Reticulated vitreous carbon/polypyrrole composites as electrodes for lithium batteries: Preparation,electrochemical characterization and charge–discharge performance

Polypyrrole (PPy) composites were prepared via electrochemical deposition onto reticulated vitreous carbon (RVC) – a tridimensional material – and tested as cathodes in lithium batteries. Different RVC/polypyrrole electrodes were prepared and characterized: PPy doped with ClO₄^? (RVC/PPy) as an anion-exchanger film; PPy doped with a large anion – poly(styrenesulphonate) – (RVC/PPyPSS) as a cation-exchanger film; and a bi-layer polymeric film formed by an inner layer of the former and an outer layer of the latter (RVC/PPy/PPyPSS). Photomicrographies, voltammetric profiles and electrochemical impedance spectroscopy data have shown different morphological and electrochemical characteristics for polypyrrole doped with small or large anions, and a peculiar behavior for the bi-layer electrodes. Charge/discharge results indicated that the RVC/PPy electrode can attain specific capacities as high as 95 mAh g^?1. PSS-doped polypyrrole electrodes also presented high specific-capacity values when the bi-layer configuration (RVC/PPy/PPyPSS) and lower charge–discharge currents were used. Impedance data indicated that the counter-ion diffusion within the bi-layer is hindered, which explains the slower activation of this composite when compared to that of RVC/PPy.     

Electrochromism of poly(pyrrole) film on Au nano-brush electrode

Au nano-brush membranes were prepared by a modified template method. Poly(pyrrole) (PPy) films were immobilized by an electropolymerization with the product membrane as the working electrode. In contrast to the PPy film on an Au planar electrode, the PPy film on the nano-brush electrode showed a higher electrochemical stability for the continuous cyclic polarization. Based on the measurement of the reflectance using a simple two-electrode device, a fine electrochromic performance including the switching response and repetition stability was obtained from the device with the PPy film on the Au nano-brush electrode.     

Influence of dopant ions on properties of conducting polypyrrole and its electrocatalytic activity towards methanol oxidation

The polypyrrole (PPy) films were deposited on vacuum metallized substrates by electro-oxidation of pyrrole monomer. These electrodes were then modified with a range of metal halides having different electronegativities. The modified polypyrrole electrodes were employed to investigate electrocatalytic activity towards methanol electrochemical oxidation by means of cyclic voltammetry in 0.1 M HClO₄ as supporting electrolyte. It was found that the electronegativity of the dopant ion incorporated in the PPy film governs the electrocatalytic activity towards methanol oxidation. Among different dopant anions used in the present work, the PPy doped with zirconium chloride gave the highest anodic current of 10 mA cm⁻² at the oxidation potential of methanol. Electrical property and the charge created due to doping in the polymers were measured using X-ray photoelectron spectroscopy (XPS) and Electron spin resonance spectroscopy (ESR). Electrocatalytic activity of the modified electrodes was correlated with various factors obtained from different polymer characterization experiments. The results were explained on the basis of the charge-transfer efficiency at the electrodeelectrolyte interface, which was associated with the acceptor state created by the dopant in the semi-conducting polymer.     

Electrocatalytic oxidation of ascorbic acid at polypyrrole nanowire modified electrode

Polypyrrole (PPy) nanowire modified electrodes were prepared electrochemically by template-free method based on graphite electrodes. The freshly prepared electrodes were dipped in 10% HClO₄ solution at least 24 h for removal of carbonate ions. The modified electrodes toward ascorbic acid were characterized by potentiostatic method. The experiment's results show that the PPy modified electrodes have obvious electrocatalytic effect toward ascorbic acid oxidation. The oxidation current density has a good linearity in the concentration range of 5.0 × 10⁻⁴ and 2.0 × 10⁻² mol L⁻¹ of ascorbic acid. The determination sensitivity may be significantly affected by the thickness of PPy film and pH of the test solution. The method has promising application in determination of ascorbic acid in the real samples.     

Electrocatalytic oxidation of methanol on Pt modified polyaniline in alkaline medium

A comparative study of the electrocatalytic oxidation of methanol is made in NaOH, Na₂CO₃ and NaHCO₃ on bare Pt (Pt), polyaniline covered Pt (PANI) and Pt modified polyaniline film on Pt (Pt/PANI) using cyclic voltammetry, polarization, ac impedance spectroscopy and chronoamperometric techniques at 25 °C. The cyclic voltammetry and polarization studies show that the potentials at which methanol oxidation commences on different electrodes in each of the alkaline medium examined follow the trend Pt/PANI < Pt < PANI whereas the potentials for initiation of oxidation on each electrode in different alkaline media follow the order NaHCO₃ > Na₂CO₃ > NaOH. The oxidation current is highest and charge transfer resistance lowest for Pt/PANI films compared to Pt in all the media studied. However, for the same Pt loading Pt/PANI films exhibit larger oxidation currents in NaOH followed by Na₂CO₃ and NaHCO₃. The Tafel slope for methanol oxidation on Pt/PANI in NaOH, Na₂CO₃ and NaHCO₃ has a value of about 115 mV decade⁻¹. The chronoamperometric response of the Pt/PANI film at the peak potential for methanol oxidation shows lesser sensitivity to poisoning by CO compared to bare Pt and platinised Pt (Pt/Pt).     

Corrosion protection of molybdate doped polypyrrole film prepared in succinic acid solution

ABSTRACT

Polypyrrole (PPy) was prepared on the mild steel substrate by electrochemical polymerisation in the solution containing pyrrole monomer and succinic acid. The mild steel surface could be passivated before and during electropolymerisation by molybdate. The morphology and structure of the PPy film were studied with SEM. The typical cauliflower structure of PPy was observed. Raman and IR spectroscopy showed that the obtained PPy was in an oxidised state. The thermal stability of PPy was investigated by the thermal gravimetric analysis, showing that PPy was stable at higher than 480°C. The electrochemical property of the PPy film was performed by open circuit potential, polarisation curves (I/E), and electrochemical impedance spectroscopy. The corrosion behaviour of mild steel (CT3) with PPy film in solution NaCl 3% was studied.

This paper is part of a supplementary issue from the 17th Asia-Pacific Corrosion Control Conference (APCCC-17).     

Tris(trifluoromethylsulfonyl)methide-doped polypyrrole as a conducting polymer actuator with large electrochemical strain

A free-standing polypyrrole (PPy) film actuator, prepared electrochemically from a methyl benzoate solution of 1,2-dimethyl-3-propylimidazolium tris(trifluoromethylsulfonyl)methide (DMPIMe), exhibited up to 36.7% electrochemical strain in a propylene carbonate (PC)/water solution of lithium bis(nonafluorobutylsulfonyl)imide, Li(C₄F₉SO₂)₂N (LiNFSI). The maximum electrochemical strain of Me-doped PPy film depended on the electrolyte used for driving the Me-doped PPy actuator. When a PC/water mixed solution of lithium bis(trifluoromethylsulfonyl)imide (LiTFSI) was used as the driving electrolyte, the maximum electrochemical strain, measured by cycling between −0.9 and +0.7 V versus Ag/Ag⁺ at 2 mV s⁻¹, was 24.2%, smaller than that (30.0%) driven with LiNFSI. When a PC/water suspension of DMPIMe was used as the driving electrolyte, the maximum electrochemical strain was 31.9%. However, the response speed of Me-doped PPy actuator driven with DMPIMe was slower than those driven with Li(C_nF_2n+1SO₂)₂N, due presumably to the size and shape of the anions. The addition of CF₃COOH in electrolytic solutions for electropolymerization increased the maximum electrochemical strains (36.7% and 36.6%) of Me-doped PPy actuator driven by using a PC/water solution of LiNFSI and a PC solution of DMPIMe, respectively.     

The Mechanism of the Cobalt Anodic Ionization in Chloride Solution

The mechanism of the cobalt anodic ionization in 2.5 M CoCl₂ solution (pH 3.5 ± 0.2, t = 15–60°C) is studied with the use of rotating disk electrode and rotating ring-disk electrode methods. The experimental data showed that the ionization proceeds by stages, of which the first is an intermediate CoA_ads species formation (A is Cl⁻ or OH⁻), in which the cobalt oxidation state is 1+. Further CoA_ads transformation involves rapid parallel reactions of the Co⁺ ions electrochemical oxidation or disproportionation. An oxidation current wave was revealed at the platinum ring electrode for the species formed during the cobalt anodic ionization at the disk electrode. Judging by the wave potential, these species can be either finely dispersed elemental cobalt or the intermediate Co⁺ ions.__________Translated from Zashchita Metallov, Vol. 41, No. 4, 2005, pp. 381–385.Original Russian Text Copyright © 2005 by Manilevich, Kozin, Bogdanova, Danil’tsev.     

Doped and de-doped polypyrrole nanowires by using a BMIMPF6 ionic liquid

We electrochemically synthesized π-conjugated polypyrrole (PPy) nanowires by using an environmentally stable and recyclable ionic liquid, 1-butyl-3-methylimidazolium hexafluorophosphate (BMIMPF₆), as a dopant, based on an anodic alumina oxide (Al₂O₃) nanoporous template. The de-doped states of the PPy nanowires were obtained from doped PPy nanowires through cyclic voltammetry (CV) using a solution of the catalyst in the BMIMPF₆ ionic liquid. We confirmed the de-doped states of PPy nanowires based on a decrease of the bipolaron peak of the ultraviolet and visible (UV–vis) absorbance spectra. The formation of PPy nanowires was visualized by using scanning electron microscopy and transmission electron microscopy. We studied the optical and structural properties of the doped and de-doped PPy nanowires by UV–vis absorbance and Fourier transform-infrared spectra. Our work included obtaining a laser confocal microscope Raman spectra for a single strand of the PPy nanowires.     

Preparation, characterization and the electrogenerated chemiluminescence behavior of WO3 nanocrystals

The (WO₃)_NCs/Nafion film electrode was prepared by immobilizing the synthesized WO₃ NCs on the surface of a glassy carbon electrode (GCE) with the help of Nafion. The ECL emission of the electrode in aqueous solution was affected by the buffer solution with respect to the pH and composition. And the strongest ECL was observed in an NH₃-NH₄Cl buffer with pH being 8.2. Only a weak ECL peak at 1.14 V which was originated from the annihilation process between oxidized and reduced species of WO₃ NCs was found. By adding coreactant triproplamine (TPrA) in buffer solution, an additional ECL peak at 1.13 V which was attributed to the electron-transfer reaction between the oxidized WO₃ NCs and reduced intermediate of TPrA was observed. The (WO₃)_NCs/Nafion film electrode exhibits excellent ECL property and good stability, which would promote the potential application of WO₃ NCs as a luminescence material for solid-state ECL detection.     

Electrodeposition of composite films consisting of polypyrrole and mesoporous silica

Electrochemical formation of composite films consisting of polypyrrole (PPy) and MCM particles has been presented, in which pyrrole is electrochemically oxidized in an aqueous solution with suspension of purely siliceous or aluminum-containing MCM-41. The composite films were characterized by scanning electron microscopy, X-ray diffraction and infrared reflection spectroscopy, and the electrochemical response of the PPy/MCM-deposited electrode to Fe(CN)₆³⁻ investigated. From IR spectra, it is indicated that the polymerization of pyrrole takes place on the internal wall of MCM particles where the cationic PPy is charge-balanced by the negatively charged MCM. A PPy/SiMCM composite electrode prepared in the presence of higher concentration of pyrrole (≧0.5 M) shows a reproducible electrochemical response for Fe(CN)₆³⁻. The CV curve on this electrode is comparable to that on pure PPy-modified electrode, and it is suggested that the negative charge on the mesopore surface is almost completely neutralized by the positive charge of PPy.     

Study of electronic‐ionic conducting transformation of temporarily protective oil coating in salt solution

In this paper, a multiple microelectrode array was developed to study the electronic‐ionic conducting transition of temporarily protective oil coating in salt solution. It was pointed out that there existed electronic‐ionic transition of temporarily protective oil coating in salt solution varying with immersion time. At the early stage of immersion, the oil coating was an electronic conductor, which having very low conductivity. With increasing of immersion time, the oil coating transformed from electronic conductor to ionic conductor, where ionic diffusion in the coating was predominant. Based upon Bailey and Ritchie's general electrochemical theory for the oxidation of metals, an electrochemical analysis of potential inhomogeneity of the oil coating was presented. It was assumed that only one step could be rate‐determining in the overall reaction in the metal/oil film/solution system. It was predicted that there were two kinds of film in the temporarily protective oil coating, ionic and electronic conducting film. For the ionic conducting film, potentials of oil coated electrode were equal to equilibrium potential of metal oxidation at the metal/coating interface (E_a^eq), and it had the most negative value. For the electronic conducting film, potentials obtained were equal to the equilibrium potential of the oxidant reduction at the coating/electrolyte interface (E_c^eq), and it had the most positive value. Potential measurements in this paper verified the results of Wormwell and Brasher's research in 1949; the distribution of potential on oil‐painted wire beam electrodes being heterogeneous and following a discontinuous binomial probability distribution were also elucidated.     

Erratum to “Mimicking photosynthesis: covalent [60]fullerene-based donor–acceptor ensembles” [Synth. Met. 147 (2004) 57–61]

Polypyrrole (PPy) nanowire modified electrode was prepared and its electrocatalytic behavior towards nitrate reduction was characterized_. The electrode surfaces were investigated by scanning electron microscopy (SEM) and energy-dispersive X-ray analysis (EDX). The electrocatalytic activity of modified graphite electrode was compared with graphite, copper (Cu) and platinum (Pt) electrode. The nitrite concentration produced at PPy modified electrode is lower than that at any other electrodes, and its changing tendency is opposite to any other electrodes. The PPy nanowire modified electrodes were further modified by electrodeposition of Cu. The results show that the produced nitrite concentration gets higher with the increase of Cu content. The primary experimental results show that the modified electrode has promise use in the remove of nitrate from water.     

Synthesis and redox behavior of PEDOT/PSS and PPy/DBS structures

Electrochemical synthesis of dodecylbenzenesulfonate (DBS⁻) doped polypyrrole (PPy/DBS) onto polystyrenesulphonate (PSS⁻) doped poly(3,4-ethylenedioxythiophene) (PEDOT/PSS) modified gold EQCM electrode was studied. Monitoring of mass and potential response during PPy growth onto PEDOT underlayer revealed at least three different stages in this process. AFM study confirmed that PEDOT film morphology constantly changed during the synthesis of PPy film onto its surface. Studying of redox properties of PEDOT/PSS + PPy/DBS structures showed that PEDOT influenced the redox processes of the structure after its complete coverage with PPy suggesting the formation of three-dimensional electrode.     

Facile decoration of polypyrrole nanoparticles onto graphene nanosheets for supercapacitors

A facile approach was developed to prepare the graphene nanosheets (GNS) supported polypyrrole (PPy) nanoparticles via the in situ chemical oxidative polymerization of pyrrole onto the surfaces of the GNS modified with sodium dodecyl sulfonate (SDS) as surfactant for GNS and dopant for PPy simultaneously. The morphologies of the graphene nanosheets supported polypyrrole nanoparticles (GNS/PPy nanocomposites) with different feeding ratios were characterized with transition electron microscopy (TEM). It indicated that the PPy nanoparticles had been successfully decorated onto the GNS surfaces. The electrochemical performances of the GNS/PPy nanocomposites were investigated with cyclic voltammetry (CV), constant current charge–discharge and electrochemical impedance spectroscopy (EIS) techniques. The nanocomposite exhibited specific capacitance of 294 F g⁻¹ at the charge–discharge current density of 10 mA cm⁻² in 1.0 M NaNO₃ electrolyte. It showed that the GNS/PPy nanocomposites might be promising electrode materials for supercapacitors.     

Electrochemical characterization of the different surface states formed in the corrosion of carbon steel in alkaline sour medium

In this study the different surface states that manifest in the corrosion process of 1018 carbon steel in alkaline sour environment, solution prepared specifically to mimic the sour waters occurring in the catalytic oil refinery plants of the Mexican Oil Company (PEMEX) (0.1 M (NH₄)₂S and 10 ppm NaCN at pH 9.2) were prepared and characterized. The surface states of the carbon steel were formed by treating the surface with cyclic voltammetry at different switching potentials (E_λ+), commencing at the corrosion potential (E_corr=−0.890 V vs sulfate saturated electrode, SSE). The surface states thus obtained were characterized using electrochemical impedance spectroscopy and scanning electron microscopy techniques. It was found that for E_λ+=−0.7 and −0.6 V vs SSE a first product of corrosion formed, characterized by a high passivity. Moreover, it was very compact (with a thickness of 0.047 μm). However, at more anodic potentials (E_λ+>−0.5 V vs SSE) a second corrosion product with non-protective properties (porous with a thickness of 0.4 μm and very active) was observed. The diffusion of atomic hydrogen (H⁰) was identified as the slowest step in the carbon steel corrosion process in the alkaline sour media. The H⁰ diffusion coefficients in the first and second products that formed at the carbon steel–sour medium interface were of the order of 10⁻¹⁵ and 10⁻¹² cm²/s respectively.     

Doping mechanism of PPy/LiDS film in aqueous solutions

We studied electrochemical redox reaction of polypyrrole (PPy) films prepared in an aqueous lithium dodecylsulfate (LiDS) solution by means of cyclic voltammetry, Auger electron spectroscopy, electrochemical quartz crystal microbalance and atomic force microscope, and presented a new doping–dedoping mechanism of PPy/LiDS film associated with the movement of DS⁻. During a potentiodynamic polymerization of PPy/LiDS, an additional small cathodic peak appeared at −0.37 V in addition to the main redox peaks at −0.81 V. PPy/LiDS film prepared under a galvanostatic condition also showed the additional cathodic peak, too. EQCM results indicated that the main redox peaks were due to the fast movement of small Li⁺ while the additional peaks were associated with the movement of DS⁻ despite of its large molecular size. In potentiostatic condition the movement of DS⁻ could be found even in negative potential region (−0.8 V) where the movement of Li⁺ is dominant for potentiodynamic condition. Thus, both cations and anions were involved in the redox process of PPy/LiDS film but the mobility of DS⁻ was controlled by scan rate of potential due to its bulkiness.     

Kinetic Parameters and Mechanism of Gold Electrooxidation in Thiocarbamide Solutions

Kinetics and mechanism of gold electrooxidation in sulfuric acid solutions of thiocarbamide (TCA) are studied by measuring voltammograms (VA) of gold and glassy carbon (GC) electrodes. In a potential (E) range from –0.2 to 1.2 V (SCE), VA of a gold electrode demonstrate three peaks. The first and the second peaks correspond to gold electrooxidation to [AuTCA_ads] + and [Au(TCA_ads)₃]³⁺ ions at E of 0.152 and 0.554 V, while the third one corresponds to TCA electrooxidation. The electrooxidation of TCA on GC electrodes is characterized by two VA peaks at 0.983 and 1.437 V. The first peak corresponds to the formation of formamidine disulfide (FADS) (k _a1 = 6.40 × 10^–4 cm/s), while the second peak corresponds to TCA oxidation to sulfides and hydrosulfides (k _a2 = 7.78 × 10^–5 cm/s). The composition of adsorption layers formed at the Au electrode is analyzed by Auger spectroscopy. The introduction of sodium sulfide into TCA solutions eliminates the formation of adsorption layers and accelerates Au oxidation in such solutions. The rate constants of gold electrooxidation k _a = 6.31 × 10^–3 cm/s and Au(I) electroreduction k _c = 5.46 × 10^–4 cm/s in TCA solutions are estimated. Kinetic parameters (charge transfer coefficients, reactions orders in carbamide) are determined and the mechanisms of Au and TCA oxidation in sulfuric acid solutions are proposed.__________Translated from Zashchita Metallov, Vol. 41, No. 3, 2005, pp. 316–325.Original Russian Text Copyright © 2005 by Kozin, Kozina, Bogdanova.     

Preparation of a one-dimensional polymer film on passivated iron by modification of a carboxylate ion self-assembled monolayer with octyltriethoxysilane for preventing passive film breakdown

A self-assembled monolayer (SAM) of 16-hydroxyhexadecanoate ion HO(CH₂)₁₅CO₂⁻(HOC₁₆A⁻) has been prepared on an iron electrode passivated in a borate buffer solution (pH 8.49) in the preceding paper. In this work, the HOC₁₆A⁻ SAM on the passivated electrode was modified with octyltriethoxysilane C₈H₁₇Si(OC₂H₅)₃ to form a film composed of one-dimensional polymer. Prevention of passive film breakdown was examined by anodic polarization measurements of the electrodes uncoated and coated with the modified SAM in the borate buffer containing 0.1 M of Cl⁻. The pitting potential, E_pit of the coated electrode shifted from that of the uncoated electrode in the positive direction, indicating prevention of passive film breakdown. The anodic current density was decreased in the passive and transpassive regions by coverage with the modified SAM. Neither current spikes nor E_pit was observed in the curve of the passive region in some cases, demonstrating complete protection of the passive film against breakdown in the Cl⁻ solution. The modified SAM on the electrode was characterized by X-ray photoelectron and FTIR reflection spectroscopies and contact angle measurement.     

Effect of polystyrenesulphonate and electrolyte concentration for electrical properties of polypyrrole film on aluminium alloy using conductive AFM

The electrochemical synthesis of polystyrenesulphonate (PSS) doped polypyrrole (PPy) film onto aluminium alloy (AA 2024-T3) under galvanostatic conditions at current densities of 1 mA cm^?2 was studied. In this study, conductive atomic force microscopy (C-AFM) was performed to investigate the electrical properties of PPy film on AA 2024-T3 depending on the concentration of PSS as dopant and nitric acid as electrolyte during electrochemical synthesis. The addition of HNO₃ to aqueous electrolyte solution is found to allow the electrochemical synthesis of well adhering homogeneous PPy film in the presence of PSS on AA 2023-T3. The PPy film in the presence of nitric acid alone can be synthesised, although this film showed the poor quality of the electrical properties of PPy film. According to C-AFM, the study confirmed that the conductivity of PPy film is significantly increased with increasing the PSS, nitric acid concentration and electrochemical deposition time.