Multilayer Assemblies Consisting of Tri‐Vanadium‐Substituted Heteropolyanions and Its Electrocatalytic Properties

We describe the controlled fabrication of ultrathin multilayer films consisting of tri‐vanadium‐ substituted heteropolytungstate anions (denoted as P₂W₁₅V₃) and a cationic polymer of quaternized poly (4‐vinylpyridine) partially complexed with osmium bis(2,2′‐bipyridine) (denoted as QPVP‐Os) on the 4‐aminobenzoic acid (4‐ABA) modified glassy carbon electrode (GCE) surface based on layer‐by‐layer assembly. Cyclic voltammetry and UV‐vis absorption spectrometry have been used to easily monitor the thickness and uniformity of thus‐formed multilayer films. The V‐centered redox reaction of P₂W₁₅V₃ in the multilayer films can effectively catalyze the reduction of BrO and NO . The resulting P₂W₁₅V₃/QPVP‐Os multilayer film modified electrode behaves as a much promising electrochemical sensor because of the low overpotential for the catalytic reduction of BrO and NO , and the catalytic oxidation of ascorbic acid.     

聚合电流对锂/聚吡咯电池正极电化学行为的影响

在Pt微盘电极上用恒电流技术在电流密度为0.05-10 mA·cm-2范围合成了1 滋m厚度的聚吡咯(PPy)膜. 采用循环伏安(CV)、计时电势、交流阻抗(EIS)技术考察了不同聚合电流下得到的聚吡咯的电化学行为. 结果表明, 最佳聚合电流区间为1-5 mA·cm-2, 对应的电势一般在3.9-4.1V (vs Li/Li+)之间, PPy的掺杂度为30%左右. 在这一聚合电流密度范围得到的PPy具有较大的电化学容量, 较佳的电化学反应可逆性能、较高的氧化还原电势数值和稳定性能. 处于氧化态的聚吡咯具有优良的导电性. 上述条件下得到的PPy适合于作为锂离子二次电池的正极材料. 适当选择电流, 可以得到有相对完整的共轭仔键的长链结构的PPy 膜.     

Electrochemistry of monoazahemin reconstituted myoglobin at an indium oxide electrode

Monoazahemin reconstituted myoglobin was prepared and its electrochemical behavior was studied in comparison with native myoglobin. For both myoglobins well-defined voltammograms were clearly obtained at highly hydrophilic surfaces of indium oxide electrodes. Although monoazahemin showed a more positive redox potential than hemin (measured in methanol), monoazahemin reconstituted myoglobin showed a more negative redox potential than native myoglobin in a 50 mM bis-Tris buffer solution (pH 6.5), suggesting that for both native and reconstituted myoglobins the heme environment including proximal histidine as an axial ligand of the redox center plays an important role in determining the redox potential. Also, a unique electrochemical response of cyano-monoazahemin reconstituted myoglobin was demonstrated.     

Investigation of Electrochemical Behavior of Some Dithiophosphonates in Acetonitrile on the Platinum and Gold Electrodes

Some dithiophosphonate derivatives were synthesized and the electrochemical reduction mechanism was investigated by cyclic voltammetry (CV), square wave voltammetry (SWV) and chronoamperometry (CA) in 0.1 M tetrabutylammoniumtetrafluoroborate (TBATFB) in acetonitrile at platinum (Pt) and gold (Au) electrodes. Dithiophosphonates showed a cyclic voltammetric reduction peak at about ?1.1 V at Pt and ?1.3 V at Au electrode (vs. Ag/Ag⁺) in this media. It was also shown that dithiophosphonates can be determined quantitatively in acetonitrile using a calibration graph. The number of electrons transferred were calculated as 2 using ferrocene as a reference compound at the UME electrode. Mechanism of dithiophosphonates was also examined on Pt and Au electrodes and electrochemical reduction of dithiophosphonates seems to follow an EC mechanism with an irreversible electron transfer step. The reaction product in the bulk electrolysis experiment was isolated and identified using proton‐coupled P‐31 NMR, ¹³C‐NMR and IR spectroscopy. The adsorption tests for dithiophosphonates were revealed that no strong or weak adsorption phenomena exist on both Pt and Au electrodes. Simulation curves were acquired by DigiSim 3.03 version to investigate the reduction mechanism and to estimate the kinetic parameters for electrochemical and chemical steps.     

Influence of the specific adsorption of anions on the “double layer region” of the cyclic voltammetric curves obtained with platinized platinum electrodes

Cyclic voltammetric study of platinized electrodes restricted to the potential range corresponding to the “double-layer region” (350–700 mV on RHE scale) was carried out in acid medium in the presence of, HSO⁻ ₄, H₂PO⁻ ₄, Cl⁻ and ClO⁻ ₄ anions. It is shown that the shape of the voltammetric curves strongly depends on the nature of the anions present in the system. The phenomena observed are ascribed to the specific adsorption of anions. A correlation is found between the results of radiotracer adsorption studies (differential voltradiometric curves) and the voltammetric measurements. Received: 24 September 1997 / Accepted: 25 November 1997     

Electrochemical and Raman spectroscopic study of polyaniline; influence of the potential on the degradation of polyaniline

The polymerization of aniline has been studied employing in-situ electrochemical and Raman spectroscopical techniques. Aniline was polymerized by cyclic voltammetry on a Pt surface in sulfuric acid solutions of aniline. The Raman bands were assigned for degradation products of the overoxidized form of polyaniline. A discussion of the degradation mechanism is given. Received: 12 November 1997 / Accepted: 20 January 1998     

Electrochromic properties of sputtered TiO2 thin films

TiO₂ thin films were deposited on ITO/Glass substrates by the rf magnetron sputtering in this study. The electrochromic properties of TiO₂ films were investigated using cyclic voltammograms (CV), which were carried out on TiO₂ films immersed in an electrolyte of 1 M LiClO₄ in propylene carbonate (PC). As- deposited TiO₂ thin film was amorphous, while the films post-annealed at 300~600°C contained crystallized anatase and rutile. With the increase of the annealing temperature, the surface roughness of film increased from 1.232 nm to 1.950 nm. Experimental results reveal that the processing parameters of TiO₂ thin films will influence the electrochromic properties such as transmittance, ion-storage capacity, inserted charge, optical density change, coloration efficiency and insertion coefficient.     

Exploration of electrodeposited platinum alloy catalysts for methanol electro-oxidation in 0.5 M H<Subscript>2</Subscript>SO<Subscript>4</Subscript>: Pt-Ni system

In this work, we examine the electrocatalytic activity of electrodeposited Platinum (Pt)-Nickel (Ni) alloy layers on an inert substrate electrode for methanol oxidation reaction. Analyses using energy-dispersive fluorescent X-ray analysis and powder X-ray diffractometry confirm alloying of Pt with Ni in a range of compositions. Steady-state polarisation measurements in 0.5 M methanol+0.5 M H₂SO₄ solutions clearly show that the onset of electro-oxidation shifts to less anodic potential values (approximately 160 mV), while also exhibiting current enhancements up to ~15 times the currents obtained for the pure Pt electrodeposit. A linear relationship between the cyclic voltammetric peak (oxidation) current and [MeOH] is observed at a scan rate of 50 mVs^–1, thus indicating reduced influence of adsorbed CO (CO_ads) surface poison. A critical composition, Pt (92%)/Ni (8%) [denoted Pt-Ni(3) alloy] is found to exhibit maximum electrocatalytic activity, beyond which the activity drops, whereas pure Ni does not catalyse the reaction. While the promotion of electro-oxidation is understood to be largely due to the alloy catalyst, surface redox species of Ni oxide formed during the electro-oxidation process may also contribute to the oxygenation of CO_ads, thereby enhancing the oxidation current. Plausible mechanisms of methanol oxidation on Pt/ transition metal alloy electrocatalysts are discussed in terms of electron transfer (in the alloy) and the role of Ni oxide species.     

Determination of extremely low percolation threshold electroactivity of the blend polyvinyl chloride/polyaniline doped with camphorsulfonic acid by cyclic voltammetry method

The percolation threshold of prepared blends of poly(vinyl chloride) (PVC) with doped polyaniline (PANi) from camphorsulfonic acid (CSA) was investigated by cyclic voltammetry. The blends were formed from N-methyl pyrrolidone (NMP) solutions and PANi-CSA/PVC with weight fractions from 0.1% to 0.005%. The film of blends were prepared by casting the above polymer solutions on a glass carbon (GC) electrode. Voltammograms were drew in a one-compartment cell fitted with a GC electrode, Pt electrode and SCE as working, auxiliary and reference electrode respectively, in 1 M perchloric acid as electrolytic solution. The obtained results showed that PANi-CSA/PVC blend onto 0.007% weight from PANi is electroactive. The structure and morphology of prepared blends were investigated by FT-IR spectra and optic microscope.     

液/液界面新溶剂体系的电化学研究

用循环伏安法测定了离子在水-异硫氰酸烯丙脂(AIT)体系中的标准转移Gibbs能△_o~w G_(tr,i)~0。对含有AIT的混合溶剂的研究, 发现了一系列电位窗比较宽的水/有机溶剂体系, 讨论了溶剂效应对△_o~w G_(tr,i)~0的影响。