Electrochemical C-N coupling of CO2 and nitrogenous small molecules for the electrosynthesis of organonitrogen compounds

Advances in the Structure-Activity Relationship of Electrocatalytic C-N Coupling: From Nanocatalysis to Single Metal Site Catalysis

C-N coupling is crucial for constructing amides and amines and involves various fields, including medicine, chemical industries, agriculture, and energy. With the rapid development of electrocatalytic C-N coupling and the continuous improvement of catalytic performance, this field has aroused extensive research interest. A comprehensive review is urgently needed to summarize the structure-activity relationship, key challenges, and future development directions. This review provides a concise overview of the recent advancements from nanocatalysis to single metal site catalysis for electrocatalytic C-N coupling reactions. We summarize the C-N coupling mechanisms using different nitrogen sources and further analyze the influences of various active metal centers and different coordination environments on the C-N coupling performance, thereby elucidating the structure-activity relationship. Moreover, we discuss the dynamic structural evolution of active metal sites during the reaction. Finally, we present current challenges and perspectives in this field. This review aims to provide valuable insights into the development of advanced nano/single metal site catalysts for electrocatalytic C-N coupling reactions along with a deeper understanding of catalytic mechanisms.

Theory-Guide Design of Integrative Catalytic Pairs for Urea Synthesis from Nitrate and Carbon Dioxide

Electrochemical coreduction of carbon dioxide and nitrate offers a sustainable pathway to synthesize value-added urea from greenhouse gas and nitrogen-containing waste; however, challenges remain in designing efficient catalysts. Based on the concept of "integrative catalytic pairs (ICPs)", a catalyst for urea synthesis is designed by introducing heteroatoms (B and C) into M-N-C, where a single transition metal is dispersed on N-doped carbon material. Using a two-step theoretical screening strategy, Ni-N3B is identified as a promising catalyst for urea synthesis, with a low limiting potential (-0.43 V) and a small kinetic barrier for C-N coupling (0.74 eV) due to the electronic regulation effects and the synergy of Ni and B function for enhancing NO3- activation and facilitating C-N coupling between gaseous CO2 and *NH intermediate. Under the guidance of these theoretical results, our further experimental validation demonstrates that the synthesized Ni-N3B catalyst achieves a Faradaic efficiency of 51.92% and a urea yield rate of 32.30 mmol h-1 g-1 at -0.6 V vs RHE. Our work not only identifies an efficient urea synthesis catalyst without relying on trial-and-error methods but also inspires further exploration of ICPs-based catalysts in electrocatalysis.

Cathode-Anode Synergy Electrosynthesis of Propanamide via a Bipolar C-N Coupling Reaction

Propanamide is a crucial synthetic intermediate in pharmaceuticals for the preparation of antibacterial and anticancer drugs. Conventional synthesis of propanamide involves the reaction of carboxylic acid derivatives with amines, which requires harsh reaction conditions, leading to an unfavorable environmental footprint. Here, we present a cathode-anode synergistic electrochemical strategy to transform nitrate and n-propanol into propanamide under ambient conditions, where both the cathode catalyst Co3O4/SiC and the anode catalyst Ti contribute distinctively to the electrochemical process. The CH3CH2CHO produced at the Ti anode can diffuse and react with the adsorbed intermediate *NH2OH on the surface of the cathode catalyst to form propanamide. The synergistic reactions at both electrodes collectively enhance the efficiency of the propanamide synthesis. This design enables efficient propanamide production in a flow cell at the gram scale with a remarkable yield of 986.13 μmol/(cm2·h) at current densities of up to 650 mA/cm2. Our reports present a new option for environmentally friendly C-N bond synthesis, and the insights can be useful for the electrosynthesis of a wider scope of amides.

Engineered Spatial Confinement of Cu Single-Atoms with Diagonal N─Cu─N Motifs for High-Rate CO2 Methanation

The renewable-electricity-powered carbon dioxide reduction (eCO2R) to value-added fuels and feedstocks like methane (CH4) holds the sustainable and economically viable carbon cycle at meaningful scales. However, this kinetically challenging eight-electron multistep deep-reduction encounters insufficient catalyst design principles to steer complex CO2 reduction pathways. Utilizing atomic copper (Cu) structures with unitary active sites can boost eCO2R-to-CH4 selectivity due to the efficient suppression of unwanted C─C coupling. Herein, we report a sequential ion exchange strategy to fabricate periodic Cu single-atom catalysts within a polymeric carbon nitride (PCN) matrix, where the uniformly dispersed, diagonally coordinated N─Cu─N configuration hosts low-valent Cuδ+ centers. Leveraging the periodic N-anchoring sites with delocalized π-electron conjugation in the PCN matrix, the isolated Cu sites are obtained with an interatomic distance of ∼4.2 Å under high metal-loading conditions. This engineered spatial configuration effectively inhibits C─C coupling to avoid subsequent multicarbon product formation. The optimized Cu1/PCN demonstrates exceptional eCO2R-to-CH4 performance, achieving 71.1% CH4 Faradaic efficiency with a high partial current density of 426.6 mA cm-2 at -1.50 V versus reversible hydrogen electrode, outpacing the state-of-the-art catalysts. This work delves into effective concepts for steering desirable reaction pathways via precisely modulating active site structures at the atomic level to create favorable microenvironments.

TEMPO-Mediated Electrochemical α-Allylation of Tetrahydroisoquinolines

A C(sp3)-H allylation of tetrahydroisoquinolines has been developed by combining Shono oxidation with a vinylogous Mannich-type reaction. TEMPO was used as the electrocatalyst to lower the electrode potential, improving functional group compatibility. This method provided a practical and efficient tandem procedure for the α-allylation of tetrahydroisoquinolines. The reaction proceeded through the formation of an iminium cation intermediate, which was generated in situ by anodic oxidation, followed by nucleophilic addition of 2-allylazaarenes.

Valorizing Nitrate in Electrochemical Nitrogen Cycling: Copper-Based Catalysts from Reduction to C-N Coupling

Electrochemical nitrate reduction (NO3RR) offers a sustainable approach to mitigating nitrogen pollution while enabling the resourceful conversion of nitrate (NO3 -) into ammonia (NH3), nitrogen gas (N2), and value-added chemicals such as urea. Copper (Cu)-based catalysts, with their versatile catalytic properties and cost-effectiveness, have emerged as pivotal materials in advancing NO3RR. This review systematically summarizes recent progress in Cu-based catalysts for NO3RR, focusing on their catalytic mechanisms, tuning strategies, and applications across diverse product pathways. The intrinsic self-reconstruction behavior and synergistic effects of Cu-based catalysts are elucidated alongside advanced in situ characterization techniques that reveal dynamic structural evolution and intermediate interactions during reactions. We comprehensively discuss the performance of Cu-based catalysts in steering NO3RR toward NH3 or N2 production, emphasizing the role of catalyst design (e.g., single atoms, alloys, oxides, hydroxides) in enhancing selectivity and efficiency. Furthermore, the multifunctionality of Cu catalysts is exemplified through carbon-nitrogen (C-N) coupling reactions, where reactive nitrogen intermediates are valorized into urea. Key challenges and future directions are outlined to guide the rational design of Cu-based systems for efficient electrochemical nitrogen cycling.

Photocatalytic C-N coupling from stable and transient intermediates for gram-scale acetamide synthesis

Electro/photocatalytic C-N coupling acts as a key build-block to the next generation of chemicals like amides for wide applications in energy, pharmaceuticals and chemical industries. However, the uncontrolled intermediates coupling challenges the efficient amide production regarding yield or selectivity. Here we propose a photocatalytic radical addition route, where the fundamental active species, including oxygen and photogenerated electron-hole pairs, are regulated for selective intermediates generation and efficient acetamide synthesis from mild co-oxidation of CH3CH2OH and NH3. Sufficient CH3CH2OH is provided to accumulate the stable intermediate (CH3CHO). Meanwhile, the limited NH3 concentration ensures the controllable generation and fast addition of the transient radical (●NH2) on CH3CHO. Through the directed coupling of stable-transient intermediates, the acetamide synthesis rate is pushed forward to a hundred-mmol level (105.61 ± 4.86 mmol·gcat-1·h-1) with a selectivity of 99.17% ± 0.39%, reaching a gram-scale yield (1.82 g) of acetamide. These results illuminate valuable opportunities for the photocatalysis-driven synthetic industry.

Electrocatalytic N-C-N coupling over a hierarchically ordered open single-atom superstructure toward organonitrogen synthesis

Electrochemically constructing C-N and N-C-N bonds provides an economical and sustainable alternative to conventional chemosynthesis. Herein, a hierarchically ordered open superstructure of N-doped carbon isolated with accessible three-coordinated Zn single-atom sites is explored for efficient electrocatalytic N-C-N coupling. Benefiting from the distinctive structural merits, this catalyst enables electrocatalytic preparation of N-C-N bonded compounds from methanol and amines. Notably, the Faradaic efficiency and selectivity of N,N,N',N'-tetramethyldiaminomethane reach up to 77% and 96% at 0.8 V, respectively. Further integrating the aminoalkylation reaction, an electro-thermo cascade synthesis is explored with the electrochemically obtained N,N,N',N'-tetramethyldiaminomethane serving as a unique reagent, leading to a specific set of organonitrogen compounds with (dimethylamino)methyl substituent, including topotecan hydrochloride, an anti-tumor drug, with a high yield of 95%. Furthermore, the in situ spectroscopic characterization and calculations unveil that the under-coordinated Zn-N3 sites play a pivotal role in stabilizing the key *CH2O intermediate, thereby facilitating subsequent nucleophilic addition with amines.

Electrochemical Amination of Aryl Halides with NH3

Primary arylamines are the most pivotal class of organic motifs in pharmaceuticals, agrochemicals, ligands and natural products. Ammonia (NH3) is an ideal nitrogen source in terms of reactivity, atom economy, and environmental compatibility. Despite significant progress in the synthesis of primary arylamines, the development of a general method for rapid access to diversely functionalized primary arylamines is still urgent and necessary. Herein, we developed a method for the direct synthesis of primary arylamines through electrochemical amination of aryl halides with NH3. Notably, the weak nucleophilic reagent NH3 was directly used as an ammonia surrogate, allowing for efficient conversion of carbon-halogen bonds to diverse primary arylamines with good functional group tolerance. A broad scope of functionalized primary arylamines has been achieved in moderate to excellent yields.

Electrosynthesis of Urea on High-Density Ga─Y Dual-Atom Catalyst via Cross-Tuning

Electrochemically converting carbon dioxide (CO2) and nitrate (NO3 -) into urea via the C─N coupling route offers a sustainable alternative to the traditional industrial urea production technology, but it is still limited by poor yield rate, low Faradaic efficiency, and insufficient coupling kinetics. Herein, a high-density Ga─Y dual-atom catalyst is developed with loading up to 14.1 wt.% of Ga and Y supported on N, P-co-doped carbon substrate (Ga/Y-CNP) for urea electrosynthesis. The catalyst facilitates efficient C─N coupling through co-reduction of CO2 and NO3 -, resulting in a high urea yield rate of 41.9 mmol h-1 g-1 and a Faradaic efficiency of 22.1% at -1.4 V versus the reversible hydrogen electrode. In situ spectroscopy and theoretical calculations reveal that the superior performance is attributed to the cross-tuning between adjacent pair Ga─Y sites, which can mutually optimize their electronic states for facilitating CO2 reduction to *CO at Ga sites and promoting NO3 - conversion to hydroxylamine (*NH2OH) at Y sites, followed by spontaneous coupling of *CO and *NH2OH intermediates at Ga─Y sites to form C─N bonds. This work offers a pioneering strategy to manipulate C─N coupling pathways by cross-tuning active sites to produce high-value-added chemicals.

Bifunctional transition-metal catalysts for energy-saving hydrogen generation from nitrogenous wastewater

Wastewater from industrial chemical synthesis, agricultural activities, and domestic sewage usually contains high levels of nitrogenous compounds, endangering environmental health and human well-being. Nitrogenous wastewater electrolysis (NWE), despite its ecological merits, is inherently hampered by sluggish kinetics. To improve process efficiency, lower costs, and avoid cross-contamination between the anode and cathode, a range of bifunctional transition-metal catalysts capable of efficient operation at both electrodes have recently been developed. This review outlines the progress in these catalysts for the energy-saving production of hydrogen from nitrogenous wastewater, including urea, hydrazine, and ammonia. It highlights their dual role in both degrading nitrogenous pollutants and generating hydrogen energy. The review meticulously introduces the key performance metrics of the NWE system and surveys the latest advancements in bifunctional transition-metal catalysts, along with their catalytic mechanisms. It culminates in a detailed summary and comparative analysis of representative bifunctional catalysts, emphasizing their electricity consumption and energy-saving efficiency. Lastly, the existing challenges and research prospects are thoroughly discussed.

Electrocatalytic Reductive Amination of Aldehydes and Ketones with Aqueous Nitrite

The electrocatalytic utilization of oxidized nitrogen waste for C-N coupling chemistry is an exciting research area with great potential to be adopted as a sustainable method for generation of organonitrogen molecules. The most widely used C-N coupling reaction is reductive amination. In this work, we develop an alternative electrochemical reductive amination reaction that can proceed in neutral aqueous electrolyte with nitrite as the nitrogenous reactant and via an oxime intermediate. We develop a selection criterion for nitrite reduction electrocatalysts suited for oxime electrosynthesis and, in doing so, find Pd to be a highly efficient catalyst for this reaction, reaching an oxime Faradaic efficiency of 82% at -0.21 V vs the reversible hydrogen electrode. The aliphatic or aromatic structure of the carbonyl reactant impacts the efficacy of the catalyst, with aromatic substrates leading to suppressed oxime formation and detrimental reduction of the carbonyl to the alcohol. We developed a Pb/PbO electrocatalyst that selectively performs oxime reduction in the neutral aqueous electrolyte. With acetone as a model substrate, we demonstrate an efficient one-pot, two-step electrochemical reaction for the conversion of acetone to isopropyl amine with 85% yield and 50% global Faradaic efficiency.

Clusters induced electronic delocalization of single atom sites toward efficient electrocatalytic urea synthesis from CO2 and N2

Electrocatalytic conversion of CO2 and N2 into urea product is highly envisaged, whereas symmetrical electronic architecture of inert reactant severely prevents their adsorption and activation and further entail extremely low intrinsic activity. Herein, a novel electrocatalyst consisting of Co clusters and CoN3 single-atoms dispersed on a carbon matrix is demonstrated to achieve the highest recorded urea yield rate of 20.83 mmol h-1 g-1 and Faradaic efficiency (FE) of 23.73 % at -0.4 V vs. RHE. Detailed investigations reveal that the concerted interplay between Co atomic clusters (CoAC) and plane-asymmetric Co-N3 single atom sites in CoN3-CoAC/NC specimen readily induced the unique electron delocalization effects and further prompted the orbital spin state of Co sites evolved from 3d74s1 to 3d84s0, which optimized the adsorption configuration of the reactants, polarized the gas molecules through interaction with the bonding and antibonding orbitals of the optimized catalysts and eventually lowered the CN coupling barriers to produce the desired urea product.

Tailoring Activation Intermediates of CO2 Initiates C-N Coupling for Highly Selective Urea Electrosynthesis

Electrocatalyzed reduction of CO2 and NO3- to synthesize urea is a highly desirable, but challenging reaction. The bottleneck of this reaction is the C-N coupling of CO2 and NO3- reduction intermediates. In particular, the uncertainty of CO2 multielectron reduction intermediates severely affects the selectivity and activity of C-N coupling processes involving multiple electron and proton transfers. Here, we present a novel tandem catalyst with two compatible single-atom active sites of Au and Cu on red phosphorus (RP-AuCu) that efficiently converts CO2 and NO3- to urea. Experimental and theoretical prediction results confirmed that the active center of Au on red phosphorus promotes electron transfer between CO2 molecules and red phosphorus, thereby regulating CO2 activation intermediates to produce electrophilic *COOH. In addition, the active center of Cu on red phosphorus can enhance the electrophilic attack of *COOH species on *NH2, thus promoting the selective formation of C-N bonds. Consequently, RP-AuCu exhibited a urea yield of 22.9 mmol gcat.-1 h-1 and a Faraday efficiency of 88.5% (-0.6 VRHE), representing one of the highest levels of electrocatalytic urea synthesis. This work deepens the understanding of the C-N coupling mechanism and provides an interesting catalyst design approach for the efficient and sustainable production of C-N compounds.

Dual Activation of N2 and CO2 toward N-O Coupling by Single Copper Ions

Concurrent activation and conversion of N2 and CO2 are of significance yet face numerous obstacles due to the large dissociation energies of N≡N and C═O bonds. Utilizing a specifically developed reflectron time-of-flight mass spectrometer, we investigated the dual activation of N2 and CO2 mediated by copper and silver ions under ambient conditions. Isotope experiments identified that both N2 and CO2 can be effectively activated to generate a N-O coupling product (NO+), especially in the presence of copper ions, and the NO+ product attains the maximum intensity with an N2/CO2 ratio of 1:2, which validates a three-molecule reaction mechanism, namely, N2 + 2CO2 → 2NO + 2CO. Through detailed analyses of thermo-dynamics and reaction dynamics, we illustrate the Cu+-catalyzed three-molecule reaction mechanism for N-O coupling, validating the dual activation of N2 and CO2 simply by plasma-assisted single-ion catalysis.

Spin State Modulation with Oxygen Vacancy Orientates C/N Intermediates for Urea Electrosynthesis of Ultrahigh Efficiency

The co-electrolysis of CO2 and NO3 - to synthesize urea has become an effective pathway to alternate the conventional Bosch-Meiser process, while the complexity of C-/N-containing intermediates for C-N coupling results in the urea electrosynthesis of unsatisfactory efficiency. In this work, an electronic spin state modulation maneuver with oxygen vacancies (Ov) is unveiled to effectively meliorate the oriented generation of key intermediates *NH2 and *CO for C-N coupling, furnishing urea in ultrahigh yield of 2175.47 µg mg-1 h-1 and Faraday efficiency of 70.1%. Mechanistic studies expound that Ov can induce the conversion of the high-spin state Ni2+ (t2g 6eg 2) of Ni@CeO2-x to the low-spin state Ni3+ (t2g 6eg 1), which markedly enhances the hybridization degree of the Ni 3d and the N 2p orbitals of *NO, facilitating the selective formation of *NH2. Notably, the in situ generated *NH2 intermediates can serve as a localized proton donor to promote the electroreduction of CO2 on the adjacent site Ce3+-O to exclusively afford *CO, followed by C-N coupling of each other to efficiently synthesize urea. The strategy of tailored switching of the active site spin state provides a reliable reference to rectify the electronic structure of electrocatalysts for directional CO2 valorization.

Quaternary Medium-Entropy Alloy Metallene with Strong Charge Polarization for Highly Selective Urea Electrosynthesis from Carbon Dioxide and Nitrate

Electrochemical urea synthesis via the coreduction of CO2 and NO3- is a sustainable alternative to the traditional Bosch-Meiser process. However, the sluggish reaction kinetics usually result in a low efficiency. Herein, we designed a kind of quaternary PdCuCoZn medium-entropy alloy (MEA) metallene for highly selective urea electrosynthesis. The random occupation of Cu, Co, and Zn with lower electronegativity in the face-centered cubic lattice of Pd-based metallene enables abundant electron donation from transition metals to adjacent Pd atoms, leading to the formation of charge-polarized Pdδ--Cu/Co/Znδ+ sites. Considering that the pivotal C- and N-intermediates, namely, *CO and *NH2, are electrophilic and nucleophilic, respectively, such strong charge polarization would greatly benefit their respective formation and stabilization. The stable adsorption with *CO bonded to electron-rich Pd-based sites and *NH2 bonded to electron-deficient Cu/Co/Zn-based sites is demonstrated by the combination of in situ characterizations and theoretical calculations. The proof-of-concept PdCuCoZn MEA metallene achieves a maximum urea yield rate of 1840 μg h-1 mg-1 and a high Faradaic efficiency of 70.2%, surpassing most of the reported state-of-the-arts. Our strategy proposed in this work is believed to enlighten the design of an effective catalyst used for multistep reactions.

Electrosynthesis of Organonitrogen Compounds via Hydroxylamine-Mediated Cascade Reactions

Hydroxylamine (NH2OH) is a key intermediate in the formation of numerous high value-added organonitrogen compounds. The traditional synthesis of NH2OH requires the use of precious metals under high temperature conditions, which leads to high cost, high energy consumption, and environmental pollution. The NH2OH-mediated cascade reaction integrates the electrochemical synthesis of NH2OH and the chemical synthesis of organonitrogen compounds, offering a facile, green, and efficient alternative. This review presents the recent advances on electrosynthesis of high value-added organonitrogen compounds by NH2OH-mediated cascade reactions. We present key concepts and the transformation process of different N-species to NH2OH, discuss suitable substrates and electrocatalysts, and elucidate the reaction mechanisms involved in generating compounds such as amino acids, cyclohexanone oxime, urea, amine, etc.. Finally, we address current challenges and future directions in this emerging field to encourage further research effort and the development of NH2OH-mediated cascade reaction.

Predicting electrocatalytic urea synthesis using a two-dimensional descriptor

Electrochemical synthesis routes powered by renewable electricity can provide sustainable chemical commodities by replacing conventional fossil-based processes. Increasing research focuses on value-added chemicals like the indispensable fertilizer urea, which also constitutes a study case for electrochemical CN-coupling. To guide the identification of highly selective catalysts, we aim to provide new insight by analysing existing experimental data on the selectivity of transition metal catalysts towards electrochemically synthesized urea. Firstly, we project high dimensional experimental data using principal component analysis (PCA) to lower dimensions, and thereby confirm that urea selectivity is correlated with the selectivity towards CO and NH3. Furthermore, we identified the most suitable two-dimensional descriptors for selectivity prediction out of various adsorption energies calculated using density functional theory (DFT). We suggest that the adsorption energies of *H and *O on transition metal slabs predict the selectivity towards urea in the co-reduction of CO2 and nitrite (NO 2 - ).

Promotion of C─C Coupling in the CO2 Electrochemical Reduction to Valuable C2+ Products: From Micro-Foundation to Macro-Application

The electrochemical CO2 reduction reaction (CO2RR) to valuable C2+ products emerges as a promising strategy for converting intermittent renewable energy into high-energy-density fuels and feedstock. Leveraging its substantial commercial potential and compatibility with existing energy infrastructure, the electrochemical conversion of CO2 into multicarbon hydrocarbons and oxygenates (C2+) holds great industrial promise. However, the process is hampered by complex multielectron-proton transfer reactions and difficulties in reactant activation, posing significant thermodynamic and kinetic barriers to the commercialization of C2+ production. Addressing these barriers necessitates a comprehensive approach encompassing multiple facets, including the effective control of C─C coupling in industrial electrolyzers using efficient catalysts in optimized local environments. This review delves into the advancements and outstanding challenges spanning from the microcosmic to macroscopic scales, including the design of nanocatalysts, optimization of the microenvironment, and the development of macroscopic electrolyzers. By elucidating the influence of the local electrolyte environment, and exploring the design of potential industrial flow cells, guidelines are provided for future research aimed at promoting C─C coupling, thereby bridging microscopic insights and macroscopic applications in the field of CO2 electroreduction.

Efficient urea electrosynthesis from CO2 and nitrate on amorphous TiS2

Electrosynthesis of urea via co-electrolysis of CO2 and NO3- (EUCN) offers a promising avenue for simultaneously addressing environmental concerns and producing valuable urea. In this study, we report that amorphous TiS2 (a-TiS2) with rich S-vacancies (Sv) serves as an effective and robust EUCN catalyst. In a flow electrolyzer, a-TiS2 achieves the maximum urea-Faradaic efficiency of 34.5 % and urea yield rate of 30.6mmol h-1 gcat-1 at -0.7 V. RHE, significantly outperforming crystalline TiS2 and most reported EUCN catalysts. A combination of extensive atomic characterizations, theoretical computations and in situ spectroscopic measurements reveals the synergistic catalysis of Ti site and Ti-Sv site to promote *NH2/*CO formation and their CN coupling, whilst suppressing the competing hydrogen evolution and NO3--to-NH3 reactions, thus enabling a highly selective EUCN for urea synthesis.

Purification and Value-Added Conversion of NOx under Ambient Conditions with Photo-/Electrocatalysis Technology

As primary air pollutants from fossil fuel combustion, the excess emission of nitric oxides (NOx) results in a series of atmospheric environmental issues. Although the selective catalytic reduction technology has been confirmed to be effective for NOx removal, green purification and value-added conversion of NOx under ambient conditions are still facing great challenges, especially for nitrogen resource recovery. To address that, photo-/electrocatalysis technology offers sustainable routes for efficient NOx purification and upcycling under ambient temperature and pressure, which has received considerable attention from scientific communities. In this review, recent advances in photo-/electrocatalysis technology for the purification and value-added conversion of NOx are critically summarized. The target products and reaction mechanisms for NOx conversion systems, together with the responsible active sites, are discussed, respectively. Then, the realistic environmental practicability is proposed, including strict performance evaluation criteria and application in realistic conditions for NOx purification and upcycling by the application of photo-/electrocatalysis. Finally, the current challenges and future opportunities are proposed in terms of catalyst design, NOx conversion enhancement, reaction mechanism understanding, practical application conditions, and product separation techniques.

Advanced systems for enhanced CO2 electroreduction

Carbon dioxide (CO2) electroreduction has extraordinary significance in curbing CO2 emissions while simultaneously producing value-added chemicals with economic and environmental benefits. In recent years, breakthroughs in designing catalysts, optimizing intrinsic activity, developing reactors, and elucidating reaction mechanisms have continuously driven the advancement of CO2 electroreduction. However, the industrialization of CO2 electroreduction remains a challenging task, with high energy consumption, high costs, limited reaction products, and restricted application scenarios being the issues that urgently need to be addressed. To accelerate the progress of CO2 electroreduction towards practical application, this review shifts the research focus from catalysts to aspects such as reactions and systems, aiming to improve reaction efficiency, reduce technical costs, expand the range of products, and enhance selectivity, offering readers a new perspective. In particular, innovative and specific design strategies such as CO2 reduction coupled with alternative oxidation, co-reduction reaction of CO2 and C/N/O/S-containing species, cascade systems, and integrated CO2 capture and reduction systems are discussed in detail. Additionally, personal views on the opportunities and future challenges of the aforementioned innovative strategies are provided, offering new insights for the future research and development of CO2 electroreduction.

Optimizing cooperative catalysis of multiple defective interfaces in Pt/mullite catalysts for NO oxidation

Nitric oxide (NO) oxidation is an integral part of the nitrogen chemical cycle, but competitive activation of NO/O2 over single platinum (Pt)-based catalysts result in inadequate low temperature performance. Here, we constructed catalysts with BiMn2O5/CeO2 and Pt/BiMn2O5 defective interfaces (sufficient activation of NO/O2). The constructed catalyst achieved 95 % NO conversion at 260 °C in NO/O2 atmosphere, superior to most known catalysts. Even after aging (800 °C for 16 h), the NO conversion was up to 76 %. Further, the catalyst can be applied to actual diesel exhaust. Detailed oxygen vacancies (Ov) characterization reveals that BiMn2O5/CeO2 defective interface created by Ce3+-Ov + Mn4+-O ↔ Ce4+-O + Mn3+-Ov promote the activation of NO (on Mn3+ sites) and O2 (on Mn3+-Ov sites). Besides, the Ov on Pt/BiMn2O5 defective interface compensate for the loss of Pt sites ensuring hydrothermal stability. And this construction of multiple defective interfaces develops a pathway for boosting catalytic reactions.

Rectifying Heterointerface Facilitated C-N Coupling Dynamics Enables Efficient Urea Electrosynthesis Under Ultralow Potentials

Electrocatalytic C-N coupling for urea synthesis from carbon dioxide (CO2) and nitrate (NO3 -) offers a sustainable alternative to the traditional Bosch-Meiser method. However, the complexity of intermediates in co-reduction hampers simultaneous improvement in urea yield and Faradaic efficiency (FE). Herein, we developed a Cu/Cu2O Mott-Schottky catalyst with nanoscale rectifying heterointerfaces through precise controllable in situ electroreduction of Cu2O nanowires, achieving notable FE (32.6-47.0 %) and substantial yields (6.08-30.4 μmol h-1 cm-2) across a broad range of ultralow applied potentials (0 to -0.3 V vs. RHE). Operando synchrotron radiation-Fourier transform infrared spectroscopy (SR-FTIR) confirmed the formation of *CO intermediates and C-N bonds, subsequently density functional theory (DFT) calculations deciphered that the Cu/Cu2O rectifying heterointerface modulated *CO adsorption, significantly enhancing subsequent C-N coupling dynamics between *CO and *NOH intermediates. This work not only provides a groundbreaking and advanced pathway for C-N coupling, but also offers deep insights into copper-based heterointerface catalysts for urea synthesis.

Solid-Liquid-Gas Three-Phase Indirect Electrolysis Enabled by Affinity Auxiliary Imparted Covalent Organic Frameworks

The design of efficient heterogeneous redox mediators with favorable affinity to substrate and electrolyte are much desired yet still challenging for the development of indirect electrolysis system. Herein, for the first time, we have developed a solid-liquid-gas three-phase indirect electrolysis system based on a covalent organic framework (Dha-COF-Cu) as heterogeneous redox mediator for S-S coupling reaction. Dha-COF-Cu with the integration of high porosity, nanorod morphology, abundant hydroxyl groups and active Cu sites is much beneficial for the adsorption/activation of thiols, uniform dispersion and high wettability in electrolyte, and efficient interfacial electron transfer. Notably, Dha-COF-Cu as solid-phase redox mediator exhibits excellent electrocatalytic efficiency for the formation of value-added liquid-phase S-S bond product (yields up to 99 %) coupling with the generation of gas-phase product of H2 (~1.40 mmol g-1 h-1), resulting in a powerful three-phase indirect electrolysis system. This is the first work about COFs that can be applied in three-phase indirect electrolysis system, which might promote the development of porous crystalline materials in this field.

Total Electrosynthesis of N, N-Dimethylformamide From CO2 and NO3. ADVANCED SCIENCE (WEINHEIM, BADEN-WURTTEMBERG, GERMANY) 2025;12:e2414431. [PMID: 39573891 PMCID: PMC11727272 DOI: 10.1002/advs.202414431] [Citation(s) in RCA: 0] [Impact Index Per Article: 0]

Electrochemical C-N coupling presents a promising strategy for converting abundant small molecules like CO2 and NO3 - to produce low-carbon-intensity chemicals in a potentially more sustainable route. A prominent challenge is the limited product scope, particularly for organonitrogen chemicals featuring a variety of functional groups, alongside the limited understanding of plausible reaction mechanisms leading up to these products. In light of this, the total electrosynthesis method is reported for producing N, N-dimethylformamide (DMF), a widespread solvent and commodity chemical, from NO3 - and CO2. This method enabled a notable production rate of 1.24 mmol h-1 gcat -1 for DMF employing a hybrid Ag/Cu catalyst. Additionally, an impressive Faradaic efficiency (FE) of 28.6% is attained for DMF through oxidative coupling of dimethylamine using Ag/Cu catalyst. Through a distinctive retrosynthetic experimental analysis, the DMF synthesis pathway is systematically deconstructed, tracing its origins from dimethylamine to methylamine, and ultimately to CO2 and NO3 -. The investigation revealed that the hydrogenation of coupled intermediates proves to be the limiting step, rather than the C-N coupling steps in the synthetic pathway. Finally, using a combination of in situ measurements and retrosynthetic analysis, the possible mechanism is elucidated underlying DMF synthesis and identified subsequent routes for system improvement.

Investigation of Electron Transfer Properties on Silicalite-1 Zeolite for Potential Electrocatalytic Applications

To develop high-performance electrocatalysts is critical to sustainable conversion and storage of renewable energy. Silicalite-1 (S-1) zeolite is considered promising for constructing electrocatalysts featuring uniform and precise porosity and a stable structural skeleton even at extreme potentials. However, its electrochemical properties remain poorly understood, particularly regarding the roles of internal pore channels. Herein, inner- and outer-sphere electron transfer (ISET/OSET) routes on the S-1 zeolite were investigated by classical redox probes. The results for the first time revealed that the ISET kinetics inside the pores of S-1 zeolite is more rapid than that on external surfaces, optimized by microporous scale channels and terminated hydroxyl groups. Conversely, the kinetics of the OSET did not closely depend on the porosity and surface properties of the S-1 zeolite. These electrochemical insights further initiated a lithium-ion-incorporated S-1 zeolite with rapid ISET kinetics for electrocatalysis of oxygen reduction. It demonstrated a high performance of 85% selectivity for H2O2 production in a neutral solution and a yield of 9.2 mol gcat-1 h-1 when configured in a flow cell.

Selective urea electrosynthesis via nitrate and CO2 reduction on uncoordinated Zn nanosheets

Electroreduction of NO3- and CO2 to urea (ENCU) represents a fascinating strategy to enable waste NO3-/CO2 removal and sustainable urea production. Herein, uncoordinated Zn nanosheets (U-Zn) are developed as a highly selective ENCU catalyst, exhibiting the highest urea-faradaic efficiency of 31.8% with the corresponding urea yield rate of 39.3 mmol h-1 g-1 in a flow cell. Theoretical calculations and electrochemical spectroscopic measurements reveal that the high ENCU performance of U-Zn arises from the critical role of uncoordinated Zn sites that can promote both key steps of *NO2/CO2 coupling and *CO2NH2 protonation to *COOHNH2, while retarding the competitive side reactions.

Atomic-Scale Tailoring C-N Coupling Sites for Efficient Acetamide Electrosynthesis over Cu-Anchored Boron Nitride Nanosheets

Electrochemical conversion of carbon and nitrogen sources into valuable chemicals provides a promising strategy for mitigating CO2 emissions and tackling pollutants. However, efficiently scaling up C-N products beyond basic compounds like urea remains a significant challenge. Herein, we upgrade the C-N coupling for acetamide synthesis through coreducing CO and nitrate (NO3-) on atomic-scale Cu dispersed on boron nitride (Cu/BN) nanosheets. The specific form of Cu, such as single atom, nanocluster, and nanoparticles, endows Cu/BN different adsorption capacity for CO and NO3-, thereby dictating the catalytic activity and selectivity for acetamide formation. The Cu nanocluster-anchored BN (Cu NCs/BN) catalyst achieves an industrial-level current density of 178 mA cm-2 for the C-N coupling reaction and an average acetamide yield rate of 137.0 mmol h-1 gcat.-1 at -1.6 V versus the reversible hydrogen electrode. Experimental and theoretical analyses uncover the pivotal role of the strong electronic interaction between Cu nanoclusters and BN, which activates CO and NO3-, facilitates the formation of key *CCO and *NH2 intermediates, and expedites the C-N coupling pathway to acetamide. This work propels the development of atomic structure catalysts for the efficient conversion of small molecules to high-value chemicals through electrochemical processes.

Electroreduction of CO2 and nitrate for urea synthesis on a low-coordinated copper catalyst

Electroreduction of CO2 and NO3- to urea (ECNU) offers a fascinating route for migrating NO3- pollutants and synthesizing valuable urea. Herein, low-coordinated copper (L-Cu) is developed as an effective ECNU catalyst, delivering the highest urea yield rate of 30.96 mmol h-1 g-1 and urea-faradaic efficiency of 50.42% in a flow cell. Theoretical calculations reveal that Cu sites and low-coordinated Cu (CuL) sites on L-Cu can synergistically promote C-N coupling and inhibit the competing side reactions, leading to a high CO2/NO3--to-urea efficiency.

Efficient urea electrosynthesis from nitrite and CO2 reduction on single W atom catalyst

Electroreduction of CO2 and NO2- to urea (ECNU) provides a fascinating method for concurrently migrating polluted NO2- and producing value-added urea. In this study, atomically dispersed W on MoS2 (W1/MoS2) is designed as an efficient ECNU catalyst, which exhibits the highest Faraday efficiency of 60.11 % and urea yield rate of 35.80 mmol h-1 g-1 in flow cell. Atomic characterizations reveal that W single atoms exist as isolated W1-S3 moieties on MoS2. Combined theoretical calculations and operando spectroscopic measurements demonstrate that the enhanced ECNU performance of W1/MoS2 arises from the construction of W1-S3 moieties that can promote CN coupling and hydrogenation energetics, whilst suppressing the competing side reactions.

Mapping Reaction Pathways by In Situ Step Sweep Voltammetry Flow Electrochemical Mass Spectrometry

A step sweep voltammetry (SSV) flow electrochemical (EC) mass spectrometry (MS) platform was developed for real-time and in situ mapping of EC reaction pathways. By integrating a flow EC cell into the pneumatic spray nozzle followed by atmospheric chemical ionization, this setup was capable of in situ MS monitoring of short-lived EC intermediates with enhanced sensitivity. This setup also realized precise measurement and control of the electrode potential during in situ EC-MS analysis, which can provide detailed information on the interplay of reaction pathways under different electrode potentials. Taking the EC reductive cross coupling of nitroarenes with arylboronic acids as an example, SSV-MS had identified 13 compounds among four reaction pathways. Among these, the electrode potential of active nitrene and cross coupling intermediates were measured for the first time and the structure of the nitroso coupling complex was also confirmed by MS. With the systematic measurement of electrode potential of the intermediates and products, SSV-MS had clearly mapped out the synergies and competitions between different reaction pathways, offering key insights for optimizing reaction conditions and investigating reaction mechanisms for EC research.

Relay Catalysis of Isolated Rhodium-Alloyed Copper Boosts Urea Electrosynthesis from Nitrate and CO2

Urea electrosynthesis from the coelectrolysis of NO3- and CO2 (UENC) presents a fascinating approach for simultaneously migrating NO3- pollutants and producing valuable urea. In this study, isolated Rh-alloyed copper (Rh1Cu) is explored as a highly active and selective catalyst toward the UENC. Combined in situ spectroscopic analysis and theoretical calculations reveal the relay catalysis of the Rh1 site and Cu site to promote the UENC energetics, in which the Rh1 site activates NO3- to form *NH2 while the Cu site activates CO2 to form *CO. The formed *CO is then migrated from the Cu substrate to the nearby Rh1 site, which promotes the C-N coupling of *NH2 and *CO toward the urea formation. Prominently, Rh1Cu achieves an exceptional UENC performance in the flow cell, exhibiting the highest urea-Faradaic efficiency of 67.10% and urea yield rate of 50.36 mmol h-1 g-1 at -0.6 V versus RHE.

Electrosynthesis of Amino Acids from Biomass and Nitrate at Industrial Current Densities Using Porous PbBi Electrodes

Electrosynthesis is a rising and attractive method for efficient amino acid production. However, industrial-grade electrosynthesis of high-value amino acids from simple carbon and nitrogen substrates is confronted with a great challenge. Herein, we design a dual-site PbBi alloy catalyst for various amino acids' electrosynthesis from keto acids and nitrate. An alanine Faradaic efficiency of 59.7% is delivered at -1.5 V vs SCE, reaching the industrial current density of 570 mA cm-2 with high catalytic durability of the porous Pb1Bi0.1 catalyst. In the tandem reaction process, nitrate is first converted to NH2OH via electrochemical reduction mainly over the Bi site. Then the obtained NH2OH integrates with the α-keto acid to form the oxime intermediate. Lastly, the Pb site facilitates the electroreduction of oxime to the final amino acids. More importantly, over 10 kinds of α-amino acids can be successfully synthesized in excellent FE and high yield at high current density, indicating the superior catalytic activity and wide universality of our strategy. In short, this work opens up a novel approach to realize the one-pot electrosynthesis of various amino acids from renewable biomass feedstocks and nitrate waste industrially.

Boosting Electroreduction of Nitrate and CO2 to Urea on a Tandem Fe1/MoS2 Catalyst

Urea electrosynthesis by coelectrolysis of NO3- and CO2 (UENC) holds enormous promise for sustainable urea production, while the efficient UENC process relies on the rational design of high-performance catalysts to facilitate the electrocatalytic C-N coupling efficiency and the hydrogenation reaction process. Herein, Fe single atoms supported on MoS2 (Fe1/MoS2) are developed as a highly effective and robust catalyst for UENC. Theoretical calculations and operando spectroscopic measurements reveal a tandem catalysis mechanism of the Fe1-S3 motif and MoS2-edge to jointly promote the UENC process, where the Fe1-S3 motif drives the early C-N coupling and subsequent *CO2NO2-to-*CO2NH2 step. The generated *CO2NH2 is then migrated from the Fe1-S3 motif to the nearby MoS2-edge, which facilitates the *CO2NH2 → *COOHNH2 step for urea formation. Noticeably, Fe1/MoS2 assembled in a flow cell reaches a maximum urea Faraday efficiency of 54.98% with a corresponding urea yield rate of 18.98 mmol h-1 g-1, performing at the top level among all of the UENC catalysts reported to date.

Recent Progress in the Electrochemical Formation of C-N Bonds for Construction of Organic Compounds via the Use of NOx/NOx. CHEMSUSCHEM 2024:e202401751. [PMID: 39375153 DOI: 10.1002/cssc.202401751] [Citation(s) in RCA: 0] [Impact Index Per Article: 0]

Emissions of nitrogen oxide (NOx) species (NO and NO2) and nitrate/nitrite NOx -, such as NO3 - and NO2 -, have led to serious water pollution and climate challenges. How to remove these wastes is a global problem that urgently needs to be addressed. As reported, electrochemical catalytic technology under ambient conditions is of great interest for NOx/NOx - removal. Additionally, the in situ utilization of surface-adsorbed nucleophilic intermediates generated from the electrochemical reduction of NOx/NOx - can provide a sustainable strategy for building C-N bonds, upgrading waste NOx/NOx - into value-added organic products, such as amines, oximes, amides, and amino acids, while remediating the environment. This review summarizes the most recent progress in the construction of nitrogen compounds by coupling electrochemical NOx/NOx - reduction reactions with inorganic/organic substrates, focuses on understanding the adsorption-transformation mechanism during the NOx/NOx - reduction process, and discusses multiple side reactions and complex pathways. Important strategies, such as coupled system development and catalyst preparation, are also presented to broaden the range of nitrogen compounds and improve yields. Finally, a few key challenges and future research directions for the development of efficient and low-cost electrochemical C-N coupling processes are discussed.

Unlocking metal-ligand cooperative catalytic photochemical benzene carbonylation: a mechanistic approach

A key challenge in green synthesis is the catalytic transformation of renewable substrates at high atom and energy efficiency, with minimal energy input (ΔG ≈ 0). Non-thermal pathways, i.e., electrochemical and photochemical, can be used to leverage renewable energy resources to drive chemical processes at well-defined energy input and efficiency. Within this context, photochemical benzene carbonylation to produce benzaldehyde is a particularly interesting, albeit challenging, process that combines unfavorable thermodynamics (ΔG° = 1.7 kcal mol-1) and the breaking of strong C-H bonds (113.5 kcal mol-1) with full atom efficiency and the use of renewable starting materials. Herein, we present a mechanistic study of photochemical benzene carbonylation catalyzed by a rhodium-based pincer complex that is capable of metal-ligand cooperation. The catalytic cycle, comprising both thermal and non-thermal steps, was probed by NMR spectroscopy, UV-visible spectroscopy and spectrophotochemistry, and density functional theory calculations. This investigation provided us with a detailed understanding of the reaction mechanism, allowing us to unlock the catalytic reactivity of the Rh-pincer complex, which represents the first example of a metal-ligand cooperative system for benzene carbonylation, exhibiting excellent selectivity.

Electrocatalytic Synthesis of Urea: An In-depth Investigation from Material Modification to Mechanism Analysis

Industrial urea synthesis production uses NH3 from the Haber-Bosch method, followed by the reaction of NH3 with CO2, which is an energy-consuming technique. More thorough evaluations of the electrocatalytic C-N coupling reaction are needed for the urea synthesis development process, catalyst design, and the underlying reaction mechanisms. However, challenges of adsorption and activation of reactant and suppression of side reactions still hinder its development, making the systematic review necessary. This review meticulously outlines the progress in electrochemical urea synthesis by utilizing different nitrogen (NO3 -, N2, NO2 -, and N2O) and carbon (CO2 and CO) sources. Additionally, it delves into advanced methods in materials design, such as doping, facet engineering, alloying, and vacancy introduction. Furthermore, the existing classes of urea synthesis catalysts are clearly defined, which include 2D nanomaterials, materials with Mott-Schottky structure, materials with artificially frustrated Lewis pairs, single-atom catalysts (SACs), and heteronuclear dual-atom catalysts (HDACs). A comprehensive analysis of the benefits, drawbacks, and latest developments in modern urea detection techniques is discussed. It is aspired that this review will serve as a valuable reference for subsequent designs of highly efficient electrocatalysts and the development of strategies to enhance the performance of electrochemical urea synthesis.

State of Play of Critical Mineral-Based Catalysts for Electrochemical E-Refinery to Synthetic Fuels

The pursuit of decarbonization involves leveraging waste CO2 for the production of valuable fuels and chemicals (e.g., ethanol, ethylene, and urea) through the electrochemical CO2 reduction reactions (CO2RR). The efficacy of this process heavily depends on electrocatalyst performance, which is generally reliant on high loading of critical minerals. However, the supply of these minerals is susceptible to shortage and disruption, prompting concerns regarding their usage, particularly in electrocatalysis, requiring swift innovations to mitigate the supply risks. The reliance on critical minerals in catalyst fabrication can be reduced by implementing design strategies that improve the available active sites, thereby increasing the mass activity. This review seeks to discuss and analyze potential strategies, challenges, and opportunities for improving catalyst activity in CO2RR with a special attention to addressing the risks associated with critical mineral scarcity. By shedding light onto these aspects of critical mineral-based catalyst systems, this review aims to inspire the development of high-performance catalysts and facilitates the practical application of CO2RR technology, whilst mitigating adverse economic, environmental, and community impacts.

Recent progress in electrochemical C-N coupling: metal catalyst strategies and applications

Electrochemical C-N coupling reactions hold significant importance in the fields of organic chemistry and green chemistry. Conventional methods for constructing C-N bonds typically rely on high temperatures, high pressures, and other conditions that are energy-intensive and prone to generating environmental pollutants. In contrast, the electrochemical approaches employ electrical energy as the driving force to achieve C-N bond formation under ambient conditions, representing a more environment-friendly and sustainable alternative. The notable advantages of electrochemical C-N coupling include high efficiency, good selectivity, and mild reaction conditions. Through rational design of corresponding electrocatalysts, it is possible to achieve efficient C-N bond coupling at low potentials. Moreover, the electrochemical methods allow for precise control over reaction conditions, thereby avoiding side reactions and by-products that are common for conventional methods, improving both selectivity and product purity. Despite the extensive research efforts devoted to exploring the potential of electrochemical C-N coupling, the design of efficient and stable metal catalysts remains a significant challenge. In this review, we summarize and evaluate the latest strategies developed for designing metal catalysts, and their application prospects for different nitrogen sources such as N2 and NOx. We delineate how the control over nanoscale structures, morphologies, and electronic properties of metal catalysts can optimize their performance in C-N coupling reactions, and discuss the performances and advantages of single-metal catalysts, bimetallic catalysts, and single-atom catalysts under various reaction conditions. By summarizing the latest research achievements, particularly in the development of high-efficiency catalysts, the application of novel catalyst materials, and the in-depth study of reaction mechanisms, this review aims to provide insights for future research in the field of electrochemical C-N coupling, and demonstrates that rationally designed metal catalysts could not only enhance the efficiency and selectivity of electrochemical C-N coupling reactions, but also offer conceptual frameworks for other electrochemical reactions.

Single-Atom Rh1 Alloyed Co for Urea Electrosynthesis from CO2 and NO3. NANO LETTERS 2024;24:10928-10935. [PMID: 39162303 DOI: 10.1021/acs.nanolett.4c02767] [Citation(s) in RCA: 0] [Impact Index Per Article: 0]

Single-atom Rh1 alloyed Co (Rh1Co) is explored as an efficient catalyst for urea electrosynthesis via coelectrolysis of CO2 and NO3- (UECN). Theoretical calculations and in situ spectroscopic measurements unravel the synergetic effect of Co and Rh1 in promoting the UECN process, where the Rh1 site activates NO3- to form *NH2, while the Co site activates CO2 to form *CO. The formed *CO then desorbs from the Co site and transfers to the Rh1 site, followed by continuous C-N coupling with *NH2 formed on the Rh1 site to synthesize urea. Remarkably, Rh1Co assembled in a flow cell delivers the exceptional urea yield rate of 24.9 mmol h-1 g-1 and Faradaic efficiency of 51.1%, outperforming most previously reported UECN catalysts.

Selective Synthesis of Organonitrogen Compounds via Electrochemical C-N Coupling on Atomically Dispersed Catalysts

The C-N coupling reaction demonstrates broad application in the fabrication of a wide range of high value-added organonitrogen molecules including fertilizers (e.g., urea), chemical feedstocks (e.g., amines, amides), and biomolecules (e.g., amino acids). The electrocatalytic C-N coupling pathways from waste resources like CO2, NO3-, or NO2- under mild conditions offer sustainable alternatives to the energy-intensive thermochemical processes. However, the complex multistep reaction routes and competing side reactions lead to significant challenges regarding low yield and poor selectivity toward large-scale practical production of target molecules. Among diverse catalyst systems that have been developed for electrochemical C-N coupling reactions, the atomically dispersed catalysts with well-defined active sites provide an ideal model platform for fundamental mechanism elucidation. More importantly, the intersite synergy between the active sites permits the enhanced reaction efficiency and selectivity toward target products. In this Review, we systematically assess the dominant reaction pathways of electrocatalytic C-N coupling reactions toward various products including urea, amines, amides, amino acids, and oximes. To guide the rational design of atomically dispersed catalysts, we identify four key stages in the overall reaction process and critically discuss the corresponding catalyst design principles, namely, retaining NOx/COx reactants on the catalyst surface, regulating the evolution pathway of N-/C- intermediates, promoting C-N coupling, and facilitating final hydrogenation steps. In addition, the advanced and effective theoretical simulation and characterization technologies are discussed. Finally, a series of remaining challenges and valuable future prospects are presented to advance rational catalyst design toward selective electrocatalytic synthesis of organonitrogen molecules.

Progress and challenges in nitrous oxide decomposition and valorization

Nitrous oxide (N2O) decomposition is increasingly acknowledged as a viable strategy for mitigating greenhouse gas emissions and addressing ozone depletion, aligning significantly with the UN's sustainable development goals (SDGs) and carbon neutrality objectives. To enhance efficiency in treatment and explore potential valorization, recent developments have introduced novel N2O reduction catalysts and pathways. Despite these advancements, a comprehensive and comparative review is absent. In this review, we undertake a thorough evaluation of N2O treatment technologies from a holistic perspective. First, we summarize and update the recent progress in thermal decomposition, direct catalytic decomposition (deN2O), and selective catalytic reduction of N2O. The scope extends to the catalytic activity of emerging catalysts, including nanostructured materials and single-atom catalysts. Furthermore, we present a detailed account of the mechanisms and applications of room-temperature techniques characterized by low energy consumption and sustainable merits, including photocatalytic and electrocatalytic N2O reduction. This article also underscores the extensive and effective utilization of N2O resources in chemical synthesis scenarios, providing potential avenues for future resource reuse. This review provides an accessible theoretical foundation and a panoramic vision for practical N2O emission controls.

Sustainable Electrosynthesis of N,N-Dimethylformamide via Relay Catalysis on Synergistic Active Sites

Electrified synthesis of high-value organonitrogen chemicals from low-cost carbon- and nitrogen-based feedstocks offers an economically and environmentally appealing alternative to traditional thermocatalytic methods. However, the intricate electrochemical reactions at electrode surfaces pose significant challenges in controlling selectivity and activity, especially for producing complex substances such as N,N-dimethylformamide (DMF). Herein, we tackle this challenge by developing relay catalysis for efficient DMF production using a composite WO2-NiOOH/Ni catalyst with two distinctive active sites. Specifically, WO2 selectively promotes dimethylamine (DMA) electrooxidation to produce strongly surface-bound (CH3)2N*, while nearby NiOOH facilitates methanol electrooxidation to yield more weakly bound *CHO. The disparity in binding energetics of the key C- and N-intermediates expedites C-N coupling at the WO2-NiOOH interface. In situ infrared spectroscopy with isotope-labeling experiments, quasi-in situ electron paramagnetic resonance trapping experiments, and electrochemical operating experiments revealed the C-N coupling mechanism and enhanced DMF-synthesis selectivity and activity. In situ X-ray absorption spectroscopy (XAS) and postreaction transmission electron microscopy (TEM) studies verified the stability of WO2-NiOOH/Ni during extended electrochemical operation. A Faradaic efficiency of ∼50% and a production rate of 438 μmol cm-2 h-1 were achieved at an industrially relevant current density of 100 mA cm-2 over an 80 h DMF production period. This study introduces a new paradigm for developing electrothermo relay catalysis for the sustainable and efficient synthesis of valuable organic chemicals with industrial potential.

Electrocatalytic Coupling of Nitrate and Formaldehyde for Hexamethylenetetramine Synthesis via C-N Bond Construction and Ring Formation

Hexamethylenetetramine (HMTA) is extensively used in the defense industry, medicines, food, plastics, rubber, and other applications. Traditional organic synthesis of HMTA relies on ammonia derived from the Haber process at high temperatures and pressures. In contrast, electrochemical methods enable a safe and green one-pot synthesis of HMTA from waste NO3-. However, HMTA synthesis through the electrochemical method is challenging owing to the complex reaction pathways involving C-N bond construction and ring formation. In this study, HMTA was efficiently synthesized over electrochemical oxidation-derived copper (e-OD-Cu), with a yield of 76.8% and a Faradaic efficiency of 74.9% at -0.30 VRHE. The catalytic mechanism and reaction pathway of HMTA synthesis on e-OD-Cu were investigated through a series of in situ characterization methods and density-functional theory calculations. The results demonstrated that the electrocatalytic synthesis of HMTA involved a tandem electrochemical-chemical reaction. Additionally, the results indicated that the presence of Cu vacancies enhanced substrate adsorption and inhibited the further hydrogenation of C═N. Overall, this study provides an electrocatalytic method for HMTA synthesis and an electrochemical strategy for constructing multiple C-N bonds.

Boosting Electrochemical Urea Synthesis via Constructing Ordered Pd-Zn Active Pair

Electrochemical co-reduction of nitrate (NO3-) and carbon dioxide (CO2) has been widely regarded as a promising route to produce urea under ambient conditions, however the yield rate of urea has remained limited. Here, we report an atomically ordered intermetallic pallium-zinc (PdZn) electrocatalyst comprising a high density of PdZn pairs for boosting urea electrosynthesis. It is found that Pd and Zn are responsible for the adsorption and activation of NO3- and CO2, respectively, and thus the co-adsorption and co-activation NO3- and CO2 are achieved in ordered PdZn pairs. More importantly, the ordered and well-defined PdZn pairs provide a dual-site geometric structure conducive to the key C-N coupling with a low kinetical barrier, as demonstrated on both operando measurements and theoretical calculations. Consequently, the PdZn electrocatalyst displays excellent performance for the co-reduction to generate urea with a maximum urea Faradaic efficiency of 62.78% and a urea yield rate of 1274.42 μg mg-1 h-1, and the latter is 1.5-fold larger than disordered pairs in PdZn alloys. This work paves new pathways to boost urea electrosynthesis via constructing ordered dual-metal pairs.

Urea Electrosynthesis from Nitrate and CO2 on Diatomic Alloys

Urea electrosynthesis from co-electrolysis of NO3 - and CO2 (UENC) offers a promising technology for achieving sustainable and efficient urea production. Herein, a diatomic alloy catalyst (CuPd1Rh1-DAA), with mutually isolated Pd and Rh atoms alloyed on Cu substrate, is theoretically designed and experimentally confirmed to be a highly active and selective UENC catalyst. Combining theoretical computations and operando spectroscopic characterizations reveals the synergistic effect of Pd1-Cu and Rh1-Cu active sites to promote the UENC via a tandem catalysis mechanism, where Pd1-Cu site triggers the early C-N coupling and promotes *CO2NO2-to-*CO2NH steps, while Rh1-Cu site facilitates the subsequent protonation step of *CO2NH2 to *COOHNH2 toward the urea formation. Impressively, CuPd1Rh1-DAA assembled in a flow cell presents the highest urea Faradaic efficiency of 72.1% and urea yield rate of 53.2 mmol h-1 gcat -1 at -0.5 V versus RHE, representing nearly the highest performance among all reported UENC catalysts.

Cu-Mo Dual Sites in Cu-Doped MoSe2 for Enhanced Electrosynthesis of Urea

The quest for sustainable urea production has directed attention toward electrocatalytic methods that bypass the energy-intensive traditional Haber-Bosch process. This study introduces an approach to urea synthesis through the coreduction of CO2 and NO3- using copper-doped molybdenum diselenide (Cu-MoSe2) with Cu-Mo dual sites as electrocatalysts. The electrocatalytic activity of the Cu-MoSe2 electrode is characterized by a urea yield rate of 1235 μg h-1 mgcat.-1 at -0.7 V versus the reversible hydrogen electrode and a maximum Faradaic efficiency of 23.43% at -0.6 V versus RHE. Besides, a continuous urea production with an enhanced average yield rate of 9145 μg h-1 mgcat.-1 can be achieved in a flow cell. These figures represent a substantial advancement over that of the baseline MoSe2 electrode. Density functional theory (DFT) calculations elucidate that Cu doping accelerates *NO2 deoxygenation and significantly decreases the energy barriers for C-N bond formation. Consequently, Cu-MoSe2 demonstrates a more favorable pathway for urea production, enhancing both the efficiency and feasibility of the process. This study offers valuable insights into electrode design and understanding of the facilitated electrochemical pathways.

Catalysts for C-N coupling in urea electrosynthesis under ambient conditions from carbon dioxide and nitrogenous species

Urea is an indispensable nitrogen-containing organic compound in modern human life. However, the current industrial synthesis of urea involves ammonia, which is produced through the Haber-Bosch process under harsh reaction conditions, causing huge energy consumption and heavy environmental pollution. Electrochemical reduction of carbon dioxide (CO2) and nitrogenous species (N2, NOx- and NO) have achieved significant progress, offering a promising approach for the electrochemical C-N coupling to produce urea under ambient conditions. Urea synthesis driven by renewable electricity represents a suitable alternative to the traditional process, contributing to the goal of carbon neutrality and nitrogen cycles. However, challenges such as low yield rate, poor selectivity and unveiled reaction mechanisms still need to be addressed. This review provides a summary of the latest catalysts utilized in urea electrosynthesis, aiming to provide guidance and prospects for the development of high-performance catalysts.