Selective oxidation of pentachlorophenol on diamond electrodes

The influence of electrode potential on pentachlorophenol (PCP) oxidation on boron doped diamond (BDD) electrodes in a 0.1 mol L^–1 Britton–Robinson buffer (pH 5.5) is described. Controlled potential electrolyses were carried at 0.9, 2.0 and 3.0 V vs Ag/AgCl and the solutions analysed by square wave voltammetry, high performance liquid chromatography, chloride ion selective electrode and spectroscopy in the ultraviolet–visible region. At low positive potential (0.9 V), the formation of an adherent film on the electrode surface involving the transference of 1 electron per PCP molecule was observed. The film was identified as the dimer 2,3,4,5,6-pentachloro-4-pentachlorophenoxy-2,5-cyclohexadienone and the current efficiency was as high as 90%. At potentials close to the onset of O₂ evolution (2.0 V), the formation of the corresponding quinone (p-tetrachlorobenzoquinone) was detected at the beginning of the process. This was followed by further oxidation to the hydroxy-benzoquinone with a practically quantitative yield. Electrolyses carried out well into the region of oxygen evolution (3.0 V) lead to the electrochemical combustion of PCP to CO₂ and H₂O as well as to the release into solution of 5 Cl^– ions per PCP molecule destroyed.     

Nanocomposites of manganese oxides and carbon nanotubes for aqueous supercapacitor stacks

Symmetrical supercapacitors and their serially connected two-cell stacks via a bipolar electrode were constructed with nanocomposites of manganese oxides and carbon nanotubes (MnO_x/CNTs) as the electrode materials. Nanocomposites with different contents of MnO_x were synthesised through the redox reaction between KMnO₄ and CNTs in aqueous solutions. The nanocomposites were characterised by scanning and transmission electron microscopy, BET nitrogen adsorption and X-ray diffraction before being examined in a three-electrode cell with a novel trenched graphite disc electrode by electrochemical means, including cyclic voltammetry, galvanostatic charging-discharging, and electrochemical impedance spectroscopy. The nanocomposites demonstrated capacitive behaviour in the potential range of 0-0.85 V (vs Ag/AgCl) in aqueous KCl electrolytes with less than 9% capacitance decrease after 9000 charging-discharging cycles. Symmetrical supercapacitors of identical positive and negative MnO_x/CNTs electrodes showed capacitive performance in good agreement with the individual electrodes (e.g. 0.90 V, 0.53 F, 1.3 cm²). The bipolarly connected two-cell stacks of the symmetrical cells exhibited characteristics in accordance with expectation, including a doubled stack voltage and reduced internal resistance per cell.     

水相和特殊介质中有序聚集体的结构、性质和应用(Ⅴ)——离子选择性电极在表面活性剂研究体系中的应用

综述了离子选择性电极在水体环境中检测表面活性剂的存在、在研究表面活性剂与生物大分子相互作用以及复配体系中表面活性剂胶束化行为与有序聚集体结构转变方面等领域的应用.同时介绍了上述领域应用的研究成果,并展望了表面活性剂离子选择性电极技术的发展趋势.     

Electro-oxidation of coal on NiO and/or Co3O4 modified TiO2/Pt electrodes

A TiO₂/Pt based electrode exhibited better activity for the oxidation of coal in a basic system compared to Ti/Pt, TiO₂–Cu/Pt and pure metal electrodes. The surface morphologies and composition of the electrodes were studied by SEM and XRD, respectively. Linear sweep voltammetry was employed to investigate the catalytic effects of electrodes, and the product of coal oxidization was determined by a gas collection test. The TiO₂/Pt electrodes that were modified with NiO and/or Co₃O₄ exhibited higher average currents and a lower decrease in mass during electrolysis compared to the other electrodes; this finding indicated that NiO and Co₃O₄ play important roles as catalysts.     

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.     

Electrocatalytic and simultaneous determination of isoproterenol, uric acid and folic acid at molybdenum (VI) complex-carbon nanotube paste electrode

This paper describes the development, electrochemical characterization and utilization of a novel modified molybdenum (VI) complex-carbon nanotube paste electrode for the electrocatalytic determination of isoproterenol (IP). The electrochemical profile of the proposed modified electrode was analyzed by cyclic voltammetry (CV) that showed a shift of the oxidation peak potential of IP at 175 mV to less positive value, compared with an unmodified carbon paste electrode. Differential pulse voltammetry (DPV) in 0.1 M phosphate buffer solution (PBS) at pH 7.0 was performed to determine IP in the range from 0.7 to 600.0 μM, with a detection limit of 35.0 nM. Then the modified electrode was used to determine IP in an excess of uric acid (UA) and folic acid (FA) by DPV. Finally, this method was used for the determination of IP in some real samples.     

Preparation and characterisation of poly(3,4-ethylenedioxythiophene) and poly(3,4-ethylenedioxythiophene)/poly(neutral red) modified carbon film electrodes, and application as sensors for hydrogen peroxide

Poly(3,4-ethylenedioxythiophene) (PEDOT) films have been prepared for the first time on carbon-film electrodes (CFE) in aqueous solution using electropolymerisation by potential cycling, potentiostatically and galavanostatically. Characterisation of the modified electrodes was done by cyclic voltammetry and electrochemical impedance spectroscopy and the stability of the polymer films was probed. The coated electrodes were tested for application as hydrogen peroxide sensors, by oxidation and reduction. A novel polymer film was also formed by modification of CFE by co-electropolymerisation of EDOT and the phenazine dye neutral red (NR) – (PEDOT/PNR) with a view to enhancing the properties for sensor applications. It was found that hydrogen peroxide reduction at the PEDOT/PNR coated electrodes could be carried out at a less negative potential, the sensor performance comparing very favourably with that of other polymer-modified electrodes reported in the literature.     

Impedance of blocking electrodes having parallel cylindrical pores with distributed radii

The impedance of blocking porous electrodes having parallel cylindrical pores with a lognormal distribution of their radii, identical pore depth and identical pore volume is calculated. Electrodes with size distribution of variable width, defined by different standard deviation (σ) values, are compared. The effect of varying σ is illustrated for the following cases: (i) the number of pores per unit surface (n) varies with σ while the median of the pore radius distribution (r_μ) remains constant; (ii) r_μ varies with σ while n remains constant; (iii) both n and r_μ vary with σ. It is shown that, although the general shape of the impedance plots is similar in all cases, the assumptions concerning n and r_μ have a major effect on the calculated frequency dependence. All impedance plots exhibit porous behaviour at high frequency and capacitive behaviour at low frequency, the transition being smoother for larger σ values. However, the frequency around which the porous-to-capacitive transition occurs depends on the additional assumptions: it increases as σ increases in cases (i) and (ii) but, in accordance with other authors’ calculations, decreases as σ increases for case (iii).     

Thiols deposition onto the surface of glassy carbon electrodes mediated by electrical potential

Electrochemical oxidation of thiols in acetonitrile and application of this process for modification of glassy carbon electrodes were studied. Addition of strong deprotonating agent, tetrabutylammonium hydroxide, was found to facilitate oxidation of thiols as well as their deposition onto the carbon surface. Thus, in the presence of 1 mM tetrabutylammonium hydroxide, glassy carbon electrode can be grafted with 1 mM 3-(nitrobenzyl)mercaptan at as low as +200 mV (vs. SCE). The modified electrodes were characterized by electrochemical methods and XPS confirming the stable binding of thiols which were absent on the surface of unmodified and control treated electrodes. Surprisingly, surface modification occurs independent of RS radicals formation and is explained by nucleophilic addition of deprotonated thiols to the surface of carbon electrode. The electrode potential plays an important role in this process presumably modulating electrophilic properties of the carbon surface.     

氢化物电极放电动力学的研究

探讨了氢化物电极放电的动力学过程,建立了电极放电容量与放电电流、电极材料颗粒尺寸等因素的理论关系式,分析了各因素对放电容量的影响.实验结果与理论关系吻合良好.