Urea Electrosynthesis Accelerated by Theoretical Simulations

Abstract

Urea is not only a primary fertilizer in modern agriculture but also a crucial raw material for the chemical industry. In the past hundred years, the prevailing industrial synthesis of urea heavily relies on the Bosch–Meiser process to couple NH3 and CO2 under harsh conditions, resulting in high carbon emissions and energy consumption. The conversion of carbon‐ and nitrogen‐containing species into urea through electrochemical reactions under ambient conditions represents a sustainable strategy. Despite the increasing reports on urea electrosynthesis, a comprehensive review that delves into a profound, atomic‐level comprehension of the fundamental reaction mechanisms is currently absent. In this Perspective, recent advancements in electrochemical urea synthesis from CO2/CO and various nitrogenous species (i.e., N2, NOx−, and NO) under ambient conditions are presented, with special emphasis on theoretical understanding of the C─N coupling reaction mechanisms. Several key strategies to facilitate the C─N coupling are then pinpointed, which not only enhance their applicability in practical experiments but also highlight the significant progress achieved in this field. At the end, the major obstacles and potential opportunities in advancing urea electrosynthesis accelerated by theoretical simulations and in situ techniques are discussed. This review is hoped to act as a roadmap to ignite fresh insights and inspiration for the development of electrocatalytic urea synthesis.

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].…”

Electrochemical urea production using carbon dioxide and nitrate: state of the art and perspectives

“…Both mechanisms lead eventually to the hydrogenation of the adsorbed intermediate and subsequent combination with another adsorbed species followed by reduction to form eventually CO(NH 2 ) 2 . 30–32…”

“…18 Remarkably, to date, to our best knowledge, only a scant few studies (around 21) have been published in the past three years related to urea electrosynthesis starting from NO 3 − and CO 2 . 29–52 These manuscripts provide a solid starting point for the research, but fundamental investigations are needed to clarify the steps that determine the most activity and selectivity: no direct experimental evidence has yet been reported showing the formation of intermediate species, but many DFT studies suggest that that pathway is energetically favourable for the formation of urea, at least on some electrocatalytic structures. For example Sargent et al showed by DFT calculation that the pathway seems to be favoured on Zn, rather than on Cu, in a ZnCu electrocatalyst.…”

“…Ideally, an efficient electrocatalyst should promote C–N coupling while restricting or suppressing the side reactions, including hydrogen evolution, 72,85,86 carbon dioxide reduction 87 and nitrate reduction reactions. 30 However, it is not yet clear which family of electrocatalysts is the most selective for urea electrosynthesis from the perspective of the aforementioned considerations. Nevertheless, recent scientific endeavors on a variety of electrocatalysts including transition metal-based, single-atom, heteroatomic and bimetallic systems are intuitive, but still rational design and proper benchmarking are primarily missing.…”