Electrocatalytic Oxidation Of Urea Research Articles

Interlayer Effect in NiCo Layered Double Hydroxide for Promoted Electrocatalytic Urea Oxidation

Urea electrolysis is a promising route to utilize urea-rich wastewater as an energy source to produce hydrogen on the cathode or generate electricity through a direct urea fuel cell, which offers g...

Ultrathin nickel hydroxide nanosheets with a porous structure for efficient electrocatalytic urea oxidation

Porous β-Ni(OH)2 nanosheets with ultrathin thickness are prepared through a microwave-assisted synthesis strategy and used as a platform to promote the electrocatalytic urea oxidation reaction.

Hierarchical NiCo2O4 nanowire array supported on Ni foam for efficient urea electrooxidation in alkaline medium

Abstract NiCo2O4 nanowire arrays grown on Ni foam (NiCo2O4/NF) are synthesized by a simple template-free hydrothermal route followed by a thermal treatment in the air at 400 °C. The as-prepared Ni foam substrate exhibits homogeneous and porous nanowire arrays, which providing a number of active sites and electronic transmission channels for urea electrooxidation. The electroactivity of NiCo2O4/NF electrode toward the oxidation of urea in alkaline solution is evaluated using cyclic voltammetry (CV), chronoamperometry (CA) and electrochemical impedance spectroscopy (EIS) measurements. Results show that the as-obtained electrode delivers an outstanding electrocatalytic activity and stability for urea electrooxidation. The NiCo2O4/NF electrode delivers a low open potential at 0.19 V versus Ag/AgCl with a corresponding current density of 570 mA cm−2 in 5 mol L−1 KOH and 0.33 mol L−1 urea electrolytes. Meanwhile, detailed investigation is made for the electrocatalytic oxidation of urea by varying several reaction parameters, such as scan rate, urea and KOH concentrations. Benefiting from the unique structure and synergistic effects of Ni and Co, the NiCo2O4/NF electrode exhibit superior electrocatalyst activity and is considered to be a promising candidate catalysis material for direct urea fuel cell.

Mn2O3/Ag Nanoflakes as an Effective Electroscatalyst for Urea Oxidation in Alkaline Medium

AbstractIn this study, highly crystalline Ag-doped Mn2O3 nanoflakes were synthesized by a sol-gel process and used as an effective electrocatalyst for urea electrooxidation in alkaline-media fuel cells. Scanning electron microscope (SEM), X-ray diffraction (XRD), transmission electron microscope (TEM) and energy dispersive spectroscopy (EDS) were applied to characterize the structure and the morphology of the final product. The electrocatalytic performances were investigated by cyclic voltammetry (CV) and chronoamperometry (CA) tests.The prepared nanocatalyst shows a distinct electrocatalytic activity toward urea oxidation. The introduced Ag-doped Mn2O3 reveals a good stability at various applied voltages. The enhanced electrocatalytic oxidation of urea using Ag-doped Mn2O3 nanoflakes reveals a great potential for future applications in hydrogen production, remediation of urea-rich wastewater, and fuel cells.

In situ growth of single-layered α-Ni(OH)2 nanosheets on a carbon cloth for highly efficient electrocatalytic oxidation of urea

The electrochemical urea oxidation reaction (UOR) is useful for the simultaneous elimination of urea-rich wastewater and generation of hydrogen.

Oxygen Vacancies Confined in Nickel Molybdenum Oxide Porous Nanosheets for Promoted Electrocatalytic Urea Oxidation

The direct urea fuel cell (DUFC), as an efficient technology for generating power from urea, shows great potential for energy-sustainable development but is greatly hindered by the slow kinetics of the urea oxidation reaction (UOR). Herein, we highlighted a defect engineering strategy to design oxygen vacancy-rich NiMoO4 nanosheets as a promising platform to study the relationship between O vacancies and UOR activity. Experimental/theoretical results confirm that the rich O vacancies confined in NiMoO4 nanosheets successfully bring synergetic effects of higher exposed active sites, faster electron transport, and lower adsorption energy of urea molecules, giving rise to largely improved UOR activity. As expected, the r-NiMoO4/NF 3D electrode exhibits a higher current density of 249.5 mA cm–2, which is about 1.9 and 5.0 times larger than those of p-NiMoO4/NF and Ni-Mo precursor/NF at a potential of 0.6 V. Our finding will be a promising pathway to develop non-noble materials as highly efficient UOR catalysts.

Electrocatalytic oxidation of urea in alkaline solution using nickel/nickel oxide nanoparticles derived from nickel-organic framework

Abstract Nickel-organic framework (NiOF) compound with layered structure was prepared by solvothermal synthesis using nickel chloride and bezenedicarboxylic acid precursors. NiOF could be converted into nickel with a face-centered cubic structure and nickel oxide with a cubic rock-salt crystal structure after heating above 425 °C in air atmosphere. The organic units played a key role in the formation of well-dispersed nickel/nickel oxide nanoparticles. Primary particle size could be decreased by lowering the calcination temperature. Electrophoresis allowed for depositing a thin layer of nickel/nickel oxide nanoparticles on the skeleton of macroporous nickel foam (NF) as a catalyst electrode for electrooxidation of urea. Nickel/nickel oxide nanoparticles derived from NiOF at 425 °C possessed large amounts of redox active sites (Ni2+/Ni3+), and thus was capable of enhancing the current density and efficiency in urea electrolysis. NF substrate with unique macroporous conductive structure exhibited electrocatalytic behavior towards urea electrolysis and allowed for rapid transport of electron, electrolyte, and gaseous products. Therefore, coating of nickel/nickel oxide nanoparticles on NF provided a possible way for further enhancing the electrocatalytic ability of electrode in urea electrolysis, making it favorable for large-scale applications.

A comprehensive study on electrocatalytic current of urea oxidation by modified carbon paste electrode with Ni(II)-clinoptilolite nanoparticles: Experimental design by response surface methodology

Abstract In this work, the electrocatalytic oxidation of urea in alkaline medium was studied by the modified carbon paste electrode (CPE) with clinoptilolite nanoparticles (CNP) ion-exchanged with Ni(II) cations (Ni(II)-CNP/CPE) in cyclic voltammetry technique (CV). X-Ray diffraction (XRD), Scanning Electron Microscopy-Energy Dispersive X-Ray spectroscopy (SEM-EDX) and FT-IR methods were used for characterization of the samples. Interactions of the experimental factors were studied by designing the experiments via response surface methodology (RSM). The proposed electrode showed reasonable electrocatalytic effect in oxidation of urea, so the oxidation of urea on surface of the proposed electrode had lower overvoltage about 700 mV less positive than the conventional Pt electrodes. Surface coverage concentration of the electrode was about 3.97 × 10− 6 mol Ni(OH)2 cm− 2. The apparent charge transfer rate constant and the cathodic charge transfer coefficient for the modified electrode were respectively obtained as 0.39 s− 1 (ks) and 0.18 (αc) in the absence of urea, while αa was 0.7 in the presence of urea.

Highly efficient electrocatalytic oxidation of urea on a Mn-incorporated Ni(OH)2/carbon fiber cloth for energy-saving rechargeable Zn-air batteries.

A Mn-incorporated Ni(OH)2/carbon fiber cloth (Mn-Ni(OH)2/CFC) fabricated via a room-temperature solution route exhibited superior electrocatalytic activities of the oxygen reduction and urea oxidation reactions, delivering 12-21% energy saving in the charging process of Mn-Ni(OH)2/CFC assembled Zn-air batteries in the presence of 0.5 M urea compared to the battery without urea.

Two-dimensional metal-organic frameworks with high oxidation states for efficient electrocatalytic urea oxidation.

A two-dimensional metal-organic framework (MOF) comprising nickel species and an organic ligand of benzenedicarboxylic acid is fabricated and explored as an electrocatalyst for urea oxidation reaction (UOR). The excellent UOR performance is found to be partially due to the high active site density of the two-dimensional MOF, and largely because of the high oxidation state of the nickel species.

Improved Electrocatalytic Oxidation of Urea Using Ru-Ni Binary Nanoparticles Prepared By an Ionic Liquid/Metal Sputtering Technique

Introduction Direct urea fuel cells are attracting as next generation power sources due to the high energy density, safety, and ease of transportation of urea in comparison with other candidate sources for fuel cells, such as hydrogen, alcohols and ammonia. Botte and co-workers reported that nickel electrodes exhibited electrocatalytic activity for urea oxidation in basic aqueous solution.[1] However further improvement in stability and activity for catalysts is necessary to achieve practical use. Recently we have reported the facile preparation of metal and alloy nanoparticles in ionic liquids without additional stabilizing agents using metal sputter deposition technique.[2]The extremely low vapor pressure of ionic liquids enables the sputter deposition of metal species onto the ionic liquids under reduced pressure. Noble metal nanoparticles of several nanometers in size, such as Au, Pd, and Pt, were successfully prepared by sputtering the corresponding metal targets, while simultaneous sputter deposition of different metals produced alloy nanoparticles such as AuPd and AuPt. Alloy nanoparticles exhibited unique physicochemical properties distinct from those of monometallic counterparts, and their catalytic activities could be modified by the control of chemical composition of nanoparticles. Here we report the preparation of Ru-Ni binary nanoparticles by sequential sputter deposition of Ru and Ni onto ionic liquids followed by heat treatment. Furthermore the electrocatalytic activity of thus-obtained nanoparticles is investigated for urea oxidation in alkaline media. Experimental Ru-Ni binary nanoparticles were synthesized by the sequential sputter deposition of Ru and Ni metals onto ionic liquids of 1-ethyl-3-methylimidazolium tetrafuloroborate using a sputter coater (SC-701HMCII, Sanyu Electron). A portion of acetonitrile solution dispersed with carbon black (CB) particles was mixed with thus-obtained ionic liquids, followed by heat treatment at 300 ˚C for 30 min. Thus-obtained Ru-Ni nanoparticles-immobilized CB particle catalyst (Ru-Ni/CB) were isolated by centrifugation. The Ni/Ru ratio in the catalyst was controlled by changing the amount of Ru sputter-deposited in the ionic liquid. Nanoparticles of Ru and Ni, loaded on CB in a similar manner, were also prepared for comparison. The electrocatalytic activity for urea oxidation was investigated with use of grassy carbon electrodes modified with Ru-Ni/CB catalyst particles in 0.1 mol dm-3 NaOH aqueous solution containing 0.1 mol dm-3 urea. Results and discussions TEM observation of Ru-Ni/CB revealed that small Ru-Ni binary nanoparticles with average diameter of 3.9 ± 2.1 nm were densely immobilized on the surface of CB particles without formation of large aggregation as shown in the inset of Fig. 1. The chemical condition of particles loaded on CB was investigated by XPS. Ni/CB showed a single peak of Ni 2p at 856.1 eV attributable to Ni2+, indicating that Ni was completely oxidized during preparation procedure of catalyst. In contrast, the Ni 2p signals of Ru-Ni/CB appeared at 854.2 and 860.1 eV, which were assigned to Ni0 and Ni3+, respectively. This suggests that Ni oxidation was partially prevented in Ru-Ni/CB probably due to the electronic interaction between Ni and Ru atoms. Figure 1 shows cyclic voltammograms of Ru-Ni/CB, Ni/CB, and Ru/CB for urea oxidation in 0.1 mol dm-3NaOH aqueous solution. As reported previously, Ni/CB exhibited the electrocatalytic activity for urea oxidation, in which anodic current for urea oxidation was increased at the potential more positive than 0.5 V vs Ag/AgCl, though no current was observed for Ru/CB. On the other hand, urea oxidation also occurred with use of Ru-Ni/CB at the potential more positive than 0.5 V vs Ag/AgCl, the intensity being about 2 times larger than that of Ni/CB at a constant potential. These results indicated that the electrocatalytic activity for urea oxidation was higher for Ru-Ni binary particles than pure Ni particles, in spite that Ru particles had no activity. The chemical composition of Ru-Ni/CB catalyst was found to influence the catalytic activity: Volcano-type dependence was observed between Ru content in Ru-Ni/CB and the current density at 0.6 V vs. Ag/AgCl. Consequently, we concluded that electrocatalytic activity for urea oxidation of Ni particles was improved by preparing Ru-Ni binary nanoparticles in which Ru and Ni were probably mixed in atomic or nanometer scales. REFERENCES [1] Botte, et al., Electrochimica Acta, 2012, 81, 292. [2] M. Hirano, et al., Phys. Chem. Chem. Phys., 2013, 15, 7286. Figure 1

Impact of the alkali cation on the electrocatalytic oxidation of urea and benzyl alcohol on nickel electrode

Abstract The effect of electrolyte alkali metal cations (Li + , Na + , or K + ) on the electro-oxidation of urea and benzyl alcohol on NiOOH catalyst has been investigated by means of cyclic voltammetry and chronoamperometry in the presence of an electrolyte containing LiOH, NaOH, or KOH. The catalytic activity toward the electro-oxidation of urea and benzyl alcohol was found to increase in the sequence Li + + + . This activity's difference is partly caused by different surface blockage abilities by OH–M + (H 2 O) x (M: Li, Na, K) clusters, which is similar to many electrocatalytic reactions on Pt reported previously, additionally, incorporation of various cations to the catalyst may induce the activities difference as well.

Easy-to-prepare electrochemical platform composed of ionic liquid-Ni(II)-graphite composites: laboratory study on electrochemical oxidation of urea, alcohols, and glucose

Abstract Ni(II) was introduced into four room-temperature ionic liquids (RTILs), namely 1-butyl-3-methylimidazolium salicylate (BMI-SAL), BMI hexafluorophosphate (BMI-PF 6 ), 1-butyl-1-methylpyrrolidinium dicyanamide (BMP-DCA), and BMP bis((trifluoromethyl)sulfonyl) imide (BMP-TFSI), via the addition of NiCl 2 or the anodic dissolution of Ni metal. The RTILs containing different Ni(II) species were mixed with pure and fine graphite (GP) powder to form RTIL/Ni(II)/GP composites, which were used to prepare composite electrodes for the electrocatalytic oxidation of urea, alcohols (methanol, ethanol, isopropanol, butanol, and glycerol), and glucose. Ni(II) produced from the anodic dissolution of Ni metal in BMP-TFSI showed the best activity. The BMP-TFSI/Ni(II) anodization /GP composite thus has potential as an easy-to-prepare electrochemical platform for the electrochemical oxidation of the above-mentioned compounds. The oxidation and determination of urea using the BMP-TFSI/Ni(II) anodization /GP composite electrode was thoroughly studied. A very high sensitivity of 517 μA·mM −1 ·cm −2 was obtained. This electrode also showed good stability during the anodic electrolysis of the aforementioned compounds, indicating that it may be appropriate as an anode for the electrolysis of urea, alcohols, and glucose.

Preparation of the carboxylic acid-functionalized graphene oxide/gold nanoparticles/5-amino-2-hydroxybenzoic acid as a novel electrochemical sensing platform

The carboxylic acid-functionalized graphene oxide/gold nanoparticles modified glassy carbon electrode has been utilized as a platform to immobilize 5-amino-2-hydroxybenzoic acid (mesalazine). The su rface structure and composition of the sensor were characterized by scanning electron microscopy. Electrocatalytic oxidation of urea on the surface of modified electrode was investigated with cyclic voltammetry, electrochemical impedance spectroscopy, and hydrodynamic voltammetry methods. The cyclic voltammetric results indicated the ability of carboxylic acid-functionalized graphene oxide gold nanoparticles modified glassy carbon electrode to catalyze the oxidation of urea. In addition, the modified electrode has short response time, low detection limit, high sensitivity, and low operation potential. Some kinetic parameters, such as the electron transfer coefficient, diffusion coefficient, and catalytic rate constant of the catalytic reaction were calculated. A sensitive amperometric method was proposed for determination of urea with advantages of fast response and good reproducibility.

Mesoporous NiCo2O4 Nanosheets Grown on Stainless Steel Meshes As Binder Free Electrodes for Urea Electrolysis

To alleviate the requirement of non-renewable fossil fuels and satisfy the increasing global energy demands, it is important to seek and develop the sustainable and environmental friendly energy sources. Recently, urea (CO(NH2)2) has been demonstrated as a hydrogen carrier for long-term sustainable energy supply due to its intrinsic properties, such as non-toxic, non-flammable, and easy storage.1-3 Urea electrolysis with an inexpensive bulk nickel catalyst showed great promising in directly converting urea into valuable energy product (H2) and a non-toxic product (N2).1 Nanostructured nickel catalysts enhanced the electrocatalytic oxidation of urea due to their large surface areas and controlled low dimensional structures.4 However, the introduction of polymer binders for the nanostructured nickel powder based electrode preparation unavoidably decreased the conductivity of catalysts and thus reduced the electrocatalytic performance of urea electrolysis. In addition, previous research showed that the incorporation of cobalt into nickel catalysts decreased the overpotential of urea oxidation and improved the reaction rate considerably.5 Nickel cobaltite (NiCo2O4) is well-known electrode materials for supercapacitors and lithium batteries and nanostructured NiCo2O4 exhibited their improved electrochemical performance.6,7 Therefore, it’s interesting to extend the applications of nanostructured NiCo2O4 to urea electrolysis for hydrogen production. Within this context, this work focuses on directly synthesizing mesoporous NiCo2O4 nanosheets on conductive substrates, such as stainless steel mesh, and using it as binder free electrode for urea electrolysis. TEM image (Figure 1 a) shows the morphology of two dimensional NiCo2O4 nanosheets. XRD pattern (Figure 1 b) shows the crystalline structure of NiCo2O4 nanosheets. Figure 1 d (curve 2) shows a strong oxidation current starting at ca. 0.38 V vs. Hg/HgO when 0.33 M urea was present in the KOH solution. As a comparison, the urea oxidation at the bulk Ni(OH)2 powder electrode (Figure 1 c) started at ca. 0.46 V vs. Hg/HgO. Thus the NiCo2O4 nanosheets electrode reduced the onset potential of the oxidation process of urea by 80 mV. Furthermore, the NiCo2O4 nanosheet electrode sharply increased the urea oxidation current density compared to bulk Ni(OH)2electrode. Figure 1. (a) TEM image of mesoporous NiCo2O4 nanosheets; (b) XRD pattern of NiCo2O4; (c) Cyclic voltammograms of bulk Ni(OH)2 electrode in 5 M KOH solution in the absence (curve 1) and presence (curve 2) of 0.33 M urea. (d) CV of NiCo2O4 nanosheet electrode in 5 M KOH solution in the absence (curve 1) and presence (curve 2) of 0.33 M urea. The scan rate was 10 mVs-1.

Hydrothermal growth of vertically-aligned ordered mesoporous nickel oxide nanosheets on three-dimensional nickel framework for electrocatalytic oxidation of urea in alkaline medium

Abstract Vertically-aligned α-Ni(OH)2 nanosheets are homogeneously covered on three-dimensional (3D) macroporous Ni foam and stainless steel (SS) sheet by a simple hydrothermal synthesis. After annealing at 300 °C, most of the α-Ni(OH)2 is transformed to cubic NiO. The NiO nanosheets exhibit ordered mesoporous structure. Electrolysis of urea is analyzed by cyclic voltammetry and potential step chronoamperometry in 1 M KOH electrolyte with 0.33 M urea. The electrocatalytic performance of NiO electrodes depends strongly on their configuration and substrate. Vertically-aligned NiO nanosheets favor the electrolysis of urea because they can provide more catalytic sites than the NiO powder with aggregated nanosheets. In addition, the large open space between vertically-aligned NiO nanosheets expedites the transport of electrolyte, urea, and gases. 3D macroporous Ni foam substrate is very helpful to the electrolysis of urea which allows for fast electron conduction, leading to a decrease of overpotential and the increase of oxidation current density. Consequently, the Ni foam-supported mesoporous NiO nanosheets can offer a much better electrocatalytic performance than SS-supported mesoporous NiO nanosheets and powder during electrolysis of urea.

Experimental Investigation of Potential Oscillations during the Electrocatalytic Oxidation of Urea on Ni Catalyst in Alkaline Medium

For the first time, potential oscillations are observed during the electrochemical oxidation of urea on Ni catalyst in alkaline medium. Electrochemical measurements, in combination with in situ time-resolved surface enhanced Raman (SER) spectroscopy studies, revealed that the potential oscillations might be caused by the periodic reduction and oxidation of the electrochemically active NiOOH catalyst to its inactive Ni(OH)2 state and vice versa. Cyclic voltammetry and rotating disc electrode voltammetry suggests that mass transfer of urea to the double layer region due to local convection caused by oxygen evolution reaction does not play a role in the potential oscillation mechanism.

Nickel nanowires as effective catalysts for urea electro-oxidation

Abstract Urea electrolysis catalyzed by bulk nickel catalysts has revealed great potential in hydrogen production and remediation of urea-rich wastewater. In this study, one-dimensional (1-D) nickel nanowires electrocatalyts (NNE) were developed to enhance the electrocatalytic oxidation of urea. The nanowires were fabricated by electrodeposition assisted with an anodic aluminium oxide (AAO) template. The NNE exhibit higher electrocatalytic activity and higher current efficiency of urea electrolysis than that of bulk nickel film electrocatalysts (NFE). The as-prepared NNE represent a new class of robust catalysts for urea electrolysis, which demonstrates promise for future applications in hydrogen production, fuel cells, and wastewater remediation.

ECS Student Achievement Award of the IEEE Division Electrochemical Oxidation of Urea on Nickel Catalyst in Alkaline Medium: Investigation of the Reaction Mechanism

Abundantly available alternate clean and inexpensive energy sources that are independent of fossil fuels have been sought after due to low or no net CO2 emission. Urea rich wastewater, the product of human/animal excretion, which is copiously available on earth, has been identified as alternate fuel for H2production in alkaline medium. The urea in wastewater will decompose naturally to ammonia that will again break down to nitrates and nitrites, thus polluting the environment. The available de-nitrification technologies are expensive, whereas urea electrolysis can produce hydrogen from wastewater thus removing urea from water.Botte1 and Boggs2 had successfully demonstrated that urea/urine could be electrochemically oxidized to N2 and CO2 at the anode and H2 at the cathode with the aid of a low-cost transition metal catalyst, nickel, in alkaline medium2. Pure water can be obtained as a by-product of the urea electrolysis process.The conventional way of H2 production is from alkaline electrolysis of water. The standard cell potential at which urea electrolysis occurs is 0.37 V, whereas the standard cell potential for the alkaline water electrolysis is 1.23 V. When compared with the water electrolysis technology, urea electrolysis requires thermodynamically 75 % less energy to produce H2.Catalyst development plays an important role in the electro-oxidation of urea in alkaline medium. Though various authors have demonstrated that catalysts like Ni-Co3, 2D Ni(OH)2 nanosheets4 and Pt5 can be used to electrochemically oxidize urea in alkaline medium,the work related to identifying the kinetics and the underlying reaction mechanism is none. A comprehensive understanding of the reactions, intermediates and phenomenon associated with the electrocatalytic oxidation of urea in alkaline medium need to be addressed to help design and optimize the catalyst.Within this context, the research objective of the project is to develop a reaction mechanism scheme for the electro-oxidation of urea on Ni catalyst, experimentally. Also, the kinetic parameters like reaction order, diffusion co-efficient, rate constants, etc. will be deduced for the electro-oxidation reaction of urea on Ni electrode. Various electrochemical techniques like cyclic voltammetry (CV), rotating disk electrode voltammetry (RDE), electrochemical impedance spectroscopy (EIS), galvonodynamic and galvanostaic experiments will be employed. To get further insight into the mechanism, the electrochemical data will be supported by surface characterization techniques such as in-situ surface enhanced Raman spectroscopy (SERS) and in-situFourier Transform Infrared Spectroscopy (FTIR) will also be employed to understand the electrochemical oxidation mechanism.

Enhanced electrocatalytic oxidation of urea based on nickel hydroxide nanoribbons

One-dimensional nickel hydroxide nanoribbons with thickness of 15–20 nm and length up to several micrometers were synthesized through a simple template-free hydrothermal method. The nickel hydroxide nanoribbons were developed as electrocatalysts for urea electro-oxidation in alkaline media and showed more than 10 times enhancement in current density compared to bulk nickel hydroxide powders. The enhanced electrocatalytic oxidation of urea using nickel hydroxide nanoribbons reveals great potential for future applications in hydrogen production, remediation of urea-rich wastewater, and fuel cells.