, nitrate, and NO, under ambient conditions is a potential green and sustainable substitute for the harsh industrial process. However, the nuts and bolts of electrocatalytic urea synthesis are seldom systemically reviewed. In this Perspective, theoretical and experimental research progress toward urea electrosynthesis is introduced and critically highlighted. From the view of the reaction pathway for the generation of urea molecules, chemiadsorption and activation of inert molecules (CO 2 or N 2 ) and the subsequent C−N couplings are the most important steps to determine the efficiency and selectivity of electrocatalytic reactions. The mechanisms of C−N coupling and hydrogenation toward urea formation in the above progress are summarized and rigorously estimated. This perspective reviews the exploration and preparation of electrocatalysts for urea synthesis with high efficiency and selectivity.

Electrochemical Co-reduction of N2 and CO2 to Urea Using Bi2S3 Nanorods Anchored to N-Doped Reduced Graphene Oxide

“…Finally, to further accurately detect the electrosynthesis of urea, the 1 H nuclear magnetic resonance ( 1 H NMR) method was used to analyze the urea generated after the reaction in the electrolyte. 57 As shown in Figure 5b, the 1 H NMR spectrum chemical shift at 5.6 ppm further verifies the production of urea originating from N 2 −CO 2 electrocoupling. Additionally, the integral area of 1 H NMR spectra is directly related to the urea content, and the quantitative calibration curve for various concentrations of urea is shown in Figure S12.…”

“…All of the results suggest that the Bi 2 S 3 /N-RGO composites exhibit high stability and durability for the electrosynthesis of urea. Finally, to further accurately detect the electrosynthesis of urea, the 1 H nuclear magnetic resonance ( 1 H NMR) method was used to analyze the urea generated after the reaction in the electrolyte . As shown in Figure b, the 1 H NMR spectrum chemical shift at 5.6 ppm further verifies the production of urea originating from N 2 –CO 2 electrocoupling.…”

Co-designing Electrocatalytic Systems with Separations To Improve the Sustainability of Reactive Nitrogen Management

“…Coupling renewably powered electrocatalytic methods with separation processes can provide a new avenue to sustainably close the nitrogen cycle. N r species have been electrocatalytically converted into not only inert N 2 but also value-added products such as ammonia, urea, hydroxylamine, and hydrazine under a wide variety of electrochemical conditions. ,, The applicability of such transformations to large-scale N r remediation is limited, however, by the generally dilute concentrations of N r in relevant feedstocks . At the same time, the separations research community has developed methods to remove and recover N r from waste streams into highly concentrated effluent streams. − Thus, there is a clear opportunity to couple electrocatalysis and separations in tandem to enable the simultaneous separation and remediation of N r pollutants into usable products.…”

“…N r species have been electrocatalytically converted into not only inert N 2 but also value-added products such as ammonia, urea, hydroxylamine, and hydrazine under a wide variety of electrochemical conditions. 6,26,27 The applicability of such transformations to large-scale N r remediation is limited, however, by the generally dilute concentrations of N r in relevant feedstocks. 27 At the same time, the separations research community has developed methods to remove and recover N r from waste streams into highly concentrated effluent streams.…”

Urea Electrosynthesis in Microbial Electrolysis Cells Using Low-cost Fe–N–C for Simultaneous N2 and CO2 Reduction

“…3−5 The electrocatalytic coupling of N 2 and CO 2 to form urea in aqueous systems is a potential green alternative to conventional industrial urea production. 6,7 This route requires only ambient temperature and pressure, and energy is supplied using clean and renewable resources. 8−10 In recent years, multiple researchers have focused on the design of high-performance catalysts for urea electrosynthesis.…”