Electrocatalytic Urea Research Articles

Modification of nickel foam with nickel phosphate catalyst layer via anodizing for boosting the electrocatalytic urea oxidation and hydrogen evolution reactions

Urea oxidation reaction (UOR) and hydrogen evolution reaction (HER) are the key processes for implementing urinated water electrolysis and hydrogen green production, respectively. This contribution investigates the modification of commercial nickel foam (NF) with a nickel phosphate (NiPO/NF) heterostructure layer via anodizing in phosphate solution at various potentials (5, 10 and 15 V) as a simple and efficient route to boost the urea-assisted water electrolysis and hydrogen production in alkaline medium. The morphology and composition physicochemical characterisation of the phosphate layer exhibit aggregates of crystalline nanoparticles with interstitial mesoporous and macroporous networks with a mole composition ratio of 9.42: 1.0: 8.14 for Ni: P: O respectively. The electrochemical measurements revealed the NiPO/NF anodized at 10 V exhibits a superior electroactive surface area of 255 cm2, a substantially higher urea oxidation current compared to pristine NF, achieving 20 and 500 mA/cm2 at 1.35 and 1.6 V vs. RHE respectively and retained 100 % of activity during the urea electrolysis for more than 3 h. The electrochemical impedance analysis confirmed the alkaline urea oxidation reaction proceeded via indirect (EC) and direct mechanism and the CO2 intermediates adsorption–desorption became the predominant reaction at more positive potential. The NiPO/NF anode employed in an H-shape can deliver up to ±400 mA/cm2 for UOR/HER at a bias potential of 1.85 V and 8-fold (2.0 mmol/min) much higher hydrogen production rate compared to the pristine NF anode (0.25 mmol/min). Combining commercial nickel foam modification via anodizing and alkaline urea electrolysis at ambient conditions offers a unique and innovative solution for both large-scale hydrogen green production as well as remedy of the urinated wastewater for a more sustainable future.

Nano FeNi-OH/Co(OH)2/NF p-n heterojunction for efficient oxygen evolution reaction and electrocatalytic urea oxidation: Built-In electric field regulated charge distribution and mechanism exploration

Constructing electronic structures with abundant surface/interface structures and effective regulation of catalytic active centers is an effective strategy to improve electrocatalytic performance, but designing efficient bifunctional non-noble metal oxygen evolution reaction (OER) and urea oxidation reaction (UOR) electrocatalysts remains challenging. Studies have shown that p-n heterojunctions can effectively regulate the electronic structure of catalytic active sites while having abundant surface/interface structure, which plays an important role in improving the native catalytic activity. Herein, FeNi-OH/Co(OH)2/NF p-n heterojunction structure was constructed by a simple electrochemical deposition method, and the effects of content, deposition time, and number of cycles on catalytic performance were investigated. The results show that Fe(0.02 M)Ni(0.07 M)–OH(100 s)/Co(OH)2(5)/NF composite material has the best OER and UOR catalytic performance. For OER, the electrocatalyst only requires an overpotential of 271 mV to obtain a current density of 50 mA cm−2, and an applied voltage of 1.56 V to obtain a total water decomposition of 10 mA cm−2 (FeNi-OH/Co(OH)2/NF||Pt). For UOR, a voltage of only 1.314 V (vs. RHE) is required to achieve a current density of 10 mA cm−2, and an applied voltage of 1.44 V can achieve a current density of 10 mA cm−2. Experimental, in situ measurements and theoretical results indicate that the improvement in catalytic activity is mainly due to the potential difference between FeNi-OH and Co(OH)2, which induces self-driven charge transfer at the interface, promoting the adsorption of reactant molecules, optimizing reaction barriers, accelerating chemical bond cleavage, and thus promoting catalytic reactions.

Efficient Electrocatalytic Urea Formation from Gas Pollutants on Heteronuclear Dual-Metal Atom Anchored N-Doped Graphene

Efficient Electrocatalytic Urea Formation from Gas Pollutants on Heteronuclear Dual-Metal Atom Anchored N-Doped Graphene

Ru nanocrystals modified porous FeOOH nanostructures with open 3D interconnected architecture supported on NiFe foam as high‐performance electrocatalyst for oxygen evolution reaction and electrocatalytic urea oxidation

The construction of binder-free electrodes with well-defined three-dimensional (3D) morphology and optimized electronic structure represents an efficient strategy for the design of high-performance electrocatalysts for the development of efficient green hydrogen technologies. Herein, Ru nanocrystals were modified on 3D interconnected porous FeOOH nanostructures with open network-like frameworks on NiFe foam (Ru/FeOOH@NFF), which were used as an efficient electrocatalyst. In this study, a 3D interconnected porous FeOOH with an open network structure was first electrodeposited on NiFe foam and served as the support for the in-situ modification of Ru nanocrystals. Subsequently, the Ru nanocrystals and abundant oxygen vacancies were simultaneously incorporated into the FeOOH matrix via the adsorption-reduction method, which involved NaBH4 reduction. The Ru/FeOOH@NFF electrocatalyst shows a large specific surface area, abundant oxygen vacancies, and modulated electronic structure, which collectively result in a significant enhancement of catalytic properties with respect to the oxygen evolution reaction (OER) and urea oxidation reaction (UOR). The Ru/FeOOH@NFF catalyst exhibits an outstanding OER performance, requiring a low overpotential (360 mV) at 200 mA cm−2 with a small Tafel slope (58 mV dec-1). Meanwhile, the Ru/FeOOH@NFF catalyst demonstrates more efficient UOR activity for achieving 200 mA cm−2 at a lower overpotential of 272 mV. Furthermore, an overall urea electrolysis cell using the Ru/FeOOH@NFF as the anode and Pt as the cathode (Ru/FeOOH@NFF||Pt) reveals a cell voltage of 1.478 V at 10 mA cm−2 and a prominent durability (120 h at 50 mA cm−2). This work will provide a valuable understanding of the construction of high-performance electrocatalysts with 3D microstructure for promoting urea-assisted water electrolysis.

Structural Design of Nickel Hydroxide for Efficient Urea Electrooxidation.

Urea stands as a ubiquitous environmental contaminant. However, not only does urea oxidation reaction technology facilitate energy conversion, but it also significantly contributes to treating wastewater rich in urea. Furthermore, urea electrolysis has a significantly lower theoretical potential (0.37 V) compared to water electrolysis (1.23 V). As an electrochemical reaction, the catalytic efficacy of urea oxidation is largely contingent upon the catalyst employed. Among the plethora of urea oxidation electrocatalysts, nickel-based compounds emerge as the preeminent transition metal due to their cost-effectiveness and heightened activity in urea oxidation. Ni(OH)2 is endowed with manifold advantages, including structural versatility, facile synthesis, and stability in alkaline environments. This review delineates the recent advancements in Ni(OH)2 catalysts for electrocatalytic urea oxidation reaction, encapsulating pivotal research findings in morphology, dopant incorporation, defect engineering, and heterogeneous architectures. Additionally, we have proposed personal insights into the challenges encountered in the research on nickel hydroxide for urea oxidation, aiming to promote efficient urea conversion and facilitate its practical applications.

Mesoporous Electrocatalysts with p-n Heterojunctions for Efficient Electroreduction of CO2 and N2 to Urea.

The electrocatalytic synthesis of high-value-added urea by activating N2 and CO2 is a green synthesis technology that has achieved carbon neutrality. However, the chemical adsorption and C-N coupling ability of N2 and CO2 on the surface of the catalyst are generally poor, greatly limiting the improvement of electrocatalytic activity and selectivity in electrocatalytic urea synthesis. Herein, novel hierarchical mesoporous CeO2/Co3O4 heterostructures are fabricated, and at an ultralow applied voltage of -0.2 V, the urea yield rate reaches 5.81 mmol g-1 h-1, with a corresponding Faraday efficiency of 30.05%. The hierarchical mesoporous material effectively reduces the mass transfer resistance of reactants and intermediates, making it easier for them to access active centers. The emerging space-charge regions at the heterointerface generate local electrophilic and nucleophilic regions, facilitating CO2 targeted adsorption in the electrophilic region and activation to produce *CO intermediates and N2 targeted adsorption in the nucleophilic region and activation to generate *N ═ N* intermediates. Then, the electrons in the σ orbitals of *N ═ N* intermediates can be easily accepted by the empty eg orbitals of Co3+ in CeO2/Co3O4, which presents a low-spin state (LS: t2g6eg0). Subsequently, *CO couples with *N ═ N* to produce the key intermediate *NCON*. Interestingly, it was discovered through in situ Raman spectroscopy that the CeO2/Co3O4 catalyst has a reversible spinel structure before and after the electrocatalytic reaction, which is due to the surface reconstruction of the catalyst during the electrocatalytic reaction process, producing amorphous active cobalt oxides, which is beneficial for improving electrocatalytic activity.

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

Electrocatalytic urea synthesis from CO2 and nitrogenous substances represents an essential advance for the chemical industry, enabling the efficient utilization of resources and promoting sustainable development. However, the development of electrocatalytic urea synthesis has been severely limited by weak chemisorption, poor activation and difficulties in C-N coupling reactions. In this review, catalysts and corresponding reaction mechanisms in the emerging fields of bimetallic catalysts, MXenes, frustrated Lewis acid-base pairs and heterostructures are summarized in terms of the two central mechanisms of molecule-catalyst interactions as well as chemical bond cleavage and directional coupling, which provide new perspectives for improving the efficiency of electrocatalytic synthesis of urea. This review provides valuable insights to elucidate potential electrocatalytic mechanisms.

Overcoming Electrostatic Interaction via Pulsed Electroreduction for Boosting the Electrocatalytic Urea Synthesis

AbstractElectrocatalytic urea synthesis under ambient conditions offers a promising alternative strategy to the traditional energy‐intensive urea industry protocol. Limited by the electrostatic interaction, the reduction reaction of anions at the cathode in the electrocatalytic system is not easily achievable. Here, we propose a novel strategy to overcome electrostatic interaction via pulsed electroreduction. We found that the reconstruction‐resistant CuSiOx nanotube, with abundant atomic Cu−O−Si interfacial sites, exhibits ultrastability in the electrosynthesis of urea from nitrate and CO2. Under a pulsed potential approach with optimal operating conditions, the Cu−O−Si interfaces achieve a superior urea production rate (1606.1 μg h−1 mgcat.−1) with high selectivity (79.01 %) and stability (the Faradaic efficiency is retained at 80 % even after 80 h of testing), outperforming most reported electrocatalytic synthesis urea catalysts. We believe our strategy will incite further investigation into pulsed electroreduction increasing substrate transport, which may guide the design of ambient urea electrosynthesis and other energy conversion systems.

Coupling interface constructions of flower-like structure MoSe2–NiWSe2 for efficient oxygen evolution reaction and urea oxidation reaction

Because of its low thermodynamic voltage, the electrocatalytic urea oxidation reaction (UOR) is an effective way to replace the sluggish oxygen evolution reaction (OER) and address the issue of urea-rich water pollution. Herein, we have synthesized MoSe2–NiWSe2 with spherical nanoflower structure consisting of MoSe2 nanosheets and NiWSe2 nanosheets crisscrossed longitudinally and transversely. The results show that the prepared MoSe2–NiWSe2 has a significant competitive advantage in the UOR and OER. With 10 mA cm−2, a mere 200 mV overpotential was required, indicating high OER catalytic activity. MoSe2–NiWSe2-driven UOR might operate at a comparatively low potential of 1.36 V (10 mA cm−2). The overpotential did not significantly alter after 40 h of continuous operation, suggesting it possesses high UOR stability. A built-in electric field that aids in controlling the adsorption and oriented distribution of urea molecules and thus promotes the oxidative properties of water and urea forms at the interface of MoSe2 and NiWSe2, where the difference in electronegativity between the elements Mo and Ni induces self-driven charge transfer and interfacial coupling effects. This work offers a method for creating catalysts that produce more oxygen and clean up urea-rich water contamination.

Overcoming Electrostatic Interaction via Pulsed Electroreduction for Boosting the Electrocatalytic Urea Synthesis.

Electrocatalytic urea synthesis under ambient conditions offers a promising alternative strategy to the traditional energy-intensive urea industry protocol. Limited by the electrostatic interaction, the reduction reaction of anions at the cathode in the electrocatalytic system is not easily achievable. Here, we propose a novel strategy to overcome electrostatic interaction via pulsed electroreduction. We found that the reconstruction-resistant CuSiOx nanotube, with abundant atomic Cu-O-Si interfacial sites, exhibits ultrastability in the electrosynthesis of urea from nitrate and CO2. Under a pulsed potential approach with optimal operating conditions, the Cu-O-Si interfaces achieve a superior urea production rate (1606.1 μg h-1 mgcat. -1) with high selectivity (79.01 %) and stability (the Faradaic efficiency is retained at 80 % even after 80 h of testing), outperforming most reported electrocatalytic synthesis urea catalysts. We believe our strategy will incite further investigation into pulsed electroreduction increasing substrate transport, which may guide the design of ambient urea electrosynthesis and other energy conversion systems.

Tandem Catalysts Enabling Efficient C-N Coupling toward the Electrosynthesis of Urea.

The development of a methodology for synthesizing value-added urea (CO(NH2)2) via a renewable electricity-driven C-N coupling reaction under mild conditions is highly anticipated. However, the complex catalytic active sites that act on the carbon and nitrogen species make the reaction mechanism unclear, resulting in a low efficiency of C-N coupling from the co-reduction of carbon dioxide (CO2) and nitrate (NO3 -). Herein, we propose a novel tandem catalyst of Mo-PCN-222(Co), in which the Mo sites serve to facilitate nitrate reduction to the *NH2 intermediate, while the Co sites enhance CO2 reduction to carbonic oxide (CO), thus synergistically promoting C-N coupling. The synthesized Mo-PCN-222(Co) catalyst exhibited a noteworthy urea yield rate of 844.11 mg h-1 g-1, alongside a corresponding Faradaic efficiency of 33.90 % at -0.4 V vs. reversible hydrogen electrode (RHE). By combining in situ spectroscopic techniques with density functional theory calculations, we demonstrate that efficient C-N coupling is attributed to a tandem system in which the *NH2 and *CO intermediates produced by the Mo and Co active sites of Mo-PCN-222(Co) stabilize the formation of the *CONH2 intermediate. This study provides an effective avenue for the design and synthesis of tandem catalysts for electrocatalytic urea synthesis.

Tandem Catalysts Enabling Efficient C−N Coupling toward the Electrosynthesis of Urea

AbstractThe development of a methodology for synthesizing value‐added urea (CO(NH2)2) via a renewable electricity‐driven C−N coupling reaction under mild conditions is highly anticipated. However, the complex catalytic active sites that act on the carbon and nitrogen species make the reaction mechanism unclear, resulting in a low efficiency of C−N coupling from the co‐reduction of carbon dioxide (CO2) and nitrate (NO3−). Herein, we propose a novel tandem catalyst of Mo‐PCN‐222(Co), in which the Mo sites serve to facilitate nitrate reduction to the *NH2 intermediate, while the Co sites enhance CO2 reduction to carbonic oxide (CO), thus synergistically promoting C−N coupling. The synthesized Mo‐PCN‐222(Co) catalyst exhibited a noteworthy urea yield rate of 844.11 mg h−1 g−1, alongside a corresponding Faradaic efficiency of 33.90 % at −0.4 V vs. reversible hydrogen electrode (RHE). By combining in situ spectroscopic techniques with density functional theory calculations, we demonstrate that efficient C−N coupling is attributed to a tandem system in which the *NH2 and *CO intermediates produced by the Mo and Co active sites of Mo‐PCN‐222(Co) stabilize the formation of the *CONH2 intermediate. This study provides an effective avenue for the design and synthesis of tandem catalysts for electrocatalytic urea synthesis.

Theoretical study of electrocatalytic urea synthesis through CO2 and N2 on metal cluster decorated C2N

Theoretical study of electrocatalytic urea synthesis through CO2 and N2 on metal cluster decorated C2N

Suppression of Passivation on Nickel Hydroxide in Electrocatalytic Urea Oxidization (Adv. Funct. Mater. 14/2024)

Suppression of Passivation on Nickel Hydroxide in Electrocatalytic Urea Oxidization (Adv. Funct. Mater. 14/2024)

Artificial Heterointerfaces with Regulated Charge Distribution of Ni Active Sites for Urea Oxidation Reaction.

In contrast to the thermodynamically unfavorable anodic oxygen evolution reaction, the electrocatalytic urea oxidation reaction (UOR) presents a more favorable thermodynamic potential. However, the practical application of UOR has been hindered by sluggish kinetics. In this study, hierarchical porous nanosheet arrays featuring abundant Ni-WO3 heterointerfaces on nickel foam (Ni-WO3/NF) is introduced as a monolith electrode, demonstrating exceptional activity and stability toward UOR. The Ni-WO3/NF catalyst exhibits unprecedentedly rapid UOR kinetics (200mAcm-2 at 1.384V vs. RHE) and a high turnover frequency (0.456s-1), surpassing most previously reported Ni-based catalysts, with negligible activity decay observed during a durability test lasting 150 h. Ex situ X-ray photoelectron spectroscopy and density functional theory calculations elucidate that the WO3 interface significantly modulates the local charge distribution of Ni species, facilitating the generation of Ni3+ with optimal affinity for interacting with urea molecules and CO2 intermediates at heterointerfaces during UOR. This mechanism accelerates the interfacial electrocatalytic kinetics. Additionally, in situ Fourier transform infrared spectroscopy provides deep insights into the substantial contribution of interfacial Ni-WO3 sites to UOR electrocatalysis, unraveling the underlying molecular-level mechanisms. Finally, the study explores the application of a direct urea fuel cell to inspire future practical implementations.

Engineering active sites on binary metal selenide heterointerface catalyst to boost urea electrooxidation

Electrocatalytic urea oxidation reaction (UOR) with a low thermodynamic potential is a perfect substitute for anodic oxygen evolution process (OER) in the effective generation of hydrogen. However, because of the slow kinetics of UOR, its potential application for commercial use remains untapped. Nickel-based materials may be an option for urea oxidation reaction but the heavily filled d orbital prevents enhanced adsorption and activity. Here, taking into account the adsorption-energy scaling limitations, Co3+ with partially filled d orbital is introduced into nickel selenide to form a heterointerface catalyst (2D CoSe2/Ni0.85Se) that enhances UOR. As anticipated, the 2D CoSe2/Ni0.85Se electrode displays a low potential of 1.33 V to achieve 100 mA cm−2 for UOR while retaining strong durability for 300 h. Further, 2D CoSe2/Ni0.85Se catalyst is used as an anode in an anion exchange membrane flow electrolyzer, which achieved an industrial-level voltage of 1.91 V at 1 A cm−2 and robust durability.

Electrocatalytic urea synthesis from CO2 and nitrate co-reduction on natural vitamin B12 coupled carbon nanotubes

The synthesis of urea from CO2 and nitrate co-electrolysis is highly attractive for the sustainable production of nitrogen-containing fertilizers such as urea. However, this process requires electrocatalysts that are not only highly active but also selective. In this study, we present a remarkable approach wherein Vitamin B12 is immobilized on the surface of carbon nanotubes to catalyze the co-electroreduction to urea under ambient conditions. This unique hybrid system, incorporating a naturally abundant molecular catalyst, exhibits exceptional selectivity and maintains a constant current density in CO2-saturated 0.1 M KNO3. Remarkably, we achieved a Faradaic efficiency (FE) of 26.04% at −0.5 V versus the reversible hydrogen electrode (RHE), resulting in a production yield of 164.04 μg h−1 mg−1 and an impressive turnover number (TON) reaching up to 830.53 while demonstrating excellent stability and durability over a period of 50 hours. Our experimental findings are further supported by density functional theory (DFT) studies that shed light on the influence exerted by the covalently attached and redox-active benzimidazole unit within Vitamin B12 molecule itself when immobilized onto conductive surfaces like carbon nanotubes. This work represents an unprecedented example where naturally abundant vitamin has been successfully immobilized on a conductive surface for achieving highly efficient electroproduction of urea.

Electrocatalytic synthesis of C–N coupling compounds from CO2 and nitrogenous species

AbstractThe electrocatalytic synthesis of C–N coupling compounds from CO2 and nitrogenous species not only offers an effective avenue to achieve carbon neutrality and reduce environmental pollution, but also establishes a route to synthesize valuable chemicals, such as urea, amide, and amine. This innovative approach expands the application range and product categories beyond simple carbonaceous species in electrocatalytic CO2 reduction, which is becoming a rapidly advancing field. This review summarizes the research progress in electrocatalytic urea synthesis, using N2, NO2−, and NO3− as nitrogenous species, and explores emerging trends in the electrosynthesis of amide and amine from CO2 and nitrogen species. Additionally, the future opportunities in this field are highlighted, including electrosynthesis of amino acids and other compounds containing C–N bonds, anodic C–N coupling reactions beyond water oxidation, and the catalytic mechanism of corresponding reactions. This critical review also captures the insights aimed at accelerating the development of electrochemical C–N coupling reactions, confirming the superiority of this electrochemical method over the traditional techniques.

Water-Stable Pillared Three-Dimensional Zn-V Bimetal-Organic Framework for Promoted Electrocatalytic Urea Oxidation.

Urea oxidation reaction (UOR) is one of the potential routes in which urea-rich wastewater is used as a source of energy for hydrogen production. Metal-organic frameworks (MOFs) have promising applications in electrocatalytic processes, although there are still challenges in identifying the MOFs' molecular regulation and obtaining practical catalytic systems. The current study sought to synthesize [Zn6(IDC)4(OH)2(Hprz)2]n (Zn-MOF) with three symmetrically independent Zn(II) cations connected via linear N-donor piperazine (Hprz), rigid planar imidazole-4,5-dicarboxylate (IDC3-), and -OH ligands, revealing the 3,4T1 topology. The optimized noble-metal-free Zn0.33V0.66-MOF/NF electrocatalysts show higher robustness and performance compared to those of the parent Zn monometallic MOF/NF electrode and other bimetallic MOFs with different Zn-V molar ratios. The low potential of 1.42 V (vs RHE) at 50 mA cm-2 in 1.0 M KOH with 0.33 M urea required by the developed Zn0.33V0.66-MOF electrode makes its application in the UOR more feasible. The availability of more exposed active sites, ion diffusion path, and higher conductivity result from the distinctive configuration of the synthesized electrocatalyst, which is highly stable and capable of synergistic effects, consequently enhancing the desired reaction. The current research contributes to introducing a practical, cost-effective, and sustainable solution to decompose urea-rich wastewater and produce hydrogen.

Dynamic Reconstruction of Two-Dimensional Defective Bi Nanosheets for Efficient Electrocatalytic Urea Synthesis.

Catalyst surface dynamics drive the generation of active species for electrocatalytic reactions. Yet, the understanding of dominant site formation and reaction mechanisms is limited. In this study, we thoroughly investigate the dynamic reconstruction of two-dimensional defective Bi nanosheets from exfoliated Bi2Se3 nanosheets under electrochemical CO2 and nitrate (NO3 -) reduction conditions. The ultrathin Bi2Se3 nanosheets obtained by NaBH4-assisted cryo-mediated liquid-phase exfoliation are more easily reduced and reconstructed to Bi nanosheets with high-density grain boundaries (GBs; GB-rich Bi). The reconstructed GB-rich Bi catalyst affords a remarkable yield rate of 4.6 mmol h-1 mgcat. -1 and Faradaic efficiency of 32 % for urea production at -0.40 V vs. RHE. Notably, this yield rate is 2 and 8.2 times higher than those of the low-GB Bi and bulk Bi catalysts, respectively. Theoretical analysis demonstrates that the GB sites significantly reduce the *CO and *NH2 intermediate formation energy and C-N coupling energy barrier, enabling selective urea electrosynthesis on the GB-rich Bi catalyst. This work will trigger further research into the structure-activity interplay in dynamic processes using in situ techniques.