The inductive behavior derived from hydrolysis of polyaniline

Electrochemical impedance spectroscopy (EIS) was used to study the impedance characteristics of polyaniline (PANI) films deposited by cyclic voltammetry with different anodic potential limits. The presence of benzoquinone (BQ) as hydrolysis product of PANI was evident for PANI films deposited with anodic potential limits ≥0.80 V. The data from EIS for PANI film with inbuilt BQ reveals an inductive behavior. The existence of inductive behavior for PANI film under different applied bias potentials was brought out through fitting of EIS data with equivalent circuits and deducing the value of an inductor element (L). The inductive behavior was attributed to arise due to the presence of BQ within PANI films and adequately supported by the results from X-ray photoelectron spectroscopy (XPS). The value of L reaches saturation for the PANI film synthesized with an upper potential limit of 0.90 V and measured at 0.70 V. The EIS and XPS results of the poly(N-methylaniline) (PNMA) film prepared under similar conditions corroborated with the observation that the presence of BQ within PANI results inductive characteristics to PANI     

Fluorinated functionalized EDOT-based conducting films

Three ethylenedioxithiophene (EDOT) derivatives bearing either perfluoro- or ether perfluoro-alkyl chains were synthesized with the objective to prepare films with dry and chemically immobilized lubrication properties. The corresponding fluorinated PEDOT films were deposited on platinum surface by electropolymerization. Cyclic voltammetry (CV) and electrochemical quartz crystal microbalance (EQCM) analyses (both quartz resonant frequency and resonant admittance) of the growing steps are described. The electroactive behavior of the films versus their doping level was followed by electrochemical impedance spectroscopy (EIS) through equivalent circuit fitting procedure and compared to their CV responses. Hysteresis in fit parameters corresponding to capacity and film resistance between the forward and the backward scans are observed and discussed. Control of the chemical structures and charge effects on PEDOT chains are followed by an XPS analysis. From these analyses, it appears that the fluorinated side-arm does not alter both the growing and the electrical properties of the films in respect to the pristine PEDOT taken as reference.     

Polyaniline fibres as electrodes.: Electrochemical characterisation in acid solutions

Polyaniline fibre microelectrodes prepared from a doped solution of polyaniline protonated with 2-acrylamido-2-methyl-1-propanesulphonic acid in dichloracetic acid were characterized electrochemically for the first time. Low scan rate cyclic voltammetry was used for characterisation in different acid electrolyte solutions, hydrochloric, nitric, perchloric, sulphuric and phosphoric, at low pH values with varying positive potential limits. Electrochemical impedance spectroscopy was also utilised. The electrochemical behaviour of polyaniline (PANI) fibres was found to be similar to that of PANI films obtained by electropolymerisation on metallic electrode substrates. The conduction potential window was found to be from +0.20 to +0.60 V versus SCE, with small variations in the different acid solutions as well as with pH. The standard electrochemical redox couple hexacyanoferrate(III), was found to behave quasi-reversibly in the conduction potential region and rate constants were evaluated.     

Polyaniline-deposited porous carbon electrode for supercapacitor

Electrodes for supercapacitors were fabricated by depositing polyaniline (PANI) on high surface area carbons. The chemical composition of the PANI-deposited carbon electrode was determined by X-ray photoelectron spectroscopy (XPS). Cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS) were used to investigate the electrochemical properties of electrodes. An equivalent circuit was proposed to successfully fit the EIS data, and the significant contribution of pseudocapacitance from PANI was thus identified. A comparative analysis on the electrochemical properties of bare-carbon electrodes was also conducted under similar conditions. The performance of the capacitors equipped with the resulting electrodes in 1 M H₂SO₄ was evaluated by constant current charge-discharge cycling within a potential range from 0 to 0.6 V. The PANI-deposited electrode exhibits high specific capacitance of 180 F/g, in comparison with a value of 92 F/g for the bare-carbon electrode.     

EIS investigation of passive film formation on mild steel in oxalic acid solution

The properties of oxide films on mild steel formed anodically in aqueous solution containing oxalic acid were investigated by means of electrochemical impedance spectroscopy (EIS). The morphology of the passive layers at different stages of film formation was investigated using scanning electron microscopy (SEM). Passivation of mild steel in oxalic acid solution is a multi-stage process that occurs before passive layer breakdown. The influence of potential on the electrochemical behavior of the passive layer was also investigated. Depending on the passive layer potential, the EIS spectra obtained exhibited a one- or two-time constant system. This suggests the formation of either a one layer or two layer oxide film on the mild steel surface, depending on the passivation potential.     

Characterization of conducting poly(3‐methylthiophene) films prepared under sono‐electrochemical conditions

Poly(3‐methlthiophene) films were prepared under “silent” and “sono‐electrochemical” potentiostatic (SEP) conditions. A three‐electrode one‐compartment sono‐cell was used with a working platinum disc electrode. The sono‐electrochemically formed polymer films were deposited with different working electrode‐to‐horn distances. The composition, electrochemical, spectroscopic, and morphological characteristics of the resulting polymer films were determined. Elemental analysis, FTIR‐spectra, and X‐ray photoelectron spectroscopy (XPS) data proved that the polymer films prepared under SEP conditions have predominant α‐α′‐couplings between the 3MT units, and the aromatic ring integrity is maintained in the film. Scanning electron microscopy showed that those films are more compact and less porous compared to the films prepared under silent conditions. The use of sono‐irradiation during electropolymerization enhanced the diffusion of the monomer units towards the electrode surface and resulted in relatively less doped polymers with less conductivity. Electrochemical impedance spectroscopy (EIS) data for films prepared under silent and SEP conditions were collected in a monomer‐free solution. The results show that the impedance of SEP films is relatively higher than those prepared under silent conditions, and a combination of charge transfer kinetics with diffusion‐controlled conduction mechanism within the films. The diffusion was found to be a function of the porosity of the film. Conductivity measurements are in good agreement with EIS, elemental analysis, and XPS data. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 102: 2416–2425, 2006     

Electrochemical impedance study of polyaniline electrocoated porous carbon foam

Electropolymerization of aniline on mesophase pitch based carbon foam has been studied in order to evaluate the influence of conductive polymer coating on the properties of carbon foam. The surface morphology of the coating was determined by scanning electron microscopy (SEM). Cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS) were used to investigate the electrochemical properties of resulting modified carbon foam samples. Polyaniline (PANI) electrocoated-mesophase pitch based carbon foam showed good capacitor behavior in 0.5 M H₂SO₄. Better capacitive behavior is obtained for 100 and 150 mV/s compared to other scan rates, under these faster scan rates thinner films of PANI coatings were combined with more porous structure of carbon foam. Conductivity of the carbon foam was increased from 9.23 to 13.73 S/cm by electrocoating of PANI.     

单极脉冲电合成聚苯胺膜及其超级电容性能

采用单极脉冲电化学聚合方法在铂基体表面制备了具有三维网络结构的聚苯胺(PANI)纳米纤维膜。采用傅里叶变换红外(FT-IR)光谱和扫描电镜(SEM)分析比较了脉冲聚合和循环伏安聚合膜的组成和形貌,在0.5mol·L-1的硫酸溶液中通过恒电流充放电和电化学阻抗(EIS)等考察了聚合膜的电化学容量性能。研究表明,固定脉冲电压1.0V、苯胺单体浓度0.2mol·L-1时控制单极脉冲频率1.25s-1、占空比50%可获得高达699F·g-1比电容的纳米纤维结构PANI膜;聚合膜呈现均匀的三维有序网络状分布,其离子交换容量、循环稳定性及超级电容性能远高于循环伏安法聚合的PANI膜。     

Methacryloxypropyltrimethoxysilane films on aluminium: Electrochemical characteristics, adhesion and morphology

The electrochemical characteristics, adhesion and morphology of methacryloxypropyltrimethoxysilane (MAPT) films on aluminium were investigated during exposure to 3 wt.% NaCl. The MAPT films were deposited on aluminium surface from 2 to 5 vol.% methacryloxypropyltrimethoxysilane solutions, with the aim to investigate the influence of deposition parameters (silane solution concentration and curing time) on electrochemical characteristics, adhesion and morphology of MAPT films on aluminium.Using electrochemical impedance spectroscopy (EIS), potential–time measurements, adhesion measurements and optical microscopy coupled with image analysis, it was shown that films deposited from 5 vol.% solution exhibited better corrosion stability and adhesion, as well as lower porosity comparing to 2 vol.% solution and improved the corrosion protection of aluminium substrate, while the curing time had no influence on these characteristics.     

Electropolymerization, characterization and corrosion performance of poly(N-ethylaniline) on copper

Poly(N-ethylaniline) (PNEA) coatings were grown by cyclic voltammetry technique on copper from 0.1 M N-ethylaniline (NEA) in 0.3 M oxalic acid solution. The optimum conditions (e.g. upper potential limit, scan rate and cycle number) effect on corrosion performance of synthesized PNEA films were determined in order to obtain best protection results against corrosion. The electrodeposited coatings were characterized by cyclic voltammetry (CV), Fourier Transform Infrared-Attenuated Total Reflectance (FTIR-ATR) spectroscopy and scanning electron microscopy (SEM). Redox parameters were found after electrochemical tests and results of stability tests of these films impart an electroactive behavior that is composed of both diffusion control and thin film behavior. In addition, corrosion performance of PNEA coatings were investigated in 0.1 M H₂SO₄ by Tafel extrapolation and electrochemical impedance spectroscopy (EIS) techniques.     

Styrene butadiene co-polymer based conducting polymer composite as an effective corrosion protective coating

Electroactive conducting polymer composite coatings of polyaniline (PANI) are electrosynthesized on styrene–butadiene rubber (SBR) coated stainless steel electrode by potentiostatic method using aqueous H₂SO₄ as supporting electrolyte. The protective behaviour of these coatings in different corrosion media (3.5% NaCl and 0.5 M HCl) is investigated using Tafel polarization curves, open circuit potential measurements and electrochemical impedance spectroscopy. The results reveal that SBR/PANI composite coating is much better in corrosion protection than simple PANI coating. The corrosion potential of composite films shifts to more noble values indicating that SBR/PANI composite coating act as an effective corrosion protective layer.     

The effect of thickness on the composition of passive films on a Ti-50Zr at% alloy

Anodic films were grown potentiodynamically in different electrolytes (pH = 1-14) on a Ti-50Zr at% cast alloy, obtained by fusion in a voltaic arc under argon atmosphere. The thickness of the films was varied by changing formation potential from the open circuit potential up to about 9 V; growth was followed by 30 min stabilization at the forming potential. Films having different thicknesses were characterized by photocurrent spectroscopy (PCS) and electrochemical impedance spectroscopy (EIS). Moreover, film composition was analyzed by X-ray photoelectron spectroscopy (XPS).Regardless of the anodizing conditions, passive films on the Ti-50Zr at% alloy consist of a single layer mixed oxide phase containing both TiO₂ and ZrO₂ groups. However, an enrichment of Ti within the passive film, increasing with the film thickness, is detected both by PCS and XPS. This leads to concentration profiles of Ti⁴⁺ and Zr⁴⁺ ions along the thickness, and to different electronic properties of very thin films (more insulating) with respect to thicker films (more semiconducting), as revealed by the photocurrent-potential curves.     

Electrochemically polymerized 2,2-dimethyl-3,4-propylenedioxythiophene on carbon fiber for microsupercapacitor

ProDOT(Me)₂ was electrochemically polymerized onto a carbon fiber microelectrode (CFME) by cyclovoltammetry under a wide potential range (0–1.6 V) with well-defined parameters. The nano to micron scale coatings on CFMEs were characterized by cyclovoltammetry, ex situ FTIR attenuated total reflectance spectroscopy (FTIR-ATR), electrochemical impedance spectroscopy (EIS) and scanning electron microscopy (SEM and EDX). The existence of a capacitance behavior is shown by Nyquist, Bode phase relationship.     

Plasma-polymerized coatings of trimethylsilane deposited on cold-rolled steel substrates Part 2. Effect of deposition conditions on corrosion performance

Trimethyl silane (TMS) plasma-polymerized films were deposited on cold-rolled steel (CRS) under different conditions. The films were characterized by angular-dependent X-ray photoelectron spectroscopy (XPS), Auger electron spectroscopy (AES) and time-of flight secondary ion mass spectrometry (TOFSIMS). The complementary information generated by these surface techniques gave detailed information on the film composition. The corrosion performance of the plasma films was estimated by electrochemical impedance spectroscopy (EIS) and by exposure in a humidity test. All films were Si-based and their composition was a function of the deposition conditions and the plasma cleaning of substrate prior to deposition. A reducing plasma for metal surface treatment resulted in a film with the highest impedance. The plasma film surfaces were highly oxidized. The contact angle was the lowest for plasma films deposited from a mixture of TMS and oxygen and their corrosion performance was the poorest.     

Electrochemical behavior of the Ti–6Al–4V alloy coated with a-C:H films

In this work diamond-like carbon films were deposited on the Ti–6Al–4V alloy, which has been used in aeronautics and biomedical fields, by electrical discharges using a magnetron cathode and a 99.999% graphite target in two different atmospheres, the first one constituted by argon and hydrogen and the second one by argon and methane. Films deposited using the argon/hydrogen mixture were called a-C:H, while films deposited using the argon/methane mixture were called DLC. Raman spectroscopy was used to study the structure of the films. The Raman spectra profile of the a-C:H films is quite different from that of the DLC films. The disorder degree of the graphite crystalline phase in a-C:H films is higher than in DLC films (a-C:H films present small values for the the I_D/I_G ratio). Potentiodynamic corrosion tests in 0.5 mol l⁻¹ NaCl aqueous solution, pH 5.8, at room temperature (≈25 °C) were carried out as for the a-C:H as for the DLC coated surfaces. Comparison between the corrosion parameters of a-C:H and DLC coated surfaces under similar deposition time, showed that DLC coated surfaces present bigger corrosion potential (E_corr) and polarization resistance than those coated with a-C:H films. Electrochemical impedance spectroscopy (EIS) was also used to study the electrochemical behavior of a-C:H and DLC coated surfaces exposed to 0.5 mol l⁻¹ aqueous solution. The EIS results were simulated with equivalent electrical circuit models for porous films. The results of these simulations showed similar tendency to the one observed in the potentiodynamic corrosion tests. The DLC film resistance and the charge transfer resistance (R_ct) for the DLC coated surface/electrolyte interface were bigger than the ones determined for the a-C:H coated surfaces.     

Electrochemical oxidation of histidine at an anodic oxidized boron-doped diamond electrode in neutral solution

Electrochemical oxidation of histidine (His) at an anodic oxidized boron-doped diamond electrode (AOBDDE) was performed. A significant peak of His oxidation is observed at about +1.5 V vs. Ag/AgCl, however, the response current was inhibited due to strong His-oxidized product adsorption onto the electrode surface. The characteristics of the His-oxidized product adsorbed onto the electrode surface were investigated by studying the electrochemical behavior of the Fe(CN)₆⁴⁻ redox reaction using cycle voltammetry (CV) and electrochemical impedance spectroscopy (EIS). Both CV and EIS results showed a decrease in the sum of transfer coefficients and an increase in the electron transfer resistance, which indicate that the adsorption film is a non-conductive film. The most possible active site locations for the AOBDDE for His oxidation are within these low-lying polycrystallite AOBDDE surface regions. The results from Raman and X-ray photoelectron spectroscopy offer strong evidence of the imidazole ring reaction from His. Experiments confirmed that the adsorbed film can be removed and the electrode surface reactivated using brief polarization at +2.5 V.     

Corrosion resistance of pulsed laser-treated Ti-6Al-4V implant in simulated biofluids

A commercial Ti-6Al-4V alloy was treated with a pulsed-wave Nd:YAG laser under various process conditions to obtain surface oxide layer for corrosion resistance. The corrosion behaviors of bare and laser-treated Ti-6Al-4V alloy exposed to three different simulated biofluids (SBFs), namely, (1) NaCl solution, (2) Hank's solution, and (3) Cigada solution, were studied by using the electrochemical techniques like open circuit potential (OCP), Tafel analysis, and electrochemical impedance spectroscopy (EIS). The Tafel analysis showed that the laser-treated Ti-6Al-4V specimens were more corrosion resistant than the bare specimens in any of the above SBFs. The various electrical equivalent circuit models were applied to fit the EIS results to further understand corrosion mechanisms due to different surface layers formed on the alloy surface before and after the laser treatment. Optical and AFM imaging techniques were used to evaluate the topographic and morphologic features of the alloy exposed to such SBFs. The corrosion behavior of the laser-treated surfaces was explained by the melting and solid-state oxidation processes, the morphology of the surface oxide, and the underlying alloy microstructure. It is realized during the present investigation that better corrosion resistance and surface stability can be achieved by oxide growth in solid-state, under a pulsed laser condition.     

Inhibition of nickel coated mild steel corrosion by electrosynthesized polyaniline coatings

Polyaniline (PANI) coatings were electrochemically synthesized on nickel (Ni) coated mild steel (MS) and their corrosion protection properties were investigated. In this work, the Ni layer (∼1 μm thick) was electrodeposited on MS under galvanostatic condition. Thereafter, the PANI coating was deposited over the Ni layer from aqueous salicylate medium by using cyclic voltammetry. These bi-layered composite coatings were characterized by cyclic voltammetry, UV–vis absorption spectroscopy and Fourier transform infrared (FTIR) spectroscopy. The corrosion protection properties of Ni coated MS (Ni/MS) and PANI coated Ni/MS (PANI/Ni/MS) were investigated in aqueous 3% NaCl by using open circuit potential (OCP) measurements, potentiodynamic polarization technique and electrochemical impedance spectroscopy (EIS). It was shown that the top layer of PANI exhibits a lower porosity behavior with respect to Ni coating and reduces the corrosion rate of Ni/MS almost by a factor of 3500 and increases the lifetime of Ni coating.     

Investigation of solid oxide fuel cell short stacks for mobile applications by electrochemical impedance spectroscopy

Solid oxide fuel cells (SOFC) for mobile applications are developed and investigated at the German Aerospace Center (DLR) in Stuttgart. Therefore a light-weight stack design was developed in cooperation with the automotive industry (BMW/Munich, Elring-Klinger/Dettingen, ThyssenKrupp/Essen) and the Research Center Jülich (FZJ). This concept is based on the application of stamped metal sheet bipolar plates, into which the SOFC cells are integrated by brazing technology. For the development and the investigation of the SOFC cells and short stacks, the electrochemical impedance spectroscopy (EIS) is an important and useful characterization method. The paper concentrates on the investigation and on the electrochemical testing of the SOFC short stacks with sintered anode-supported cells (ASC). The short stacks were electrochemically characterized mainly by electrochemical impedance spectroscopy, by current-voltage measurements and by long-term measurements. The cells and stacks were operated at different temperatures, varying fuel gas compositions, different fuel gas flow rates and at different electrical current loads. The influence of these operating conditions on the electrochemical performance of the short stacks is outlined. The nature of losses, e.g. ohmic and the polarization resistances of the electrodes were examined and determined by fitting of the impedance spectra to an equivalent circuit.     

海藻酸钠的浓度对聚苯胺/海藻酸钠电化学性能的影响

以海藻酸钠(SA)为软模板,采用原位氧化聚合法制备了聚苯胺/海藻酸钠(PANI/SA)电极材料,研究了SA的浓度对其结构、形貌及电化学性能的影响。利用傅里叶变换红外光谱(FTIR)和扫描电镜(SEM)对所制PANI/SA的结构和形貌进行了表征。在1 mol/L H2SO4溶液中,通过循环伏安法(CV)、恒电流充放电(CD)和交流阻抗法(EIS)测试了电极材料的电化学性能。结果表明:PANI/SA的比电容随聚合体系中SA质量分数的增大先升高后降低,w(SA)=0.01%时,PANI/SA为由纳米纤维相互交织缠绕的网状结构,其比电容最高(459.7F/g),较纯PANI提高了20.8%。