New single-step electrosynthesis process of homogeneous and strongly adherent polypyrrole films on iron electrodes in aqueous medium

Homogeneous and strongly adherent polypyrrole (PPy) films were electrochemically synthesized on iron electrodes in sodium tartrate (Na₂C₄O₆H₄ 0.2 M) aqueous solution. This one step pyrrole electropolymerization process has been successfully achieved under different electrochemical techniques, such as potentiodynamic, galvanostatic and potentiostatic modes. During the first stage of the electrochemical process the tartrate counterion slows down the iron dissolution by leading to the formation of a passivation layer on the working electrode surface, and the pyrrole electropolymerization takes place. The electrosynthesized polymer deposit has been characterized by several microscopic and spectroscopic techniques. Any iron traces have been detected by X-ray photoelectron spectroscopy (XPS) on the outer side of the PPy films, which confirms the compactness and the homogeneity of the polymeric coating. Scanning electronic microscopy (SEM) imaging showed uniform and compact PPy coatings with cauliflower-like structure. Infra-red (IR) and Raman spectroscopies proved that the obtained PPy films have the same vibrational properties as those electrodeposited on noble Pt plates.     

Optimization of electrochemical polymerization parameters of polypyrrole on Mg–Al alloy (AZ91D) electrodes and corrosion performance

We report on the optimum electropolymerization conditions of polypyrrole (PPy) coatings on Mg alloy AZ91D electrodes from aqueous electrolytes of sodium salicylate via cyclic voltammetry (CV). Results show that initial and end potential values during the electrochemical coating procedure play an important role on the adhesion and corrosion performance of PPy films. Corrosion tests of AZ91D electrodes coated with PPy under optimized conditions show a good corrosion performance during 10 days in Na₂SO_4, without peeling off of these thin films.     

Effect of the surface roughness of conducting polypyrrole thin-film electrodes on the electrocatalytic reduction of nitrobenzene

Conducting polypyrrole (PPy) thin-film electrodes were prepared by the electropolymerization of pyrrole on gold-coated glass plates. Films of various roughnesses were obtained by the variation of the scan rates during electropolymerization. These thin films were modified by doping with 6mM of the dopant NiCl₂. The surface morphology of the films was studied by scanning electron microscopy and atomic force microscopy (AFM), which suggested films prepared with a high scan rate were rougher in nature than the films produced with a low scan rate. The electrocatalytic reduction of nitrobenzene was carried out with these electrodes with the cyclic voltammetry technique in acetonitrile containing 0.1M HClO₄ as a supporting electrolyte. The various results obtained show that the conducting PPy thin-film electrodes were catalytically active toward the electroreduction process. The modified PPy film electrodes doped with NiCl₂ were more active toward nitrobenzene electroreduction than the PPy film alone. The results indicate that the roughness of the films played a very important role in determining their catalytic activity. The PPy films that were more rough in nature were catalytically more active than the smooth films; this may have been due to the availability of more reactive sites in the case of rough films. The apparent diffusion coefficients of the PPy film electrodes were also calculated. © 2012 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

Electrochemical synthesis of polypyrrole (PPy) and PPyǀmetal composites on copper electrode and investigation of their anticorrosive properties

This study reports corrosion protection behaviour of various metal cations electrodeposited onto polypyrrole (PPy) coated copper (Cu) electrode. Before electropolymerization of pyrrole, the Cu electrode was passivated in 0.1 M oxalic acid via cyclic voltammetry method. After the coating process, metal cation electrodeposition onto PPy coating was carried out in 10⁻² M CuCl₂, ZnCl₂, FeCl₂ and NiCl₂ solutions. Corrosion behaviour of uncoated, PPy and PPy|metal coated Cu electrodes was studied in 0.1 M H₂SO₄ solution by using potentiodynamic polarization, chronoamperometric and impedance spectroscopic measurements. Surface morphologies were examined by scanning electron microscope (SEM). All the electrochemical measurements were in good agreement showing that metal electrodeposited PPy coated Cu electrodes have a higher corrosion resistance. Furthermore, SEM results show that while all the samples have a homogeneous distribution of metal cations, zinc and nickel have a much better homogeneous distribution compared to copper and iron. It was found that the best corrosion protection is provided by PPy|Zn and PPy|Ni coatings and there is a significant increase in their polarization resistance with increasing amounts of electrodeposited cations.     

Zinc hexacyanoferrate film as an effective protecting layer in two-step and one-step electropolymerization of pyrrole on zinc substrate

The two-step and one-step electrosynthesis processes of polypyrrole (PPy) films on the zinc substrate are described. The two-step process includes (i) the zinc surface pretreatment with hexacyanoferrate ion in the aqueous medium in order to form a zinc hexacyanoferrate (ZnHCF) film non-blocking passive layer on the surface and with the view to prevent its reactivity and (ii) electropolymerization of pyrrole on the ZnHCF|Zn-modified electrode in aqueous pyrrole solution. In this context, both the non-electrolytic and electrolytic procedures were adapted, and the effect of some experimental conditions such as supporting electrolyte, pH and temperature of the solution at the zinc surface pretreatment step as well as pyrrole concentration and electrochemical techniques at the polymerization step was investigated. By optimizing the experimental conditions in both steps, we have obtained a homogeneous and strongly adherent PPy films on the zinc substrate.The one-step process is based on the use of an aqueous medium containing Fe(CN)₆⁴⁻ and pyrrole. The ferrocyanide ion passivates the substrate by formation of ZnHCF film during the electropolymerization process of pyrrole and therefore makes it possible to obtain strongly adherent PPy films, with controlled thickness, either by cyclic voltammetry or by electrolysis at constant current or constant potential without any previously treatment of the zinc electrode surface. The polypyrrole films deposited on the zinc electrode were characterized by cyclic voltammetry and scanning electron microscopic (SEM) measurement.     

Improvement of polypyrrole films for corrosion protection of zinc-coated AZ91D alloy

To improve the protection against the corrosion of AZ91D magnesium alloy provided by conducting polypyrrole (PPy) films, optimization of the electrochemical synthesis of the PPy film was investigated. The bi-layered PPy film was prepared under constant current control, first in a sodium tartrate solution containing molybdate and second in a sodium dodecylsulfate (DS) solution (after the AZ91D alloy was covered by zinc electroplating). Corrosion testing of the zinc-coated AZ91D alloy covered with the PPy film was performed in 3.5% NaCl solution. The more protective PPy film doped with tartrate ions (PPy-Tart film) was formed by the lower current density (CD). Doping of molybdate ions (MoO₄²⁻) into the PPy-Tart film significantly improved its corrosion protection properties. When the PPy-Tart-MoO₄ layer was covered by an outer PPy layer doped with DS ions, the corrosion protection was further improved. The imposition of ultrasonic waves during the electropolymerization of the inner PPy-Tart-MoO₄ layer was effective in the improvement of corrosion protection. The bi-layered PPy-Tart-MoO₄/PPy-DS film prepared under ultrasonic irradiation maintained the zinc-coated AZ91D alloy in the passive state during the corrosion test in NaCl solution for 221 h, during which no corrosion products appeared.     

Electrodeposition of polypyrrole layers on aluminium from aqueous electrolytes

A screening of twenty aqueous electrolytes for a film-forming electropolymerization of pyrrole with Al was performed. Electrodeposition of well adhering homogeneous polypyrrole layers on aluminium is possible from aqueous electrolytes containing 0.1–0.8M oxalic acid. Pretreatment of the metal by polishing (PD) or by anodic (galvanostatic) activation (GA) is an essential step. In all cases, the Al₂O₃ surface layer with pores, usually filled with electrolyte, is transformed to a Al₂O₃ layer with polypyrrole filled pores. The PPy-layers on Al allow an easy cathodic coating with metals like copper. The hydrogenoxalate doped layers exhibit the ususal redox capacity,y=0.3. The sandwich structure Al/Al₂O₃/PPy represents a condenser with an unusual composite dielectric with the electronically conducting plates Al and PPy. According to our impedance measurements, the PPyin the pores is a high resistivity material due to overoxidation in the course of electropolymerization at high local current densities. The composite, Al₂O₃/overoxidized PPy, exhibits an unusually high permittivity, in the order of 10³.     

The morphology and conductivity of polypyrrole/polyurethane alloy films

Polymeric composites with conductivities ranging from 10^–4 to 1 S cm^–1 were prepared by electrochemically polymerizing pyrrole in a matrix of polyurethane. The polypyrrole/polyurethane alloy films obtained were characterized by element analysis, electron microscopy and electrical conductivity measurements. The morphology of the films depended on the solvent, the electrolyte and the current density. The mechanism of the electrochemical polymerization showed that PPy grew in a treelike structure, with molecular chains extending from the electrode surface into the solution. The transition temperature of the PPy/PU increased with the PPy content.     

Copper/polypyrrole multilayer coating for 7075 aluminum alloy protection

The corrosion behavior of 7075 aluminum (Al), copper modified Al (Al/Cu), polypyrrole modified Al (Al/PPy) and copper (under layer)/polypyrrole (top layer) modified Al (Al/Cu/PPy) samples were investigated in 3.5% NaCl solution. The copper plating on aluminum was carried out from acidic copper sulphate solution by electroless method. Polypyrrole (PPy) was electrochemically synthesized on Al and Al/Cu electrodes from 0.1 M pyrrole containing 0.4 M oxalic acid solution using cyclic voltammetry technique. The films synthesized were characterized by Fourier transform infrared spectroscopy (FT-IR). The thermal stability of PPy films was investigated by thermogravimetric analysis (TGA). The surface morphologies were examined by scanning electron microscopy (SEM) and atomic force microscopy (AFM). The corrosion behavior of samples was investigated by electrochemical impedance spectroscopy (EIS) and anodic polarization curves. The data obtained showed that the synthesis of PPy on top of the Cu layer significantly enhances the corrosion resistance of Al by exhibiting a barrier effect against the attack of corrosive environment.     

Sweet aqueous solution for electrochemical synthesis of polypyrrole part 1B: On copper and its alloys

The electrochemical synthesis of polypyrrole (PPy) on copper and brass has been successfully achieved in sodium saccharinate and pyrrole aqueous medium. The synthesized coating under several electrochemical techniques such as cyclic voltammetry, galvanostatic and potentiostatic is homogeneous and adherent. PPy has been characterized by SEM, XPS, IR and Raman spectroscopy and its quality has been confirmed. The doping level obtained from N 1s XPS signal of the oxidized PPy depends on the electrochemical technique used to produce the film. The corrosion performance of PPy/copper and PPy/brass has been evaluated in 3% NaCl and 0.1 M HCl using linear polarization and electrochemical impedance spectroscopy. The results show that PPy coating electrodeposited from sodium saccharinate exhibits significant corrosion protection properties.     

Polymers and copolymers of pyrrole and thiophene as electrodes in lithium cells

The performance of pyrrole and thiophene polymer electrodes in lithium cells has been examined in the lithium perchlorate–propylene carbonate electrolyte by cyclic voltammetry. Polypyrrole films were synthesized in 'wet' and 'dry' conditions; pyrrole and thiophene copolymers were prepared at different potentials and bilayers were prepared by sequential deposition of polythiophene (PTh) and polypyrrole (PPy) films. The polymers were cycled between 2.0V and 4.0V in the lithium cells. The effects of disconnecting the electrodes from the cell on the behaviour of the polymers regarding doping and coulombic efficiency were also studied. The cycling performance of the 'wet' PPy is better than 'dry' PPy, bilayer PTh/PPy and copolymers. No mixed behaviour was observed for a bilayer where the inner layer was polythiophene and the outer layer was polypyrrol with a thickness PPy/Pth ratio equal to ten. The copolymer prepared at 3.9V vs Li/Li+ showed the higher energy capacity in Whkg–1 calculated from the anodic charge.     

Simple and rapid synthesis of NiO/PPy thin films with improved electrochromic performance

Nickel oxide/polypyrrole (NiO/PPy) thin films were deposited by a two step process in which the NiO layer was electrodeposited potentiostatically from an aqueous solution of NiCl₂·6H₂O at pH 7.5 on fluorine doped tin oxide (FTO) coated conducting glass substrates, followed by the deposition of polypyrrole (PPy) thin films by chemical bath deposition (CBD) from pyrrole mixed with ammonium persulfate (APS). The NiO/PPy films were further characterized for their structural, optical, morphological and electrochromic properties. X-ray diffraction study indicates that the films composed of polycrystalline NiO and amorphous PPy. Infrared transmission spectrum reveals chemical bonding between NiO and PPy. Rectangular faceted grains were observed from scanning electron microscopy results. The electrochromic (EC) property of the film was studied using cyclic voltammogram (CV), chronoamperometry (CA) and optical modulation. The NiO/PPy presents superior EC properties than their individual counterparts. The coloration/bleaching kinetics (response time of few ms) and coloration efficiency (358 cm²/C) were found to be improved appreciably. The dramatic improvement in electrochemical stability (from about 500 c/b cycles for PPy to 10,000 c/b cycles for NiO/PPy) was observed. This work therefore demonstrates a cost-effective and simple way of depositing highly efficient, faster and stable NiO/PPy electrodes for EC devices.     

Evaluation of corrosion resistance of polypyrrole/functionalized multi-walled carbon nanotubes composite coatings on 60Cu–40Zn brass alloy

Polypyrrole/multi-walled carbon nanotubes (PPy/MWCNT) and its carboxylic functionalized (PPy/MWCNT-COO⁻) composite films were successfully electropolymerized by cyclic voltammetry as protective coating against corrosion on 60Cu–40Zn brass alloy surface. It yielded to strongly adherent and smooth nanocomposite films. Kinetics of the corrosion protection was investigated in 3.5 wt% NaCl solutions by electrochemical impedance spectroscopy (EIS) and potentiodynamic polarization tests. The results showed that the presence of MWCNT in PPy coat considerably reduces the corrosion rate of 60Cu–40Zn brass alloy. The enhanced inhibition is most likely due to interaction between MWCNT and PPy. This in turn, improves the alloy passivation improvement and alters the permselectivity of the coating from anionic selectivity to the cationic selectivity. Moreover, PPy/MWCNT-COO⁻ functionalized nanocomposite provided higher corrosion resistance coating than PPy/MWCNT alone.     

Preparation, structure and electrochemistry of a polypyrrole hybrid film with [Pd(dmit)2], bis(1,3-dithiole-2-thione-4,5-dithiolate)palladate(II)

The synthesis of a hybrid material obtained by electropolymerization of a solution of pyrrole and [NEt₄]₂[Pd(dmit)₂] (1,3-dithiole-2-thione-4,5-dithiolate, [dmit]²⁻, [C₃S₅]²⁻) in acetonitrile solution is reported. FTIR and UV-vis spectroscopy showed that the [Pd(dmit)₂]²⁻ anion had been inserted in the polypyrrole framework without modification during the electropolymerization process. Cyclic voltammetry showed that the material has electroactivity undergoing redox processes related to the conducting polymer and the counteranion. The electrochemical results also suggest that the counteranion is not trapped in the PPy matrix undergoing anion exchange during the redox cycle of PPy. The PPy/[Pd(dmit)₂]²⁻ exhibits good thermal stability and has a higher intrinsic conductivity value (4.27 × 10⁻³ S cm⁻¹) than do other PPy/dmit films previously studied.     

The actuation behavior and stability of p‐toluene sulfonate doped polypyrrole films formed at different deposition current densities

Free‐standing films of polypyrrole doped with p‐toluene sulfonate (PPy/pTS) were electropolymerized galvanostatically at different deposition current densities and their electrochemomechanical deformation (ECMD) properties were measured in situ during cyclic voltammetry experiments. It was found that films exhibiting a higher cation‐driven actuation strain were generated when a lower current density was used in electropolymerization, which also led to an increase in PPy conductivity and doping level. A decrease in cation‐driven strain with time was observed in all cases due to a loss of pTS anions from the films. Raman, FTIR, and elemental analyses were used to characterize the films grown at different deposition current densities and no sign of excessive overoxidation was found. SEM images revealed that the morphology of the films was affected by the current density during electropolymerization. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Copper and brass aged at open circuit potential in slightly alkaline solutions

Surface oxide films were grown on 99.99% copper and brass (copper–zinc alloy, Cu77Zn21Al2) in 0.1 mol L⁻¹ borax solution at open circuit potential and were characterized using various experimental techniques. The composition of the passive films formed in situ on the different materials was studied using differential reflectance spectroscopy. The thickness of the oxide layers on copper and brass was compared by chronopotentiometric curves and potentiodynamic reductions. The electrical properties of each oxide were analyzed by means of electrochemical impedance spectroscopy. Their influence on the oxygen reduction reaction was also investigated using voltammetry hydrodynamic tools such as the rotating disk electrode. The results show that the incorporation of Zn to Cu in brass changes the composition and the thickness of the surface film. The films grown on brass tend to be thicker but less resistive and Zn compounds incorporate to the film. This is supported by results from reflectance and impedance spectroscopy. The kinetics of oxygen reduction is strongly inhibited on oxidized electrodes, particularly in the case of brass. The global number of exchanged electrons remains close to four and seems to be independent of the presence of surface oxides.     

Preparation and properties of transparent and conducting nylon 6-based composite films

Highly transparent and conducting polypyrrole–(PPy–N) and polyaniline–nylon 6 (PAN) composite films could be easily obtained by immersing nylon 6 films containing pyrrole or aniline into an oxidant solution such as aqueous FeCl₃ solution or aqueous (NH₄)₂S₂O₈ solution containing HCl. The conductivity, transmittance, and mechanical properties of these composite films were affected by the preparative conditions. The maximum conductivity and transmittance of the PPy–N composite films were 10^?3 S/cm and about 75% at 550 nm, and in the case of the PA–N composite films, 10^?2 S/cm and 75%, respectively. The morphology of PPy–N and PA–N composite films depended on the polymerization conditions, which might be due to the difference in the polymerization speed of pyrrole or aniline in polymer matrices. These PPy–N and PA–N composite films exhibited good environmental stability and excellent mechanical properties. © 1994 John Wiley & Sons, Inc.     

Electrodeposition and characterization of polypyrrole films on aluminium alloy 6061-T6

Polypyrrole films on aluminium alloy 6061-T6 were prepared by electropolymerization of pyrrole in sulphuric acid using two different processes - cyclic voltammetry and potentiostatic polarization - and assessed through SEM observation and voltammetry. The anticorrosive properties of these films were studied by polarization curves and electrochemical impedance spectroscopy.The polypyrrole films formed by both methods are homogeneous and present a globular structure. However, it was found that the films produced by cyclic voltammetry are thicker than those produced potentiostatically at a potential equal to the upper limit of the cyclic voltammetry (E_λa). It was also found that there is an optimum value for the formation potential (E_appl, in the case of the potentiostatic method or E_λa for cyclic voltammetry). Above this value, overoxidation of the polymer occurs, which is found to be deleterious to the coated system behaviour.From polarization curves no major differences were detected between the PPy-coated alloy and the bare material, indicating that no significant protection is achieved by the polymer coating. On the other hand, Bode diagrams are typical of a system undergoing pitting corrosion and show lower impedance values for the alloy covered with polypyrrole than for the bare metal. This can be attributed to the conductive character of the polypyrrole films.     

Investigation by EQCM of the electrosynthesis and the properties of polypyrrole films doped with sulphate ions and/or a Keggin-type heteropolyanion, SiMo12O40

The first part of this paper describes in detail the electrochemical synthesis of polypyrrole (PPy) films monitored by electrochemical quartz crystal microbalance (EQCM). These films are either doped only with a Keggin-type heteropolyanion (HPA), SiMo₁₂O₄₀⁴⁻, or co-doped with such polyanions and sulphate ions. It is evidenced that this HPA catalyses the electropolymerisation of the pyrrole since it is able to oxide pyrrole monomer, and on the other hand, that HPAs are definitively entrapped into the polypyrrole film as shown by their electrochemical response. All the PPy film is electroactive. When the co-doped film is obtained by potentiodynamic method, its anion composition is not homogeneous in depth, there is a concentration gradient of the doping anions. In the second part of this paper, the morphology of the films is shown as well as their electrochemical characterisations that were carried out by EQCM in order to focus on the charge compensation process that occurs during SiMo₁₂ reduction and re-oxidation. In a wide domain of potentials, only the HPA response is observed, the polymer remains in its conducting form. The SiMo₁₂O₄₀⁴⁻ doped PPy films are cationic films. When several types of cations are present in the medium, the influence of the pH on the nature of the cations implied in the charge compensation that occurs during SiMo₁₂ reduction and re-oxidation is important. When the PPy film is co-doped, it is possible to obtain a mixed PPy film. Another important finding is the stability of trapped SiMo₁₂ ions in contact with solutions of pH higher than 4, on the contrary to what occurs when they are in solution.     

Electrodeposition and Capacitive Behavior of Films for Electrodes of Electrochemical Supercapacitors

Polypyrrole films were deposited by anodic electropolymerization on stainless steel substrates from aqueous pyrrole solutions containing sodium salicylate and tiron additives. The deposition yield was studied under galvanostatic conditions. The amount of the deposited material was varied by the variation of deposition time at a constant current density. SEM studies showed the formation of porous films with thicknesses in the range of 0–3 μm. Cyclic voltammetry data for the films tested in 0.5 M Na₂SO₄ solutions showed capacitive behavior and high specific capacitance (SC) in a voltage window of 0.9 V. The films prepared from pyrrole solutions containing tiron showed better capacitive behavior compared to the films prepared from the solutions containing sodium salicylate. A highest SC of 254 F g⁻¹ was observed for the sample with a specific mass of 89 μg cm⁻² at a scan rate of 2 mV s⁻¹. The SC decreased with an increasing film thickness and scan rate. The results indicated that the polypyrrole films deposited on the stainless steel substrates by anodic electropolymerization can be used as electrodes for electrochemical supercapacitors (ES).