Electrode reactions of nitroxide radicals at platinum in acetonitrile

Electrode reactions of 2,2,6,6-tetramethylpiperidinenitroxide (TMPNO) and di-tert-butylnitroxide (DTBNO) at platinum in acetonitrile solution were investigated by means of linear sweep voltammetry and controlled potential coulometry. In the case of TMPNO, the voltammetric resuls were satisfied with diagnostic criteria for reversible charge transfer, and those of esr and coulometry led to one electron transfer. In the case of DTBNO, the coulometric results in which apparent number of electron was $\text{1}\text{3}$ times the real one led to a mechanism with interesting series of reactions. This was also confirmed by esr.     

Electro-oxidation of N-hydroxy imides for redox mediator in acetonitrile containing lutidine as a base

The electrochemical properties of two N-hydroxy imides, N-hydroxymaleimide and N-hydroxysuccinimide, at a glassy carbon electrode in acetonitrile were examined by cyclic voltammetry. N-hydroxysuccinimide, which contains no olefinic linkage, indicated a chemically reversible redox response, and its ability as a mediator for the oxidation of benzyl alcohol was confirmed by rotating disk electrode voltammetry.     

铋膜电极测定辣椒制品中苏丹红Ⅱ的研究

用循环伏安法(CV)、线性扫描伏安法(LSV)研究了苏丹红Ⅱ在铋膜电极上的电化学行为。结果表明,在最佳条件下,BR缓冲溶液(pH=2),无水乙醇作助溶剂(体积分数27.5%),苏丹红Ⅱ在-0.50附近有一灵敏还原吸收峰。用线性扫描伏安法测定标准品,扫描速度为100 mV/s,浓度在7.49×10-6~1.87×10-5范围内和峰高呈线性关系。回归线方程:pí=1.722 2+0.751 7c(×10-3mmol/L),r=0.994 8。检出限为3.74×10-4mmol/L。据此建立了一种快速、简便测定苏丹红Ⅱ的方法。     

Electrochemical determination of bisphenol A at Mg-Al-CO3 layered double hydroxide modified glassy carbon electrode

The electrochemical behavior of bisphenol A (BPA) was investigated on Mg-Al layered double hydroxide (LDH) modified glassy carbon electrode (GCE) by cyclic voltammetry (CV), differential pulse voltammetry (DPV), linear sweep voltammetry (LSV) and chronocoulometry (CC). The cyclic voltammogram of BPA on the modified electrode exhibited a well defined anodic peak at 0.454 V in 0.1 M pH 8.0 phosphate buffer solution (PBS). The experimental parameters were optimized and the kinetic parameters were investigated. The probable oxidation mechanism was proposed. Under the optimized conditions, the oxidation peak current was proportional to BPA concentration in the range from 1 × 10⁻⁸ to 1.05 × 10⁻⁶ M with the correlation coefficient of 0.9959. The detection limit was 5.0 × 10⁻⁹ M (S/N = 3). The fabricated electrode showed good reproducibility, stability and anti-interference. The proposed method was successfully applied to determine BPA in plastic products and the results were satisfactory.     

金电极线性扫描溶出伏安法测定菠菜中的重金属Pb

采用金电极线性扫描溶出伏安法对菠菜中的重金属Pb进行测定,结果显示对Pb(Ⅱ)测定具有较高准确度,检出限为1.5×10-6g·L-1,回收率在97.4%~102.6%,RSD为2.36%。该法仪器简单、操作简便,测定Pb的灵敏度可达到原子吸收法水平,通过改善工作电极富集能力,进一步提高灵敏度,即可实现多种元素的连续快速测定。     

Theory of linear sweep/cyclic voltammetry for the electrochemical reaction mechanism involving a redox catalyst couple attached to a spherical electrode

The catalytic mechanism O_ad + ne⁻ ? R_ad, , involving a redox couple (O_ad, R_ad) attached to the electrode, and soluble species (C_sol, D_sol), is a precursor for many contemporary electrocatalytic reaction models. The theory of cyclic voltammetry for this mechanism was presented long ago for planar electrodes. Analogous rigorous theory for spherical electrodes has not been available thus far, despite the fact that the use of spherical microelectrodes for kinetic studies is often advantageous. By adopting the integral equation formalism, combined with the recently developed adaptive Huber method for integral equations, we obtain such a rigorous theory. The theory is applicable for any value of the electrode radius r₀, from planar electrodes (r₀ → ∞), to ultramicroelectrodes (r₀ → 0). With the decreasing electrode radii the current functions increase, gradually approaching steady-state sigmoidal waves. Equations for the dependences of the forward peak potentials on dimensionless model parameters, and equations for steady-state voltammograms, obtained in this work, can be used for model verification and parameter estimation.     

The role of platinum oxide in the electrode system Pt(O2)/yttria-stabilized zirconia

The existence and role of platinum oxide in the solid state electrode system Pt(O₂)/yttria-stabilized zirconia is discussed. Covering and porous model-type Pt film electrodes on YSZ single crystals are investigated by cyclic voltammetry, electrochemical impedance spectroscopy, and in situ scanning photoelectron microscopy. The formation of Pt oxide and its amount strongly depend on the experimental conditions, such as temperature, oxygen partial pressure, and oxygen flux towards the electrode during anodic polarization. Electrode activation and deactivation processes can be explained by formation and decomposition of Pt oxide, which is reducing or inhibiting the oxygen exchange rate.     

螺旋霉素的水／硝基苯界面循环伏安法研究及其测定

本文利用循环伏安法研究了螺旋霉素推动质子从水相向硝基苯相转移的过程，并建立了一种新的测定螺旋霉素有效含量的电化学方法     

Synthesis and electrochemical properties of redox active polyurethanes with ferrocene units in polyether soft segments

Electrochemical active segmented polyurethane with ferrocene units in polyether soft segments (PU‐S‐Fc) has been originally synthesized and identified by ¹H‐NMR spectra. Electrochemical behaviors of PU‐S‐Fc blending with lithium perchlorates were investigated by cyclic voltammetry. In N,N′‐dimethyl formide solution, PU‐S‐Fc exhibited normal cathodic and anodic peaks of the ferrocene/ferricinium (Fc/Fc⁺) couple. Compared with that of ferrocene molecules blended in ordinary polyurethane (PU‐B‐Fc), redox peaks of ferrocene units in PU‐S‐Fc were found to be broader, which may be ascribed to the weak adsorption of the polyurethane on the electrode surface. The influence of lithium perchlorate concentration on peak potentials indicated that supporting electrolytes played an important role in electrochemical redox of PU‐S‐Fc. In the solid state, PU‐S‐Fc/Li⁺ showed discernible redox peaks at temperatures higher than 60°C, and an exponential increase curve of electrochemical response with an increase of temperature was found. Temperature variations of the solid‐state ionic conductivity for PU‐S‐Fc/Li⁺ can be interpreted by the Arrhenius equation. The similarity between the temperature dependence of ionic conductivity and electrochemical response revealed that transport mechanism of ionic and redox species in the polyurethane matrix was controlled by the mobility of polyether chains. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 74: 2674–2680, 1999     

Isothermal emulsion polymerization of n‐butyl methacrylate with KPS and redox initiators: Kinetic study at different surfactant/initiator concentrations and reaction temperature

Thermal initiators, although widely used in emulsion polymerization, are limited to high reaction temperatures due to their high activation energy. Redox initiators have low activation energies indicating that emulsion polymerization could be conducted at lower temperatures to save energy. In the present study, a redox initiator system comprised of hydrogen peroxide (H₂O₂) and ascorbic acid (AA) in conjunction with a Fe²⁺ ion catalyst is compared with a potassium persulfate (KPS) thermal initiator in an emulsion polymerization system consisting of n‐butyl methacrylate (BMA), sodium lauryl sulfate (SLS) and water. The dependence of particle number on surfactant and initiator concentrations shows that redox‐ and KPS‐initiated systems both follow the Smith‐Ewart theory. However, the high radical flux generated from the redox initiator results in the formation of much smaller latex particles and higher reaction rate with lower molecular weights. Latex particle size and molecular weight could also be influenced by reaction temperature. By using redox initiator, small monodisperse particles (diameter < 50 nm) can be achieved without using a large amount of surfactant. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 43037.     

Influence of ionic speciation on electrocatalytic performance of polyaniline coated platinum electrode: Fe(III)/Fe(II) redox reaction

Porous-polyaniline coated Pt electrode (PANI/Pt) was electro-synthesized potentiodynamically in 0.1 M aniline + 0.5 M H₂SO₄ and morphologically characterized by scanning electron microscopy (SEM). Nature of predominant Fe-species in HCl and H₂SO₄ was checked by UV-vis spectrophotometry. Electrocatalysis of Fe(III)/Fe(II) reaction was studied by cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS) for three different solution compositions viz. (i) FeCl₃/FeCl₂ in 1 M HCl, (ii) FeCl₃/FeCl₂ in 0.5 M H₂SO₄ and (iii) Fe₂(SO₄)₃/FeSO₄ in 0.5 M H₂SO₄. For different thicknesses of PANI, the peak current increased irrespective of the nature of the Fe-species, but the polarity of the charge on the Fe-species showed great influence on reversibility of electrocatalysis by PANI/Pt. The Donnan interaction of the polyaniline modified electrode for the three compositions was investigated with respect to [Fe(CN)₆]³⁻/H₂[Fe(CN)₆]²⁻ which are believed to be the predominant species present in K₃[Fe(CN)₆]/K₄[Fe(CN)₆] solution in 0.5 M H₂SO₄. The electrocatalytic performance of PANI/Pt for Fe(III)/Fe(II) redox reaction was found superior in HCl compared to that in H₂SO₄.     

Electrocatalytic oxidation of methanol to soluble products on polycrystalline platinum: Application of convolution potential sweep voltammetry in the estimation of kinetic parameters

Irreversible oxidation of methanol on polycrystalline platinum leading to soluble products has been carried out by fast scan voltammetry, and the reaction has been studied under diffusion controlled process. The conventional analysis of current–potential data, viz. dependence of peak potential on scan rate and peak width measurements, resulted in the estimation of apparent diffusion coefficient of methanol and the anodic transfer coefficient of the electrode reaction. However, from the convolution potential sweep voltammetry, a more accurate and reliable kinetic data were obtained. Under the above conditions, methanol oxidation follows Butler–Volmer rate law with a linear variation of logarithmic heterogeneous rate constant with electrode potential. A constant apparent anodic transfer coefficient independent of electrode potential was observed pointing to the fact that the standard potential of the reaction cannot be determined from the voltammetric experiments. The experimental current–potential curve was compared with a theoretical voltammogram and further oxidation of products at the electrode surface has also been analyzed using limiting convolution current.     

Cyclic voltammetric behaviour and some surface characteristics of the lead electrode in aqueous HCL solutions

The positive linear sweep voltammograms of lead were investigated in 0.01–2.00 M aqueous HCl solutions. The results revealed the occurrence of one anodic current peak as the result of formation of a thin PbCl₂ surface layer. Intensive study of the electrochemical behaviour of the lead electrode in 1.00 M HCl solution was carried out by cyclic voltammetry. The results indicated that the formation of PbCl₂ is a reversible process controlled by diffusion of Cl^? ions to the electrode surface. Controlling the voltammetric conditions enabled the building up of a relatively thick and porous PbCl₂ layer that could resist rupture or breakdown. In addition, the electrode surface products were examined by scanning electron microscopy and X-ray diffractometry. The morphology of the as-formed PbCl₂ layers showed a primitive dependence on the voltammetric conditions. X-ray diffraction analysis proved that only PbCl₂ was formed on the electrode surface and no other products could be detected.     

Electrocatalytic reduction of oxygen at glassy carbon electrode modified by polypyrrole/anthraquinones composite film in various pH media

The electrocatalytic reduction of dioxygen by one mono and four dihydroxy derivatives of 9,10-anthraquinone (AQ) incorporated in polypyrrole (PPy) matrix on glassy carbon electrode has been investigated. The electrochemical behaviour of the modified electrodes was examined in various pH media and both the formal potential of anthraquinones and reduction potential of dioxygen exhibited pH dependence. AQ and PPy composite film showed excellent electrocatalytic performance for the reduction of O₂ to H₂O₂. pH 6.0 was chosen as the most suitable medium to study the electrocatalysis by comparing the peak potential of oxygen reduction and enhancement in peak current for oxygen reduction. The diffusion coefficient values of AQ at the modified electrodes and the number of electrons involved in AQ reduction were evaluated by chronoamperometric and chronocoulometric techniques, respectively. In addition, hydrodynamic voltammetric studies showed the involvement of two electrons in O₂ reduction. The mass specific activity of AQ used, the diffusion coefficient of oxygen and the heterogeneous rate constants for the oxygen reduction at the surface of modified electrodes were also determined by rotating disk voltammetry.     

Transient microkinetic modelling of n-heptane catalytic cracking over H-USY zeolite

A microkinetic model for the catalytic cracking of n-heptane is proposed comprising a set of significant elementary steps which generate a complex reaction network. This approach constitutes a compromise between fundamental and lumped models since the reaction scheme is detailed to the carbon atom level by considering separately olefins, paraffins and adsorbed carbenium ions with the same carbon atom number. Elementary rate constants are estimated through expressions relating species reactivity with their carbon atom number. Fitting the model against experimental data over a large parameter space was performed using a micro-genetic algorithm with binary encoding and logarithmic distribution. The advantage of this approach is that it allows modelling the reaction network without supposition of rate determining steps. The model predicts very well the observed transient activity for n-heptane cracking over H-USY zeolite at and in general, it reasonably predicts the experimental trends for the products distribution.     

Electrode reaction of the Np3+/Np couple at liquid Cd and Bi electrodes in LiCl–KCl eutectic melts

The electrode reactions of the Np³⁺/Np couple at liquid Cd and Bi electrodes were investigated by cyclic voltammetry at 723, 773 and 823 K in the LiCl–KCl eutectic melt. It was found that the diffusion of Np³⁺ in the salt phase was the rate-determining step in the cathodic reaction when the concentration of NpCl₃ was less than about 1 wt % and the liquid Cd or Bi phase was not saturated with Np. The redox potentials of the Np³⁺/Np couple at the liquid Cd electrode at 723, 773 and 823 K were observed to be more positive than those at the Mo electrode by 0.158, 0.140 and 0.126 V, respectively. The potential shift results from a lowering of the activity of Np in the Cd phase according to the formation of the NpCd₁₁ alloy at 723 K and NpCd₆ at 773 and 823 K. The redox potentials of the Np³⁺/Np couple at the liquid Bi electrode at 723, 773 and 823 K were more positive than those at the Mo electrode by 0.427, 0.419 and 0.410 V, respectively, which is attributable to a lowering of the activity of Np in the Bi phase due to the formation of NpBi₂.     

Time resolved impedance spectroscopy as a probe of electrochemical kinetics: The ferro/ferricyanide redox reaction in the presence of anion adsorption on thin film gold

In this work, we use the time resolved technique of Fourier transform electrochemical impedance spectroscopy (FT-EIS) for quantitative kinetic analyses of Faradaic and nonfardaic, as well as heterogeneous and adsorption reactions. As a model system, we investigate the Fe(CN)₆^3−/4− redox reaction on a thin film Au electrode in the presence of nonfaradaically adsorbing ClO₄⁻ or Cl⁻ in neutral electrolytes. The redox process indicates a predominantly Faradaic outer sphere reaction, with nearly negligible adsorption of reactants on Au. dc voltage dependent kinetic parameters for both the anion and redox reactions are obtained by FT-EIS in real time during cyclic voltammetry. Equilibrium values of reaction rate constants, adsorption resistances and pseudocapacitances for the redox couple are also obtained. The theoretical background and working principles of these measurements are discussed, and the experimental findings are compared with previously published data.     

In situ Raman spectroelectrochemical study of redox processes at poly(Toluidine blue) modified electrode

Electrooxidation of hydroquinone and ascorbic acid at a gold electrode modified with electropolymerized layer of phenothiazine dye Toluidine blue (PTB) has been studied with the use of in situ Raman spectroelectrochemical technique, surface enhanced resonance Raman spectroscopy (SERRS). It was shown that the redox state of PTB at any electrode potential can be determined in pH 1.0 and 4.0 solutions following specific changes in Raman spectra of these modifier layers. Electrooxidation of hydroquinone at PTB modified electrode in pH 1.0 solution, and of ascorbic acid in pH 4.0 solution, proceed without any detectable changes in a net redox state of modifier layers. It has been concluded that, under the conditions studied, both anodic oxidation processes occur most probably at the modifier/electrolyte interface rather than within the modifier film, as opposed to electrooxidation of same species at polyaniline modified electrodes studied earlier.     

金属钴卟啉负载炭黑在碱性介质中的性质研究

将合成的四甲氧基苯基钴卟啉(CoTMPP)负载于经过双氧水和硝酸预处理且掺杂了MnOx的炭载体上,作为氧还原电催化剂。采用X射线衍射(XRD)、红外透射光谱(IR)、循环伏安曲线(CV)和Koutevky-Levich关系式评价了电催化剂对氧还原反应的电催化性能。结果表明,在碱性介质中,MnOx的掺杂有利于提高催化剂的催化活性,CoTMPP负载于6 mol/L硝酸处理过的炭载体BP 2000上活性较好,同时发现焙烧的最佳温度是900℃。     

Amperometric glucose biosensor based on immobilization of glucose oxidase in electropolymerized o-aminophenol film at Prussian blue-modified platinum electrode

An amperometric glucose biosensor is developed, based on immobilization of glucose oxidase (GO_X) in an electrochemically polymerized, non-conducting poly(o-aminophenol) (POAP) film at Prussian blue (PB)-modified platinum (Pt) microelectrode. Effects of polymerization cycle number for POAP and PB, applied potential used in the determination, pH value of the detection solution and electroactive compounds on the amperometric response of the sensor were investigated and discussed. The electroactive property and rough surface of PB film result in the improvement of the detection limit and the increase of the maximum response current and sensitivity. The biosensor based on Pt/PB/POAP/GO_X electrode has two times lower detection limit, five times larger maximum current and nine times higher sensitivity than those of the biosensor based on Pt/POAP/GO_X electrode. Additionally, the biosensor shows fast response time, large response current, and good anti-interferent ability for l-ascorbic acid, uric acid and acetaminophen. Excellent reproducibility and stability of biosensor are also observed.