Electrochemical synthesis of polypyrrole films over each of well-aligned carbon nanotubes

Polypyrrole (PPy) films were uniformly electropolymerized over each carbon nanotube of the well-aligned carbon nanotube arrays. For comparison, PPy films were also coated on flat metallic titanium (Ti) and platinum (Pt) substrates by the same technique. The synthesis and the redox performance of the PPy films were conducted by cyclic voltammetry (CV). The structural characterization including the thickness and uniformity of the PPy films was carried out by scanning electron microscopy (SEM) and transmission electron microscopy (TEM). It is observed that the coating of the PPy film over carbon nanotubes is much faster than that on flat Ti/Pt surface. Furthermore, the redox performance of the PPy-coated carbon nanotube electrodes over flat Ti/Pt electrodes was significantly improved due to the high accessible surface area of the carbon nanotubes in the aligned arrays, especially in large film formation charge (Q_film). It is very promising that the electrode developed in this study could be used as high performance electrode in rechargeable batteries.     

Electrochemical synthesis of polypyrrole films on copper from phytic solution for corrosion protection

Phytic acid (C₆H₁₈O₂₄P₆), the principal phosphorous storage form in many plant tissues, is a green material. A polypyrrole (PPy) doped with phytic acid (IP₆) was electrosynthesised on copper from an aqueous phytic acid solution. Raman spectroscopy, X-ray photoelectron spectroscopy (XPS) and SEM were used to characterise the polymer. The polymer-covered copper was subjected to a corrosion test in NaCl solution. The dissolution of copper covered with PPy-IP₆ was found to be greatly inhibited in NaCl solution. The inhibition indicated protection of the PPy-IP₆ layer against copper corrosion.     

砷黄铁矿在酸性体系下的电化学氧化

在酸性体系下研究砷黄铁矿的电化学氧化。结果表明:砷黄铁矿首先被氧化为As2S2,覆盖于电极表面,使电极表面发生钝化;随着电位的继续升高,As2S2被氧化生成亚砷酸,随后亚砷酸被氧化为砷酸,亚铁离子被氧化成铁离子。不同pH和温度下的腐蚀动力学研究表明,随着pH值的增大,体系的腐蚀电位正移,腐蚀电流密度减小;随着温度的升高,砷黄铁矿的腐蚀电位负移,腐蚀电流密度增大。说明在研究的pH及温度范围内,降低体系的pH或提高温度都有利于砷黄铁矿的氧化。交流阻抗研究结果表明,不同电位下电极表面发生的电化学反应机理不同,测定结果与线性扫描的研究结果相吻合。     

Electrochemical synthesis of polypyrrole nanowires on composite electrode

Polypyrrole nanowires growing with two-dimensional instantaneous nucleation and one-dimensional growth pattern were realized on graphite/paraffin composite electrode in phosphate buffer solution.     

Electrochemical synthesis of polypyrrole macro-tubes on aluminum substrate

A novel structure of conductive polymer films was synthesized by electropolymerization on aluminum substrate under potentiostatic condition at a relatively high applied potential. A thick film of polypyrrole was electrodeposited onto aluminum substrate from an aqueous electrolyte solution of NaNO₃ with pH 12 by applying a constant potential of 2.0 V versus SCE. This polypyrrole film has a good stability with strong adhesion to the substrate surface. However, the morphological structure of the film is different from those previously observed for conductive polymers. Large tubes (ca. 100–200 μm in diameter) are formed, which are spiraled around the cylindrical substrate electrode. Although, the internal channels of these polypyrrole macro-tubes are very wide, the polypyrrole synthesized is sufficiently dense, guaranteeing excellent mechanical stability for this novel morphological structure. On the other hand, such large walls of the macro-tubes have nano-structures.     

Electrochemical behavior of aluminium in acidic media

The inhibitive action of the acid extracts of seeds' leaves and bark from the Ficus virens plant towards hydrochloric and sulfuric acid corrosion of aluminium is tested using mass loss and thermometric techniques. It was found that the extract acts as a good corrosion inhibitor for aluminium corrosion in all concentration of hydrochloric and sulfuric acid solution. The ellagic acid has been used as a representative of the tannin species. The tannins are anodic inhibitors. The inhibition efficiency (IE) increases as the extract concentration is increased. The effect of temperature on the IE was studied. It was found that the presence of extract increases the activation energy of the corrosion reaction. Moreover, the heat of adsorption (Q_ads) was also calculated. It was found that the Ficus virens extract provides a good protection against pitting corrosion in chloride ion containing solution.     

Electrochemical properties of the polypyrrole films doped with benzenesulfonate

The electrochemical redox behavior of the polypyrrole films doped with benzenesulfonate was investigated by cyclic voltammetry, the surface morphology of the films was characterized by AFM, and the interactions between pyrrole oligomers and the benzenesulfonate anion were modeled with quantum chemical methods. It is the first systematic study of the redox properties of this interesting system, somewhat of a model system with two complementing interactions (electrostatic and aromatic stacking). The influence of the electrodeposition charge and current density on the properties of the polymer film is explored. The voltammetric measurements show that redoxactivity of the polypyrrole films doped with benzenesulfonate anions is quite high, and markedly depends on the thickness of the film. Experiments with bilayered films show that electrode surface has an important but limited impact on the formation of organized compact structures.     

Electrochemical properties of iron silicocarbide and cementite in acidic and neutral environments

Voluminous specimens of individual Fe₅SiC iron silicocarbide and Fe₃C iron carbide phases were produced by mechanical alloying with subsequent pressing and considered as models of nonmetallic inclusions in carbon steels and siliceous cast irons. In an acidic sulfate solution, silicocarbide is highly active in hydrogen reduction and iron ionization in the active dissolution range. Therefore, the corrosion resistance of silicocarbide in acids is lower compared to iron and cementite, which is caused by the peculiarities of its crystal structure. In a neutral borate solution both on silicocarbide and cementite, two anodic peaks are observed that are caused by the dissolution of the corresponding phase and the additional oxidation of the passive film, which is characterized by the heightened defectiveness because of the carbon accumulation. Silicocarbide has lower dissolution currents compared to cementite and a higher resistance to the local activation and depassivation, which is caused by the presence of a superficial layer enriched in SiO₂.     

Electrochemical synthesis of polypyrrole nanowires in the presence of gelatin

Biotemplating is an emerging, unique approach for the synthesis and organization of the organic or inorganic materials into well-defined nanostructures. In this article, conducting polymer polypyrrole (PPy) nanowires were electrochemically synthesized using a protein molecule, gelatin, as a template. The morphologies, microstructures, chemical compositions, and electrochemical performances of the obtained nanowires were investigated in detail. It was found that the gelatin played an important role in the formation of the PPy nanowires and the morphologies of the nanowires were closely related to the electrodes used. This work not only extended the application of gelatin to the synthesis of the conducting polymer nanowires, but also presented a simple and useful route to the fabrication of PPy nanowires with different length, from normal size to superlong size.     

锌电沉积过程中锗的电化学行为

采用线性扫描伏安技术、交流阻抗技术和计时电流法研究锗在锌电沉积过程中的电化学行为,结合Zn-H2O系和Ge-H2O系E-pH图从热力学角度进行分析.结果表明:锗会削弱锌电沉积阴极极化,且随着电解液中锗浓度的增加,去极化作用增强,而且锗会引起电荷传递电阻的降低,改变锌电沉积电荷传递步骤,加剧氢还原反应的发生.     

The protective effect of polypyrrole coating on the corrosion of steel electrode in acidic media

In this study, the corrosion parameters of stainless steel containing 12% Cr, have been determined by Tafel extrapolation method in 1 M HCl, H₂SO₄ and H₃PO₄ media. Later, steel was coated with polypyrrole in 0.1 M Pyrrole + 0.3 M Oxalic acid solution by cyclic voltametric method. The corrosion parameters and percentage inhibition efficiencies of coated electrodes were investigated according to immersion times in the same media. In all acidic media studied, increases in immersion time, produced increased corrosion densities and a decrease in percentage inhibition efficiencies were determined.     

Electrochemical synthesis of polypyrrole on aluminium in different anions and corrosion protection of aluminium

In this study, polypyrrole was deposited on the aluminium in different anions (CO₃²⁻, NO₂⁻, CrO₄²⁻, DBS⁻). The contribution of anions to formation of polypyrrole film was investigated by using cyclic voltammetry (CV) technique. The effect of polypyrrole film on the corrosion of aluminium was searched in 0.1 M HCI solution by using potentiostatic method. For this purpose, polarization curves were obtained, corrosion current density (icorr), corrosion potential (Ecorr), polarization resistance (Rp) were determined from the polarization curves. Moreover, the percent efficiency of coating was calculated. The complexes of pyrrole pentamers and different anions (CO₃²⁻, NO₂⁻, CrO₄²⁻, DBS⁻) were studied using ab initio quantum chemical at the Hartree-Fock (HF) levels with STO-3G, 3-21G, 6-31G(d,p) [13] basis sets and HOMO-LUMO energy gap is calculated by B3LYP method with 3-21G* and 6-31G(d,p) basis sets. The polypyrrole film obtained in CrO₄²⁻ anion is determined to be the most effective in prevention to pitting corrosion of aluminium as experimental and theoretical.     

Electrochemical and chemical characterization of polypyrrole/phosphotungstate coatings electrosynthesized on carbon steel electrodes in acetonitrile medium

Hybrid material polypyrrole/PW₁₂O₄₀³⁻ was potentiostatically electrosynthesized on carbon steel electrodes in acetonitrile medium. The obtained coatings were characterized by cyclic voltammetry, FTIR-ATR, XPS, SEM and EDX techniques. Phosphotungstate as dopant agent, Fe oxides and polypyrrole chains are the compounds that form the hybrid material structure. The influence of the electrosynthesis potential was analysed. Oxidized and reduced state of the coatings was also studied. When the electrosynthesis potential is increased up to 2.00 V and the polymeric coatings are in reduced state, the covering degree is very high and the coatings present a very homogenous and uniform surface.     

Electrochemical synthesis of polypyrrole for the immobilization of galactose oxidase

Based on the results of the atomic force microscopy (AFM) experiment, the images of the polypyrrole films are modified, which are dependent on the composition of the pyrrole solution for electrolysis and the method of electrolysis. Only one kind of polypyrrole film, which is synthesized using repeated potential cycling in the solution consisting of 0.1 M pyrrole and 1 M NaCl with pH 2, can be used for the immobilization of galactose oxidase. The Raman spectra of the polypyrrole galactose oxidase electrode show a characteristic peak of the amino acid, which is evidence for galactose oxidase immobilized in the polypyrrole film. The enzyme electrode has a bioelectrochemical response to galactose; its response current increases linearly with increasing concentration of galactose in the range below 2 mM. Thus, this enzyme electrode can be used to determine galactose concentration.     

High potential cathodic polarization of oxidized aluminium electrodes in neutral and acid media

The cathodic polarization of an oxidized 99.9995% aluminium electrode at potentials from −2 to −2.5 V(SCE) in several electrolytes of neutral and acid pH values has been studied. Potentiodynamic oxidation of cathodically polarized aluminium electrodes following the technique of Rozenfel'd et al. have been performed and analyzed. In solutions of pH 1–2.1, the oxide film present on the aluminium surface is partially removed by means of a continuous cathodic polarization at those potentials; there is evidence of a small amount of oxide formation following oxide removal and metal etching. The cathodic behaviour in acid and neutral media is interpreted on the basis of a local alkalization resulting from the H₂ evolution. A possible mechanism for the oxide removal is discussed.     

Measurements of pitting corrosion currents of zinc in near neutral media

Using a simple model cell the susceptibility of the zinc electrode to pitting corrosion by SO₄²⁻, SO₃²⁻, S₂O₃²⁻ and S²⁻ anions were examined in naturally aerated carbonate solutions. It was found that, pitting started after an induction period, τ, which depended on the type and concentration of the aggressive and passivating anions. The pitting corrosion current increased with time until steady state values were attained. These values depended on both the type and the concentration of the passivating and pitting anions. For the same concentration of the passivating anions, the corrosion current varied with the concentration of the aggressive anion according to the relation: logi_pit.=a₁+b₁logC_agg. At a constant concentration of the aggressive anion, the corrosion current varied with the concentration of the passivating anions according to: logi_pit.=a₂−b₂logC_pass. The constants a₁ (a₂) and b₁ (b₂) were determined for all the systems studied. From the values of a₁ the corrosivity of the sulphur-containing anions is found to decrease in the order SO₄²⁻>SO₃²⁻>S₂O₃²⁻>S²⁻.     

Control of zinc corrosion in acidic media: Green fenugreek inhibitor

Fenugreek seeds extract was examined as a green corrosion inhibitor for Zn in 2.0 mol/L H₂SO₄ and 2.0 mol/L HCl solutions by mass loss and electrochemical measurements. Scanning electron microscope (SEM) images show that the surface damage is decreased in the presence of the inhibitor. X-rays photoelectron spectroscopy (XPS) analysis was performed to identify the corrosion product, ZnO, and to prove the inhibitor adsorption mechanism. The maximum inhibition efficiency values are 90.7% after 1 h and 66.6% after 0.5 h by 200 mL/L of fenugreek extract in H₂SO₄ and HCl solutions, respectively. Addition of I⁻ ion greatly improves the inhibition efficiency of fenugreek seeds extract for Zn corrosion in HCl due to the synergistic effect. Potentiodynamic polarization and EIS measurements prove the inhibition ability of fenugreek for Zn corrosion in HCl as indicated by the decreased corrosion current density and increased charge transfer resistance values in the presence of fenugreek.     

Corrosion and stress corrosion cracking of amorphous FeNiMoxB alloys in several neutral and acidic media

Corrosion and stress corrosion cracking behaviour of a series of amorphous iron alloys FeNiMo_xB (x = 0, 2, 4, 8.5) has been investigated in several neutral and acidic media. In particular in aqueous solutions of ferric chloride, potassium tetrathionate and sulphuric acid containing chlorides stress corrosion cracking (SCC) has been studied by means of constant strain tests and corrosion rates have been evaluated by means of weight loss measurements. In several cases polarization curves have been recorded in order to clarify the electrochemical behaviour of the amorphous alloys. SEM observations of the fracture surfaces have been performed. It has been observed that the glassy alloys under investigation are susceptible to SCC at free corrosion potential in all the environments. SCC has been observed on specimens cathodically and anodically polarized in sulphuric acid containing chlorides. Hydrogen embrittlement can reasonably be considered responsible of the SCC phenomenon, except in sulphuric acid solution on specimens anodically polarized and in iron chloride solution. A deleterious effect of molybdenum has been noted on the corrosion rates of unstressed specimens and on the time to failures of stressed samples.     

Electrochemical characteristics of iron in acidic solutions containing some organic sulphur compounds

Corrosion inhibition of bis-n-butyl-sulphinylmethane, bis-n-butyl-sulphonylmethane and ethylene oxide condensates of 2,2′-dihydroxy-n-hexylsulphide on iron in sulphuric and hydrochloric acids was measured by using electrochemical methods. These compounds were excellent inhibitors for acidic corrosion of iron and inhibited the cathodic and the anodic corrosion reactions.     

Use of polymeric ionic liquids as stabilizers in the synthesis of polypyrrole organic dispersions

Polypyrrole dispersions in several organic media were synthesized by using polymeric ionic liquids (PILs) both as steric stabilizers and as phase transfer agents. Firstly, PPy aqueous dispersions were prepared by polymerizing pyrrole in the presence of poly(1-vinyl-3-ethylimidazolium bromide) as steric stabilizer. By addition of different salts: lithium triflate, bis(trifluoromethane)sulfonimide lithium salt, bis(pentafluoroethane)sulfonimide lithium salt, dodecylbenzenesulfonic acid sodium salt and p-toluene-4-sulfonic acid monohydrate, the polymeric stabilizer becomes hydrophobic, precipitating in water and trapping the PPy dispersed microparticles inside. Polypyrrole organic dispersions were obtained by dispersion of the corresponding powders in a variety of organic solvents such as methanol, N,N-dimethylformamide (DMF), acetone, tetrahydrofurane (THF), butanone and toluene. The dispersability or non-dispersability of the PPy powders in each of the organic solvents depended on the nature of the added coagulating salt. Characterization of the PPy organic dispersions by photon correlation spectroscopy and atomic force microscopy (AFM) showed individual particles with sizes between 100 and 400 nm. After casting the organic dispersions, the films showed a granular nanostructured surface and electrical conductivity values as high as 10⁻¹ S/cm.