Electrocatalytic oxidation of ethanol at copper bromide modified copper electrode in comparison to bare and copper chloride modified copper electrodes

Copper bromide modified copper electrode was prepared and used to electrocatalytic oxidation of ethanol. Scanning electron microscopy and energy dispersive x-ray experiments suggested the formation of thin layer of copper bromide on the copper surface. The j₀ for copper bromide modified copper and copper chloride modified copper electrodes are 9.8 and 5.7 folds respectively higher than for that of bare copper electrode. For copper bromide modified copper electrode, the charge transfer coefficient (α) and the number of electrons involved in the rate determining step (n_α) were calculated as 0.44 and 1 respectively.     

Zinc ion-imprinted polymer based on silica particles modified carbon paste electrodes for highly selective electrochemical determination of zinc ions

ABSTRACT

In this study, Zn(II) ion-imprinted polymer was prepared on the surface of vinyl silica particles and applied for detection of Zn(II) ions using differential pulse voltametry. The ion- imprinted polymer particles were prepared by free radical polymerization. The prepared particles were characterized by different morphological and elemental techniques. The ion-imprinted particles were used to fabricate the carbon paste electrode as a zinc ions sensor. The modified zinc sensor showed linear response in the concentration range 6.12 × 10^?9 to 4.59 × 10^?8 mol L^?1. The limit of detection and limit of quantification of the electrode were 1.351 × 10^?8 and 4.094 × 10^?8 mol L^?1, respectively.     

A diamino based resin modified silica composite for the selective recovery of tungsten from wastewater

A new adsorbent was developed by synthesizing 1,8‐diaminonaphthalene formaldehyde resin (DANFR) and coating it over the surface of silica gels. The silica composite was then treated with HCl for the activation of binding sites (?NH₃⁺Cl^?) on its surface. The structure of DANFR and its coating over the silanols were thoroughly characterized. Further, the adsorbent was applied to remove tungsten (W) from printed circuit board recycling unit wastewater that contained various co‐metal ions such as Na⁺, K⁺, Ca²⁺, Mg²⁺, Pb²⁺, NH₄⁺, Zn²⁺, Cu²⁺ and Mn²⁺. The selective removal was achieved due to the anion exchange mechanism of Cl^? with W(VI) while other cations get repelled from the surface (?NH₃⁺) of the DANFR‐silica composite. X‐ray photoelectron spectroscopy studies, Raman spectra and overlay chromatograms of ion chromatography demonstrated selective separation of WO₄^2? species from the wastewater. A removal capacity of 55.32 mg g^?1 for W(VI) was achieved from the wastewater within 45 min of reaction (pH ca 6.0). Simultaneous treatment with neat aqueous solution of W brings out 63.27 mg g^?1 of W(VI) removal. Finally, recovery of WO₄^2? ions and regeneration of the adsorbent were carried out by using alkaline solution which demonstrated successful desorption, as investigated by using ion chromatography. © 2016 Society of Chemical Industry     

Selective recovery of silver ions from aqueous solutions using modified silica beads with Adogen 364

In this work, a method to prepare new adsorbents for the recovery of silver ions was studied. Cheap silica beads for industrial use were obtained and silanized with dichlorodimethylsilane after pretreatment with hot water to increase the silanol contents, followed by immobilization of Adogen 364 (a mixture of trialkyl tertiary amines, Witco Co), a commercial solvent extractant that has a good affinity with silver ions. This sample, designated as K2WDA, was proven to be effective for the adsorption of silver ions from aqueous solutions with fast adsorption rates where sodium nitrate was added as a complexation agent to increase the adsorption capacity of the basic extractant. The adsorption capacity of K2WDA at pH 5 was 0.125 mmol g^?1 and corresponded to the proposed mechanism that silver ions adsorb on the functional group with a 1:1 molecular ratio. Selectivity for silver ions in synthetic plating wastewater containing Cu²⁺ and Ni²⁺ ions was excellent due to thermodynamic stability. In addition, 80% of the silver ions adsorbed could be recovered with sodium thiosulfate solution rather than acids and the solution was concentrated more than 10 times compared with the original solution. For practical application, a semi‐batch reactor was considered and numerical modeling was performed. © 2002 Society of Chemical Industry     

Diffusion study in a novel three-dimensional electrode for direct methanol fuel cells

A three-dimensional electrode formed by depositing Pt on polypyrrole treated polystyrene spheres (denoted as Pt/Ppy/PS) is prepared and characterized by different methods. The Pt/Ppy/PS prepared by using mixed polystyrene spheres of 200 nm-2 μm as support shows best performance for methanol oxidation due to the big and small holes or channels coexistent structure, which causes the difference in pressure inside the electrode and results in the reduction of the liquid sealing effect. The three-dimensional structure makes it easier for the liquid reactant to diffuse into the catalyst layer and the gaseous products evolve out from the catalyst layer. The diffusion behaviours of Pt/Ppy/PS and Pt/C electrodes are characterized by cyclic voltammetry. It is shown that the methanol oxidation on Pt/Ppy/PS electrode is not controlled by concentration polarization at slow scan rates, while the reaction on the traditional Pt/C electrode is diffusion controlled at all scan rates. The electrochemical impedance spectroscopic study (EIS) reveals that the three-dimensional electrode has higher active surface area.     

Studies of some operating parameters and cyclic voltammetry for a direct ethanol fuel cell

A direct ethanol fuel cell (DEFC) of 5 cm² membrane-electrode area was studied systematically by varying the catalyst loading, ethanol concentration, temperature and different Pt based electro-catalysts (Pt–Ru/C, Pt-black High Surface Area (HSA) and Pt/C). A combination of 2 M ethanol at the anode, pure oxygen at the cathode, 1 mg cm⁻² of Pt–Ru/C (40%:20%) as the anode and 1 mg cm⁻² of Pt-black as the cathode gave a maximum open circuit voltage (OCV) of 0.815 V, a short circuit current density of 27.90 mA cm⁻² and a power density of 10.3 mW cm⁻². The optimum temperatures of the anode and cathode were determined as 90 °C and 60 °C, respectively. The power density increased with increase in ethanol concentration and catalyst loading at the anode and cathode. However, the power density decreased slightly beyond 2 M ethanol concentration and 1 mg cm⁻² catalyst loading at the anode and cathode. These results were validated using cyclic voltammetry at single electrodes under similar conditions to those of the DEFC.     

A novel multienzyme electrode for the determination of citrate

A novel amperometric biosensor for the determination of citric acid in food samples and fermentation broths has been developed. The sensor is composed of citrate lyase (CL, EC 4.1.3.6), oxaloacetate decarboxylase (OAC, EC 4.1.1.3) and pyruvate oxidase (POP, EC 1.2.3.3), co-immobilized in gelatin, and an amperometric transducer. A Clark-type O₂-electrode and a modified Clark-type H₂O₂-electrode were alternatively used as a transducer. The biosensor covers a linear detection range from 1 μmol dm^?3 to 1 mmol dm^?3 citrate, with a response time of 2·5 min for the steady state response. The lower detection limit for citrate is 0·5 μmol dm^?3. The response of the sensor remained constant for 8 days and decreased to 25% after 18 days at 20–23°C. The results obtained from citrate determinations in food samples and fermentation broths agree well with those determined by enzymatic sample anlaysis. The relative standard deviation for citrate determinations with the new biosensor was 2·2% (n = 7).     

Copper chloride modified copper electrode: Application to electrocatalytic oxidation of methanol

Copper chloride modified copper (CCMC) electrode was prepared as a new electrode. For the preparation of the modified electrode, the polished copper electrode was placed in 0.1 M CuCl₂ solution for 20 s. In this step, a layer of copper (I) chloride was formed at the surface of copper electrode. Then, the electrode was placed in 0.1 M NaOH and the electrode potential was cycled between −250 and 1000 mV (vs. SCE) at a scan rate of 50 mV s⁻¹ for 5 cycles in a cyclic voltammetry regime until a featureless voltammogram was obtained. Surface physical characteristics of the modified electrode were studied by scanning electron micrographs (SEM). Results showed that considerable amounts of microcrystals have been formed on the copper surface during the modification. Surface elemental analysis of electrode were performed by energy dispersive X-ray (EDX) technique. The results showed that in addition to copper and chloride elements, there is also oxygen at the surface of CCMC electrode. This indicates that a layer of (ClCu)₂O was formed at the surface of the modified electrode. The electrocatalytic activity of the modified electrode for the oxidation of methanol, in aqueous basic solution was studied by using cyclic voltammetry. Results showed that, copper chloride modified electrode can improve the activity of Cu towards the oxidation of this small organic molecule, showing the possibility of attaining good electrocatalytic anodes for fuel cells. The modified electrode shows a stable and linear response in the concentration range of 5 × 10⁻³ to 8 × 10⁻² M with a correlation coefficient of 0.9958.     

Selective removal of copper ions from aqueous solutions using modified silica beads impregnated with LIX 84

Silica beads immobilized with 2‐hydroxy‐5‐nonylacetophenoneoxime (LIX 84) were prepared after silica surface modification by γ‐aminopropyltriethoxysilane (SB‐L). Batch and packed‐column tests were conducted to evaluate the metal ion removal capabilities of the prepared adsorbent. Equilibrium isotherms of the SB‐L with aqueous solutions containing copper ions were obtained. In addition, the kinetic performances for copper ion removal from aqueous solutions were investigated. The results showed that the amount of extraction increases with solution pH in the range between 1.5 and 5. The selectivity was also experimentally investigated, these results showed that the SB‐L adsorbed copper ions selectively in the presence of other metal ions such as Ni²⁺, Co²⁺, Zn²⁺, Cd²⁺, Ca²⁺ and Mg²⁺. From the regeneration experiments, it was found that the copper ions adsorbed at the SB‐L surface were recovered by acidic solutions. The recovery ratios were between 78% and 90%, depending on the types of acidic solutions. The results showed that the SB‐L prepared may be used for the selective extraction of copper ions from aqueous solutions. © 1999 Society of Chemical Industry     

Insight into the electroreduction of nitrate ions at a copper electrode, in neutral solution, after determination of their diffusion coefficient by electrochemical impedance spectroscopy

The electrochemical reduction of nitrate ions at a copper electrode in an unbuffered neutral aqueous solution is studied. Using a two compartment electrochemical cell, three stationary cathodic waves, noted P1, P2 and P3, were evidenced by cyclic voltammetry at −0.9, −1.2 and −1.3 V/SCE, respectively. By comparing the electrochemical response of nitrate and nitrite containing solutions, P1 was attributed to the reduction of nitrate to nitrite. In order to assign P2 and P3 features by determining the number of electrons involved at the corresponding potential, rotating disk electrode experiments at various rotation speeds, combined with linear sweep voltammetry, were performed. Current data analysis at a given potential was carried out using Koutecky-Levich treatment taking into account water reduction. Confident values of the diffusion coefficient D of nitrate ions were assessed by electrochemical impedance spectroscopy for nitrate concentrations of 10⁻³, 10⁻² and 10⁻¹ M. For a nitrate concentration of 10⁻² M, D was found to be 1.31 × 10⁻⁵ cm² s⁻¹ allowing the number of electrons to be determined as 6 for P2 and 8 for P3, in accordance with nitrate reduction into hydroxylamine and ammonia, respectively. The formation of hydroxylamine was confirmed by the observation of its reoxidation at a Pt microelectrode present at the Cu electrode/nitrate solution interface.     

Ameliorating effect of silica addition in the anode-catalyst layer of the membrane electrode assemblies for polymer electrolyte fuel cells

Incorporation of silica particles through a sol-gel process into the anode-catalyst layer with a sol-gel modified Nafion-silica composite membrane renders easy retention of back-diffused water from the cathode to anode through the composite membrane electrolyte, increases the catalyst-layer wettability and improves the performance of the Polymer Electrolyte Fuel Cell (PEFC) while operating under relative humidity (RH) values ranging between 18% and 100% with gaseous hydrogen and oxygen reactants at atmospheric pressure. A peak power density of 300 mW cm⁻² is achieved at a load current-density value of 1200 mA cm⁻² for the PEFC employing a sol-gel modified Nafion-silica composite membrane and operating at 18% RH. Under similar operating conditions, the PEFC with a Membrane Electrode Assembly (MEA) comprising Nafion-silica composite membrane with silica in the anode-catalyst layer delivers a peak power density of 375 mW cm⁻². By comparison, the PEFC employing commercial Nafion membrane fails to deliver satisfactory performance at 18% RH due to the limited availability of water at its anode, acerbated electro-osmotic drag of water from anode to cathode and insufficient water back diffusion from cathode to anode causing the MEA to dehydrate.     

Electrocatalytic oxidation of methanol and ethanol at carbon ceramic electrode modified with platinum nanoparticles

The use of carbon ceramic electrode (CCE) modified with platinum particles was studied for the electrocatalytic oxidation of methanol and ethanol by cyclic voltammetry and chronoamperometry. After preparation of a carbon ceramic as an electrode matrix by sol–gel technique, its surface was potentiostatically coated with Pt nanoparticles at −0.2 V vs. SCE in an aqueous solution of 0.1 M H₂SO₄ containing 0.002 M H₂PtCl₆. The electrocatalyst was characterized by XRD, SEM and cyclic voltammetry. The effective parameters on electrocatalytic oxidation of the alcohols, i.e. the amount Pt loadings, medium temperature and working potential limit in anodic direction were investigated and the results were discussed. This modified electrode showed an enhanced current density over the other Pt-modified electrodes making it more attractive for fuel cell applications.     

聚吡咯/活性炭复合电极对不同离子电吸附性研究

将小阴离子掺杂聚吡咯/活性炭(PPy/AC)复合电极与常规炭电极组装成非对称离子交换膜电容脱盐(MCDI)单元,研究了其对不同荷电量、水合半径离子的吸附性能差异。结果显示:当复合电极分别作为脱盐单元的正极或负极时,其电容吸附过程的离子尺寸依赖效应差异显著,这应该与复合电极氧化还原过程的孔径尺寸变化有关。     

Influence of electrode thickness on the performance of composite electrodes for SOFC

Measurements on half-cells consisting of yttria-stabilized zirconia (YSZ) electrolyte pellets and slurry-coated cathodes of different thickness were performed in order to determine the active area for oxygen reduction in composite cathodes of lanthanum strontium manganite (LSM) and YSZ. Electrochemical impedance spectroscopy was used to evaluate the main electrochemical parameters of the cathodic process. The temperature range was between 500 and 900 °C. The experimental results show a remarkable effect of the electrode thickness on the overall reaction rate in all the temperature range. At 750 °C a change in the controlling regime of the oxygen reduction is detectable and has been ascribed to the transition of the rate-determining step from a charge transfer to a mass transfer of the ionic species. A simplified theoretical model of the cathode that accounts for charge transfer and ionic conduction was developed to give insight into the experimental results. The model simulations compared satisfactorily with the experimental data confirming that the behaviour experimentally observed could be approached with the proposed model.     

聚苯胺/聚乙烯复合电极的制备及性能测定

以低密度聚乙烯（PE）为基体材料,乙烯-醋酸乙烯共聚物（EVA）为增韧剂,聚苯胺（PAn）和炭黑（CB）为导电添加剂制备复合电极板,探讨了原料配比对物理力学性能、电学性能的影响。结果表明,原料配比PE∶EVA∶CB=75%∶5%∶20%时,电极的电阻最小,但是其韧性不佳;当原料配比PE∶EVA∶（CB＋PAn）=85%∶5%∶10%时,复合电极板具有最好的韧性能。     

Heterogeneous synthesis of chelating resin organophosphonic acid‐functionalized silica gel and its adsorption property of heavy metal ions from fuel ethanol solutions

In this study, chelating resin silica gel chemically modified by poly(triethylenetetramine bis(methylenephosphonic acid)) (denoted as SG‐Cl‐T‐P) was successfully developed by heterogeneous synthesis method and used for adsorptive removal of heavy metal ions from fuel ethanol solutions, and the relevant modified organic group was calculated by DFT method at the B3LYP/6‐31 + G(d) level. SG‐Cl‐T‐P was characterized by Fourier transform infrared spectrometer, scanning electron microscope, energy dispersive X‐ray analysis system, porous analysis, etc. SG‐Cl‐T‐P has been used to investigate the adsorption of Hg(II),Cu(II), Mn(II), Co(II), Zn(II), Ni(II), Fe(III), and Cd(II) metal ions from ethanol solutions. The research results revealed that it has the better adsorption capacity for Hg(II) and Cd(II). © 2012 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

Electrocatalytic reduction of nitrate on copper electrode in alkaline solution

This work is devoted to the study of the kinetics and reaction mechanism of nitrate reduction on a copper electrode in 0.1 M NaOH, which acts as the supporting electrolyte. The experimental methods include cyclic voltammetry (CV), cronoamperometry (CA), controlled-potential electrolysis (CPE), and coulometry. In CV, there are three potential regions where charge transfer reactions take place, reactions which are associated with NO₃⁻ and/or intermediates reduction. Two isopotential points observed in CV indicate the existence of some competitive adsorption processes at the electrode surface.The three charge transfer steps were also made evident in the CA, CPE and coulometry studies. The correlation of the experimental results with the literature data led to the conclusion that NO₃⁻ reduction on a copper electrode in 0.1 M NaOH has an intermediate (N₂O₂²⁻) species, which reduces to N₂ at a potential of about −1.3 V and to NH₄OH at potential values lower than −1.4 V (both values are vs. SCE).     

Simultaneous detection of ascorbic acid, uric acid and homovanillic acid at copper modified electrode

The copper was deposited on glassy carbon (GC) and indium tin oxide (ITO) electrodes by electrochemical method. The copper structures on electrode were characterized by atomic force microscope, X-ray diffractometeric pattern and differential pulse voltammetric studies. Optimal conditions for uniform growth of copper structures on the electrode were established. Voltammetric sensor was fabricated using the copper deposited GC electrode for the simultaneous detection and determination of uric acid (UA) and homovanillic acid (HVA) in the presence of excess concentrations of ascorbic acid (AA). The voltammetric signals due to AA and UA oxidation were well separated with a potential difference of 400 mV and AA did not interfere with the measurement of UA and HVA at the GC/Cu electrode. Linear calibration curves were obtained in the concentration range 1-40 μM for AA and 20-50 μM for UA at physiological pH and a detection limit of 10 nM of UA in the presence of 10-fold excess concentrations of AA was achieved. The simultaneous detection of submicromolar concentrations of AA, UA and HVA was achieved at the GC/Cu electrode. The practical utility of the present GC/Cu modified electrode was demonstrated by measuring the AA content in Vitamin C tablet, UA content in human urine and blood serum samples with satisfactory results.     

燃料电池空气电极的孔道结构调控

燃料电池是将化学能转化成电能的装置,其空气电极催化层的设计,既要包含丰富的、易于接近的反应活性位,也要具备高度连通的电子、质子以及反应物、产物传质通道,因此电极必须具有特定三维几何结构形貌和有序分布的各功能化孔道,确保催化活性位得以充分利用以及反应可以连续进行。针对催化剂孔道的几何结构调控,本文调研了最近报道的一系列研究工作,从模板法、高温相变法、模板/相变复合方法以及基于金属有机框架材料进行孔道设计等四种主要方法出发,综述了该领域的最新研究进展。     

新型不锈钢基PbO2-WC-ZrO2复合电极材料的研制

在不锈钢基体上电沉积PbO2-WC-ZrO2复合镀层。研究了电沉积工艺参数对复合镀层的影响。确定了最佳工艺规范:J=3A/dm2,t=2.5h,θ=25°C,ρ(ZrO2)=40～50g/L,ρ(WC)=30～40g/L。获得了镀层结构均匀、致密,w(ZrO2)=4%～6%,w(WC)=7%～10%的PbO2-ZrO2-WC复合惰性阳极材料。将该阳极材料应用于电积锌其析氧电位为1700mV。新型PbO2-ZrO2-WC复合电极材料满足了惰性阳极材料的要求。