An EQCM study of the deposition and doping/dedoping behavior of polypyrrole from phosphoric acid solutions

The potentiostatic deposition of polypyrrole (PPy) from 0.1 M aqueous phosphoric acid solution and the doping/dedoping behavior of the resulting films have been investigated by the electrochemical quartz crystal microbalance (EQCM) technique. The change of the complex shear modulus during the film growth and during the doping/dedoping were calculated using the acoustic impedance method. It was found that the films contain only ca. 1 wt% water in the oxidized state which is in accordance with their relatively high storage modulus of 38 MPa and low loss tangent of 0.05. Comparing H₃PO₄ (pH 1) and NaH₂PO₄ (pH 8) it was found that the doping/dedoping in the latter is accompanied by a strong increase of the surface roughness which is a direct result of cation exchange present at pH 8.     

聚吡咯/硫化镉的制备及其光学性能研究

将聚吡咯和纳米粒子结合起来制备的复合材料兼具了导电高分子材料、无机半导体材料的优势,与此同时这种的复合材料还具有显著的三阶非线性光学性质。本文拟采用界面氧化聚合法制备聚吡咯膜,通过实验发现反应的最佳溶剂为三氯甲烷,最佳的氧化剂为过硫酸铵。当聚吡咯于过硫酸铵反应浓度均为0.15 mol/L左右时可以生成表面平整、厚度适中、力学性能较好的聚吡咯膜。通过将上述方法制备的聚吡咯膜先浸泡在醋酸镉溶液中吸附Cd2+,最后与硫代乙酰胺处理得到PPy/CdS复合材料。本实验采用了探针式表面轮廓仪分析、扫描电镜(SEM)、傅立叶红外光谱(FTIR)、X-射线衍射(XRD)、Z-扫描测试法、热重(TG)分析等对产物进行表征。结果表明,聚吡咯/硫化镉纳米复合材料上纳米粒子的分布状况及粒子大小与掺比浓度有关,浓度越低分布越密、粒子直径越小,当聚吡咯、硫化镉的掺杂比达到1:0.001时粒子直径可达20 nm左右。此外,复合了硫化镉纳米粒子后聚吡咯的热稳定性提高了33.3%。由Z-扫描结果显示PPy/CdS具有很强的三阶非线性特性。     

Two reduction processes of conducting polypyrrole tosylate film in aqueous solutions

The electrochemical properties of polypyrrole tosylate [PPy(TsO⁻)] in aqueous solutions were investigated by cyclic voltammetry and ac impedance measurements. The cyclic voltammograms (CVs) of PPy(TsO⁻) show two reduction processes. Two doping sites of the counteranions in PPy(TsO⁻), site A with the counteranions located between the PPy layers and site B with the counteranions located in the PPy layers, were proposed based on the results of the electrochemical studies, and the partial counteranion exchange occurred when PPy(TsO⁻) was dipped in a 1 mol/L HNO₃ aqueous solution. The reduction of site A is accompanied by the dedoping of counteranions and the reduction of site B is carried out with the insertion of solution cations. The electrochemical kinetics of the redox processes of site A was analyzed based on the ac impedance results. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 79: 350–355, 2001     

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     

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.     

Electrosynthesized molecularly imprinted polypyrrole films for enantioselective recognition of l-aspartic acid

The electrosynthesis, overoxidation and characterization of l-aspartic acid (l-Asp) imprinted polypyrrole (PPy) films have been performed by using electrochemical quartz crystal microbalance (EQCM). Following the determination of the optimal electrosynthesis parameters for the formation of a smooth and uniform PPy/l-Asp films, the overoxidized polypyrrole (oPPy) matrix templated with either l- or d-aspartic acid (l-, d-Asp) was evaluated as a potential enantioselective recognition element. Under potentiodynamic conditions and in strongly acidic media a significantly higher sensitivity of the l-Asp acid imprinted overoxidized polypyrrole film (oPPy/l-Asp) for l-Asp than d-Asp was observed. The results suggest the feasibility of preparing molecularly imprinted films by electropolymerization for the enantioselective recognition of amino acids and the suitability of EQCM for both monitoring the selective recognition as well as to electrochemically modulate the binding process.     

The effect of polypyrrole-bound anthraquinonedisulphonate dianion on cathodic reduction of oxygen

Functionalized polypyrrole (PPy) films were prepared by incorporation of anthraquinonedisulphonate (AQDS) as doping anion during the electropolymerization of pyrrole (Py) monomer at a glassy carbon electrode from aqueous solution. The electrochemical behavior of the PPy-bound AQDS modified electrode and cathodic reduction of oxygen on the resulting polymer film were studied. An obvious surface redox reaction corresponding to AQ/H₂AQ was observed and the dependence of this reaction on the solution pH was also illustrated. The electrocatalytic ability of the PPy-bound AQDS modified electrode was demonstrated by the electroreduction of oxygen at the optimized pH of 6.3 in a phosphate buffer. The reduced AQDS (H₂AQ) is responsible for the extraordinary catalytic activity to the oxygen reduction reaction. The PPy layers not only act as an electron mediator, but also facilitate the stability of the modified electrode. It was found that the catalytic reaction occurred in the presence of the bound AQDS and O₂ is in agreement with an electrochemical–chemical (EC) mechanism. The kinetic parameters of oxygen reduction were determined using Koutecky–Levich equation and Tafel polarization technique.     

Investigations of electrochemical polymerization processes of thin poly(pyrrole) films and its application to anion sensor based on surface plasmon resonance

A study of the response behavior of anion to surface plasmon resonance (SPR) based sensor, in which a Poly(pyrrole) (Ppy) modified thin gold film was used as a sensor chip is described. In situ surface plasmon resonance and electrochemical methods were used to investigate the electropolymerization and doping/dedoping processes of thin Ppy film. The electropolymerization of pyrrole was carried out under cyclic voltammetric conditions, and simultaneously monitored by in situ SPR. It has revealed that the transition between the reduced state and oxidized state of the Ppy, corresponding to the doping/dedoping of anions, can lead to very distinct changes in SPR signal at a fixed angle of incident laser beam. Furthermore, it has demonstrated that the concentration, the charge and size of anions, as well as the film thickness play important roles in the ingress/egress process of anions. Based on this, this combination of experimental approaches can be used to detect Cl⁻. SPR signal exhibited a good linear relationship with the concentration of Cl⁻.     

One-step preparation of poly(NIPAM-pyrrole) electroconductive composite hydrogel and its dielectric properties

Conductive polymers and hydrogels are two of the hot prospect polymer types that are used for new stimuli responsive materials. In this study, one-step preparation of electroconductive composite hydrogels containing polypyrrole (PPy) and N-isopropylacrylamide (NIPAM) using free radical polymerization technique was achieved with N,N-methylenebisacrylamide as a crosslinker and ammonium peroxy disulphate (APS) as initiator, in mixture of water/isopropyl alcohol. The equilibrium swelling degree of the poly(NIPAM)-pyrrole) electroconductive composite hydrogel was 9.88 g of H₂O/g dry polymer. According to TGA results, the thermal stability of the prepared composite poly(NIPAM-PPy) conductive hydrogel (700°C) hydrogel is higher than that of pure poly(NIPAM) hydrogel (600°C). Furthermore, prepared samples were characterized by FTIR, and SEM analyzes. Later, the samples were pressured into pellets so that electrical impedance spectroscopy (EIS) measurements were taken between 10 and 10 MHz at room temperature. The dielectric constant value of composite poly(NIPAM-PPy) hydrogel at 10 Hz is almost 10 times higher than that of poly(NIPAM) hydrogel. Both samples' real and imaginary parts of dielectric constant decreased with increased frequency. Samples exhibited non-Debye relaxation since experimental data fit into dielectric model of Havriliak-Negami. Moreover, low frequency data yielded d.c. conductivity of the pure and composite samples as 3.74 × 10⁻¹¹ and 1.02 × 10⁻⁸ S/cm, respectively. Real part of impedance at low frequencies also points out ~10³ times lower resistance values at 10 Hz for composite poly(NIPAM-PPy) hydrogel. Therefore, EIS results support that electroconductive composite hydrogel fabrication was achieved using free radical polymerization technique.     

The influence of dopant permeability on electrochromic performance of polypyrrole films

Detailed characteristics of the electrochromic performance of polypyrrole films under electrochemical doping and dedoping are studied. The response time for colour change in polypyrrole films depends on the dopant permeability. The change in film colour occurring in the redox reaction of the film is investigated in detail as a function of the dopant electrolyte solution and the thickness of the polypyrrole film. Three colour states for polypyrrole films are demonstrated: yellow green, dark brown, and blue.     

Structural and mechanical degradation of polypyrrole films due to aqueous media and heat treatment and the subsequent redoping characteristics

Polypyrrole films doped with p-toluenesulfonate and poly(4-styrenesulfonate) anions were synthesized electrochemically. These films were treated with water and dilute NaOH solution for varying periods of time. The films do not lose the anions readily when treated with water. In NaOH, dedoping occurs rapidly, either via migration of the toluenesulfonate anions out of the film or the neutralization of the poly(4-styrenesulfonate) anions. The undoped polypyrrole is very susceptible to ring oxidation resulting in C(SINGLE BOND)O and C(DOUBLE BOND)O groups. Severe deterioration of the mechanical properties of the film also results upon prolonged exposure to NaOH. The effects of heat on the polypyrrole doping level, structure, and mechanical properties were investigated. The results from redoping experiments suggest that unless the dedoping process by NaOH is carried out rapidly, the redoped films will have significantly lower doping levels and conductivities than the pristine films © 1997 John Wiley & Sons, Inc. J Appl Polym Sci 64: 519–526, 1997     

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     

Tailoring the optical properties of PVA/PVP blend by doping with Cu/MnS nanoparticles

PVA/PVP blend embedded with different ratios of nano Cu_0.9Mn_0.1S (Cu/MnS) was prepared with thermolysis and casting techniques. X-ray diffraction analysis showed the formation of nano Cu/MnS as a single hexagonal phase with an average crystallite size 11 nm. Scanning electron microscope (SEM) revealed nearly homogenous particles morphology. Fourier transform infrared (FTIR) spectroscopy technique was applied to characterize the Cu/MnS doped PVA/PVP matrix. UV measurements were utilized to investigate the optical properties in detail. Upon doping with Cu/MnS, the bandgap of PVA/PVP was significantly decreasing with the amount of doping; which enabling tailoring the band gap depending on the doping content. The analysis showed that the main possible transitions in pure PVA/PVP blend are indirect allowed and direct forbidden. On the other hand, for the doped blend samples, the direct allowed is the main possible transition. Moreover, the refractive index and the real and imaginary parts of the dielectric constant increased upon increasing the Cu/MnS amount doped.     

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.     

The role of ion and solvent transport during the redox process of conducting polymers

The understanding of the redox behavior of conducting polymers is essential for a successful application of these so-called synthetic metals as functional coatings. The redox process involves the exchange of ions and solvent molecules. This so called doping/dedoping process involves changes of the mechanical and the electronic structure of the polymer. This paper discusses investigations at poly(3,4-ethylenedioxythiophene (PEDOT) and poly(pyrrole) (Ppy) by the electrochemical quartz crystal microbalance (EQCM) technique and electrochemical impedance spectroscopy (EIS). In the case of PEDOT a determination of the anion and the solvent fluxes was possible, and it was found that most anions replace solvent molecules upon their incorporation. The doping/dedoping mechanism of Ppy is more complicated. Here, the first redox cycles are characterized by a complex interplay of cation, anion and solvent fluxes with irreversible changes of the polymer structure. However, in combination with EIS new insights of the ion and solvent exchange and its influence on the electronic properties can be achieved.     

Development of supercapacitor active composites by electrochemical deposition of polypyrrole on carbon nanofibres

In this study, pyrrole monomer is polymerized on carbon nanofibres (CNFs) via electropolymerization. This is a new technique to produce a chemically bonded CNF–polypyrrole composite. Deposition of the polypyrrole (PPy) on the nanofibres was optimized by varying the degree of deposition and deposition speed. Optimization studies have proven that the high deposition amounts result in blocks of polymers, which can be overcome through tuning the degree of polymerization by means number of cycles of electropolymerization and the scan rate of the electropolymerization.     

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.     

The corrosion-inhibiting effect of polypyrrole films doped with p-toluene-sulfonate,benzene-sulfonate or dodecyl-sulfate anions,as coating on stainless steel in NaCl aqueous solutions

This article presents a study of the conditions for electro-synthesis of polypyrrole (PPy) films on stainless steel, in the presence of the anions p-toluene-sulfonate (pTS), benzene-sulfonate (BS) or dodecyl-sulfate (DS). Cyclic voltammetry (CV) was used in the synthesis of the polypyrrole films on the stainless steel (SS). These polymeric films were characterized by IR and UV–vis spectroscopy and their morphology and thickness were analyzed by scanning electron microscopy (SEM). Their performance as protective films against corrosive processes presented by the SS/PPy-pTS, SS/PPy-BS or SS/PPy-DS systems was evaluated in 0.1 M NaCl aqueous solution. The study of the corrosion processes of the stainless steel/polymer systems was conducted through measurements of open circuit potential (E_OCP), polarization curves (PC) and electrochemical impedance spectroscopy (EIS). The results showed that the protective capacity of these polymeric systems on stainless steel, mainly with regard to pitting, depends on the nature of the anion dopant used during electro-synthesis of the PPy film. The best performance was seen with the dopants pTS and BS.     

Characterization of polypyrrole/piperazine-1,4-bis(2-ethane sulfonate) film and its application for the immobilization of vitamin B12

Vitamin B12 (B12) - possessing a redox active cobalt centre - is a candidate to be used as a mediator in bioelectrochemical processes. In order to exploit the possible redox activity of B12, Pt has been modified by a bio-conform conducting layer polypyrrole/piperazine-1,4-bis(2-ethane sulfonate) PPy/PIPES. The electrochemical and spectral behaviour of this film proved to be similar to PPy/dodecyl-sulfate (DS), widely considered and accepted as one of the best combinations of conducting polymer films. The capability of the PPy/PIPES film for acting as adsorbant in the accumulation of B12 has been evidenced by the electrochemical quartz crystal microbalance (EQCM) technique. B12 could also be incorporated into the polymer layer during its electrochemical deposition. The results proving the preserved redox activity of B12 within the film open new perspectives towards redox mediated bioelectrochemical applications based on the immobilization of this biomolecule.