Electrocatalytic Oxidation Of Urea Research Articles

Ultrathin two-dimensional nickel-organic framework nanosheets for efficient electrocatalytic urea oxidation

Synthesis of highly-efficiency electrocatalysts with controllable morphology, enriched active sites, and low cost is of great significance for urea oxidation reaction (UOR) applications. In this work, novel two-dimensional (2D) nickel-based metal-organic framework (Ni-MOF) nanosheets comprising Ni2+ and an organic ligand of 4-Dimethylaminopyridine (Ni-DMAP-t, where t is the synthesis time) are firstly synthesized by a facile one-pot solvothermal method. By thickness regulation of Ni-DMAP-t nanosheets, the self-supported Ni-DMAP-2 with the smallest thickness on Ni foam (Ni-DMAP-2/NF) exhibits high electrocatalytic activity toward UOR with a low potential of 1.45 V at a current density of 100 mA cm−2. Moreover, by further coupling with the cathodic hydrogen evolution reaction, the urea-assisted electrolytic hydrogen production system using Ni-DMAP-2/NF as anode displays a dramatic voltage reduction by 290 mV at a current density of 50 mA cm−2 as compared with that of conventional water electrolysis using the same electrodes. Such a superior UOR electrocatalytic activity of Ni-DMAP-2/NF is ascribed to the abundant Ni active sites exposed on the surface of Ni-DMAP-2, as well as the accelerated electron/ion transfer properties endowed by its ultrathin 2D nanosheets structure. This work offers some new ideas into the design and development of ultrathin 2D Ni-based MOF electrocatalysts for urea-related energy storage devices.

Optimizing local charge distribution of metal nodes in bimetallic metal–organic frameworks for efficient urea oxidation reaction

A significantly lower voltage was required in NiFe-MIL-53-NH 2 when using full urea electrolysis instead of overall water splitting. • Incorporating Fe induces the formation of electrophilic Ni 3+ and nucleophilic Fe 3+ . • The bimetallic NiFe-MIL-53-NH 2 presents excellent electrocatalytic UOR activity. • This work provides a new strategy to explore effective UOR electrocatalysts. Electrocatalytic urea oxidation reaction (UOR) presents lower thermodynamic potential than oxygen evolution reaction (OER), thus exhibiting promising potential to enhance the efficiency of overall water splitting. However, due to the intrinsically sluggish six-electron transfer process, the efficiency of UOR is still not satisfied. In response, we synthesized a bimetallic NiFe-MIL-53-NH 2 with superior activity toward UOR, which only needs a low potential of 1.398 V vs. RHE to obtain 50 mA cm −2 in 1.0 M KOH with 0.33 M urea, much lower than that in 1.0 M KOH (1.721 V vs. RHE). Furthermore, NiFe-MIL-53-NH 2 presents significantly more excellent UOR activity compared to its monometallic counterparts. The TOF value in NiFe-MIL-53-NH 2 (0.16 s −1 ) at 1.4 V vs. RHE is about 133- and 246-folds higher than that Ni-MIL-53-NH 2 (1.2 × 10 -3 s −1 ) and Fe-MIL-53-NH 2 (6.5 × 10 -4 s −1 ), respectively. XPS characterization discloses that the incorporation of Fe into Ni-MIL-53-NH 2 framework optimizes the local charge distribution of metal nodes, leading to the formation of electrophilic Ni 3+ and nucleophilic Fe 3+ species, which can absorb electron-donating –NH 2 and electron-withdrawing C = O groups in urea, respectively, and therefore result in excellent UOR. This simple strategy of regulating local charge distribution of active species by fabricating bimetallic MOFs provides a new strategy and direction to explore other highly efficient UOR electrocatalysts.

Dynamic active sites on plasma engraved Ni hydroxide for enhanced electro-catalytic urea oxidation

The urea oxidization reaction (UOR) is an important anodic reaction in electro-catalytic energy conversion. However, the sluggish reaction kinetics and complex catalyst transformation in electrocatalysis require activity improvement and better mechanistic understanding of the state-of-the-art Ni(OH)2 catalyst. Herein, by utilizing low-temperature argon (Ar) plasma processing, tooth-wheel Ni(OH)2 nanosheets self-supported on Ni foam (Ni(OH)2-Ar) are demonstrated to have improved UOR activity compared to conventional Ni(OH)2. The theoretical assessment confirms that the edge has a smaller cation vacancy formation energy than the basal plane, consequently explaining the structural formation. Operando and quasi-operando methods are employed to investigate the dynamic evolution of the Ni(OH)2 film in UOR. The crucial dehydrogenation products of Ni(OH)5O- intermediates are identified to be stable on the etched edge and explain the enhanced UOR in the low potential region. In addition, the dynamic active sites are monitored to elucidate the reaction mechanism in different potential ranges.

Phase and crystallinity regulations of Ni(OH)2 by vanadium doping boost electrocatalytic urea oxidation reaction

Direct urea fuel cell (DUFC) and overall urea splitting system have attracted considerable attention as promising choice for energy conversion. Whereas, the anodic half reaction of electrocatalytic urea oxidation reaction (UOR) in these systems awfully limited their practical application due to the complex 6-electron transfer process. Herein, vanadium doped nickel (V-Ni(OH)2) with highly efficient electrocatalytic activity toward UOR was developed by a simple coprecipitation method. The introducing of V not only promotes the phase transforming from inactive β-Ni(OH)2 to highly active α-Ni(OH)2, but also simultaneously modulates the electron environment of Ni, facilitating high valence species Ni3+ generation in low overpotential, enhancing the electrocatalytic activity potent of each Ni3+ site and speeding up the electrocatalytic reaction. The optimal V-Ni(OH)2 catalyst exhibits a summit current density of 241 mA cm−2 at 1.6 V vs. RHE, a Tafel slope of 32.15 mV dec-1, outperforming β-Ni(OH)2 and most catalysts that tested on glassy carbon electrode. Furthermore, the assembled direct urea hydrogen peroxide fuel cell (DUPFC) offers a maximum power density of 13.4 mW cm−2 at 20 °C. This work provides an example of combing phase-regulation and electron modulation method for effective UOR electrocatalysts design.

Nickel sulphide decorated nitrogen rich ordered mesoporous carbon (NOMC) as an efficient catalyst for the electrocatalytic oxidation of urea in alkaline medium

The urea oxidation reaction (UOR), as a feasible alternative for the slow oxygen evolution reaction (OER), is recognized as an encouraging puissant approach for hydrogen generation through water splitting. The route also offers excellent potential for hydrogen production through wastewater remediation. Here, a simple synthetic strategy has been adopted to embed NiS in a nitrogen-rich stable and activated mesoporous carbon matrix (NOMC) that has been successfully exploited for UOR. The NOMC supported nickel sulfide catalyst with high electrochemically active surface area (ECSA) exhibits a very good response towards the electro-catalytic oxidation of urea in an alkaline medium with a low working oxidation potential (potential corresponding to the current density value of 10 mA/cm2 taken as a standard) of 1.34 V (vs. RHE). The introduction of heteroatom (N) to the mesoporous carbon support and subsequent incorporation of metal sulfide rather than metal oxide or metal hydroxide, as reported previously, is done purposefully to increase the electrocatalytic activity of the catalyst through the synergistic effects of charge density with carbon support. The synergism is further supported by the comparative response in urea oxidation reaction (UOR) for NiS/NOMC catalyst compared to other Ni-based catalysts like Ni(OH)2, NiS, and NiS/CMK-3, which indicates that the activity is highest for NiS/NOMC. The catalyst attains good stability in an alkaline medium. The mesoporous carbon framework (NOMC) with considerably high BET surface area, large pore volume, and interconnected ion diffusion channels accelerate the transport of electrons through the porous surface, which makes NiS/NOMC highly efficient and stable as an electrocatalyst for the oxidation of urea in comparison to its other composite catalysts in alkaline medium.

Nickel Nanocrystals Anchored Nitrogen-Doped Carbon Derived from Eggshell Membrane as an Efficient Catalyst for the Electrocatalytic Oxidation of Urea

Nickel Nanocrystals Anchored Nitrogen-Doped Carbon Derived from Eggshell Membrane as an Efficient Catalyst for the Electrocatalytic Oxidation of Urea

H2o2 Treatment Boosts Activity of Nife Layered Double Hydroxide for Electro-Catalytic Oxidation of Urea

H2o2 Treatment Boosts Activity of Nife Layered Double Hydroxide for Electro-Catalytic Oxidation of Urea

H2o2 Treatment Boosts Activity of Nife Layered Double Hydroxide for Electro-Catalytic Oxidation of Urea

H2o2 Treatment Boosts Activity of Nife Layered Double Hydroxide for Electro-Catalytic Oxidation of Urea

Recent advances in the pre-oxidation process in electrocatalytic urea oxidation reactions.

The electrocatalytic urea oxidation reaction (UOR) has attracted substantial research interests over the past few years owing to its critical role in coupled electrochemical systems for energy conversion, for example, coupling with the hydrogen evolution reaction (HER) to realize urea-assisted hydrogen production and assembling direct urea fuel cells (DUFC) by coupling with the oxygen reduction reaction (ORR). The UOR process has been proved to be a two-step process which involves an electrochemical pre-oxidation reaction of the metal sites and a subsequent chemical oxidation of the urea molecules on the as-formed high-valence metal sites. Hence, designing advanced (pre-)catalysts with a boosted pre-oxidation reaction is of great importance in improving the UOR performance and thus accelerating the coupled reactions. In this feature article, we discuss the significant role of the pre-oxidation process during the urea electro-oxidation reaction, and summarize detailed strategies and recent advances in promoting the pre-oxidation reaction, including the modulation of the crystallinity, active phase engineering, defect engineering, elemental incorporation and constructing hierarchical nanostructures. We anticipate that this feature article will offer helpful guidance for the design and optimization of advanced (pre-)catalysts for UOR and related energy conversion applications.

CeO2 modified Ni-MOF as an efficient catalyst for electrocatalytic urea oxidation

The development of cost-efficient electrocatalysts for urea oxidation reaction (UOR) is a challenge due to the slow kinetics. In this work, we demonstrated a one-pot hydrothermal synthetic method to fabricate CeO2 modified Ni-MOF nanosheets. When evaluted as UOR catalysts, the 3% CeO2/Ni-MOF possesses outstanding catalytic activity, achieving a current density of 10 mA cm−2 at a low potential of 1.356 V with a small Tafel slope of 13.83 mV dec−1. It is considered that the unique interactions between CeO2 nanoparticles (NPs) and Ni-MOF nanosheets (NSs) play the significant role in the enhancement of the catalytic performance by inducing the formation of abundant defects and optimized surface states.

Metal-Organic Frameworks Offering Tunable Binary Active Sites toward Highly Efficient Urea Oxidation Electrolysis.

Electrocatalytic urea oxidation reaction (UOR) is regarded as an effective yet challenging approach for the degradation of urea in wastewater into harmless N2 and CO2. To overcome the sluggish kinetics, catalytically active sites should be rationally designed to maneuver the multiple key steps of intermediate adsorption and desorption. Herein, we demonstrate that metal-organic frameworks (MOFs) can provide an ideal platform for tailoring binary active sites to facilitate the rate-determining steps, achieving remarkable electrocatalytic activity toward UOR. Specifically, the MOF (namely, NiMn0.14-BDC) based on Ni/Mn sites and terephthalic acid (BDC) ligands exhibits a low voltage of 1.317 V to deliver a current density of 10 mA cm−2. As a result, a high turnover frequency (TOF) of 0.15 s−1 is achieved at a voltage of 1.4 V, which enables a urea degradation rate of 81.87% in 0.33 M urea solution. The combination of experimental characterization with theoretical calculation reveals that the Ni and Mn sites play synergistic roles in maneuvering the evolution of urea molecules and key reaction intermediates during the UOR, while the binary Ni/Mn sites in MOF offer the tunability for electronic structure and d-band center impacting on the intermediate evolution. This work provides important insights into active site design by leveraging MOF platform and represents a solid step toward highly efficient UOR with MOF-based electrocatalysts.

Hierarchical Ni-Mo-P nanoarrays toward efficient urea oxidation reaction.

The urea oxidation reaction (UOR), which possesses a low theoretical potential and superior kinetics, is an attractive substitute for the anodic oxygen evolution reaction (OER) in overall water splitting; however, the implementation of hydrogen production in overall urea splitting is impeded by the deficiency of highly efficient, durable and cost-effective catalysts. Herein, we fabricated an Ni2P-MoP2 heterostructure with a hierarchical structure grown on carbon paper (Ni-Mo-P/CP), which exhibited robust activity and outstanding durability for the electrocatalytic oxidation of urea. The Ni-Mo-P/CP catalyst possessed an ultralow potential of 1.39 V to obtain the current density of 100 mA cm-2, small Tafel slope (27 mV dec-1) and long-term durability with almost no decay within 15 h. The experimental characterization revealed that the optimized electronic structure and the synergistic effect of abundant exposed active sites in the Ni-Mo-P/CP catalyst contribute to the efficient UOR catalytic activity. This work enriches the candidate catalysts for the UOR and promotes the industrial development of hydrogen production.

Regulating the pyrolysis process of cation intercalated MnO2 nanomaterials for electrocatalytic urea oxidation performance.

Exploring an efficient way to enhance electron/ion transport behavior of nanomaterials plays an important role in the study of energy storage & conversion. However, the evolution rules of lattice and electronic structure during the pyrolysis process of low-dimensional nanomaterials, which further regulate its electron/ion transport properties, have not been effectively elucidated. Here we study the pyrolysis process of cation intercalated MnO2 as a case for realizing optimized electron/ion transport behavior. In our case, thermogravimetry-mass spectrometry (TG-MS) was adopted for tracking the remaining products in pyrolysis and decomposition products, further finding out the evolution law of the manganese-oxygen polyhedron structure during the pyrolysis. Moreover, the internal relations between the crystal structure and the electronic structure during the pyrolysis process of low-dimensional manganese oxide are revealed by fine structure characterization. As expected, partially treated 2D MnO2 nanosheets with controlled pyrolysis displays ultrahigh UOR performance with the overpotential of 1.320 V vs. RHE at the current density of 10 mA cm-2, which is the best value among non-nickel-based materials. We anticipate that studying the mechanism of the pyrolysis process has important guiding significance for the development of high electron/ion transport devices.

Synergistic doping and structural engineering over dendritic NiMoCu electrocatalyst enabling highly efficient hydrogen production.

The development of non-precious metal electrocatalysts with remarkable activity is a major objective for achieving high-efficiency hydrogen generation. Here, a trimetallic electrocatalyst with a dendritic nanostructure, which is denoted as NiMoCu-NF, was fabricated on nickel foam via a gas-template electrodeposition strategy. By virtue of the metallic doping and structural optimization, NiMoCu-NF exhibits superior HER electrocatalytic activity with an overpotential of 52 mV at 10 mA cm-2. Additionally, the NiMoCu-NF-derived nickel-based (oxy)hydroxide species in the oxidation operating state deliver considerable electrocatalytic urea oxidation reaction (UOR) performance to match the efficient H2 generation, with a low voltage of 1.54 V to realize overall electrolysis at 50 mA cm-2. Impressively, combined experimental and simulation analysis demonstrate that the NiMoCu-NF with a favorable 3D nanostructure feature effectively regulates the heterogeneous interface states, inducing a "Gas Microfluidic Pumping" (GMP) effect that improved electron-mass transfer properties to accelerate the electrocatalytic reaction kinetics of either the HER or UOR.

Interface enables faster surface reconstruction in a heterostructured Co–Ni–S electrocatalyst towards efficient urea oxidation

The electrocatalytic urea oxidation reaction (UOR) can be utilized as an alternative anodic reaction for water electrolysis to provide more economic electrons and high-efficiency H2 production.

Synthesis of hierarchical nickel sulfide nanotubes for highly efficient electrocatalytic urea oxidation

It is a challenge to prepare high-efficiency and inexpensive electrocatalysts toward urea oxidation reaction (UOR). Herein, we report the fabrication of NiS nanotubes with hierarchical sheet-like surface morphology via a novel template-directed hydrothermal reaction as efficient UOR electrocatalyst. The unique hollow structure of NiS nanotubes provides the exposure of more active sites and excellent electron/mass transport properties, ensuring a superior UOR performance. The NiS nanotubes catalyst shows a very low potential at around 1.39 V vs. RHE at 100 mA cm−2 in 1 M KOH/0.33 M urea solution. And the UOR current density of the catalyst at 1.4 V vs. RHE reaches 135 mA cm−2, representing a superior UOR performance. The NiS nanotubes catalyst also possesses an excellent operational stability. Furthermore, a two-electrode urea-assisted overall water splitting (OWS) device assembled with NiS nanotubes as anode and Pt/C as cathode delivers a working voltage of 1.445 V to attain 10 mA cm−2, which is 188 mV less than that for the urea-free OWS electrolyzer, demonstrating its possibility to be applicable for energy efficient hydrogen production. This study provides a rationale to develop high-efficiency non-precious metal-based UOR catalysts for the efficient assistance of hydrogen fuel generation.

Facile synthesis of amorphous nickel iron borate grown on carbon paper as stable electrode materials for promoted electrocatalytic urea oxidation

The development of greatly stable and cost-effective electrocatalysts for urea electro-oxidation reactions (UERs) is urgent and challenging for promoting urea removal in the wastewater and advanced energy conversion devices. We demonstrated that nickel-iron borate (NiFe-B) electrocatalysts supported on carbon paper (CP) for UERs through a one-pot solvothermal method. NiFe-B electrocatalysts were obtained with numerous Ni/Fe molar ratios in the precursors, and the physicochemical features of the NiFe-B were examined by X-ray diffraction, scanning and transmission electron microscope, and X-ray photoelectron spectroscopy. The optimized NiFe-B/CP exhibited a low onset potential (Eonset = 0.287 V vs. SCE) with a Tafel slope of 27.9 mV/dec on CP, demonstrating much greater performance UERs. Furthermore, the NiFe-B/CP catalysts have shown a superior activity for the UERs in alkaline solution and exhibit more than two-fold enhancement in activity than Ni-B. Facile, cost-effective fabrication and highly efficient urea oxidation create the NiFe-B electrodes as attractive materials for UERs.

In situ-grown Co3O4 nanorods on carbon cloth for efficient electrocatalytic oxidation of urea

In situ-grown Co3O4 nanorods on carbon cloth for efficient electrocatalytic oxidation of urea

Interfacial engineering of the NiSe2/FeSe2 p-p heterojunction for promoting oxygen evolution reaction and electrocatalytic urea oxidation

Heterogeneous electrocatalysis usually involves the charge transfer between the surface of electrocatalysts and corresponding reactants. Thus, modulating the surface electron density of electrocatalysts is an effective strategy to boost the electrocatalytic activity of targeted reactions. Herein, the NiSe2/FeSe2 p-p heterojunction is constructed via a simple selenization method for both oxygen evolution reaction (OER) and urea oxidation reaction (UOR). The designed NiSe2/FeSe2 electrocatalyst exhibits a superior activity towards OER, which only requires a low overpotential of 256 mV to reach a current density of 10 mA cm−2, and surpasses other selenides and even the state-of-the-art RuO2. Impressively, when employed as the UOR electrode, the NiSe2/FeSe2 heterojunction needs only 127 mV overpotential at 50 mA cm-2, remarkably superior to other selenides and confirming the less energy consumption for UOR. The comprehensive analysis demonstrates that the well-designed built-in electric field at the heterointerface of NiSe2/FeSe2 p-p heterojunction due to the difference of energy levels can expedite the charge transfer and thus strengthen the conductivity of heterojunction electrocatalyst. Moreover, the self-driven electron transfer across the NiSe2/FeSe2 heterointerface can induce local charge redistribution at the interface region, which is beneficial for the adsorption of OH− and urea owing to the electrostatic interaction. Therefore, the designed NiSe2/FeSe2 p-p heterojunction with regulated electronic structure displays extraordinary electrocatalytic activity for both the OER and UOR. This study demonstrates a novel strategy to manipulate the surface/interface charge states of electrocatalysts for improving the catalytic activity of OER and UOR, and provides new guidelines for exploring other superior electrocatalysts.

Finite Element Method Study of Nanostructured Metal Oxide Based on NiO for Nonenzymatic Urea Sensors

Urea electrooxidation has attracted increasing attention because urea is an essential biomarker for diagnosing kidney conditions. Most urea sensors are based on the enzyme; however, enzyme-based sensors have a moderately complicated assembling method [1] due to poor stability. Different from the bulk diffusion of urea in the enzymatic urea oxidation [2], the nonenzymatic urea oxidation has reactions between the reductive and oxidative at the electrode surface [3]. Moreover, in order to use nonenzymatic urea sensors in a biomedical application area, high conductivity and catalytic activities are required. Therefore, a study of nonenzymatic urea sensor on a nanostructured electrode is of substantial interest.For urea detection, various metal oxides, such as ZnO [4], CuO [5], and NiO [6], have been broadly proposed. Practically, NiO catalysts were studied extensively for urea electrooxidation due to successful long-term operation [7]. Typical nonenzymatic catalysts for urea electrooxidation mainly focused on designing new nanostructures and maximizing their catalytic ability. However, quantitative models integrating the physical, chemical, and geometrical design properties still need improvement to develop sensor devices. The urea reaction occurs on the surface of nanostructured metal oxide. Thus, the effect of electrode geometry on the electrochemical reactions is motivated to explore urea sensors application.In the present study, we studied three different NiO structures such as nanorods, nanoflakes, and nanoparticles, for the nonenzymatic electrochemical sensor. Additionally, we developed a new analytical model to understand the nonenzymatic urea sensor using the finite element method. To further adjust the model, the morphology and the composition of the NiO catalysts were investigated using transmission electron microscopy, scanning electron microscopy, and X-ray photoelectron spectroscopy. The NiO catalysts showed remarkable electrochemical achievement with acceptable linear sensitivity and selectivity to urea electrooxidation. Comprehensive information of the modeling concerning NiO as a catalyst in the nonenzymatic urea sensor will be given.References FATEMA, Kamrun Nahar, et al. “New Design of Active Material Based on YInWO4-G-SiO2 for a Urea Sensor and High Performance for Nonenzymatic Electrical Sensitivity.” ACS Biomaterials Science & Engineering, 2020.Debata, Suryakanti, et al. "Design of CdV2O4-V6O13 micro flowers for non-enzymatic electrochemical detection of urea." In AIP Conference Proceedings, vol. 2115, no. 1, p. 030058. AIP Publishing LLC, 2019.YOON, Jaesik, et al. “Silver-Nanoparticle-Decorated NiOOH Nanorods for Electrocatalytic Urea Sensing.” ACS Applied Nano Materials, 2020, 3.8: 7651-7658.YOON, Jaesik, et al. “Ag/ZnO Catalysts with Different ZnO Nanostructures for Non‐enzymatic Detection of Urea.” Electroanalysis, 2019, 31.1: 17-21.Goda, M. A., et al. “Enhanced Electrocatalytic Oxidation of Urea at CuOx-NiOx Nanoparticle-Based Binary Catalyst Modified Polyaniline/GC Electrodes.” Journal of The Electrochemical Society, 2020 167(6), 064522.Tyagi, Manisha, et al. "NiO nanoparticle-based urea biosensor." Biosensors and Bioelectronics 2013, 41:110-115.BARAKAT, Nasser AM, et al. “Influence of nitrogen doping on the electrocatalytic activity of Ni-incorporated carbon nanofibers toward urea oxidation.” International Journal of Hydrogen Energy, 2017, 42.34: 21741-21750.