Polypyrrole In Aqueous Solution Research Articles

Electrochemical preparation and redox/ion exchange properties of polypyrrole in aqueous sodium hexafluoroaluminate

Electrodeposition and redox switching performance of polypyrrole in aqueous solution of sodium hexafluoroaluminate are described. An incorporation of NaAlF62− into the polymer phase is indicated by the EQCM analysis of electrodeposition. A SEM micrograph shows a characteristic morphology of the polymer layer. A mechanism of the redox process of polypyrrole is discussed based on CV and EQCM results involving the measurements performed as a function of a time scale of the redox cycle and a life time of the electrode. Structure determining interactions between polymer sites and counterions are indicated. Participations of ion-pair counterion, co-ion, salt, water, oxygen in the redox process of polypyrrole are discussed. A slow irreversible rearrangement in the structure/composition, inducing a change in the mechanism of the reversible redox process, is postulated to occur during the reduction process of the virgin anion-exchanging polypyrrole. Long time scale processes were observed to result in cation exchange properties accompanied by a substantial decrease in redox activity and/or CV currents of the polypyrrole electrode. The performance of the primary hexafluoroaluminate counterion electrode, prepared in aqueous solution of sodium hexafluoroaluminate, is compared to the secondary hexafluoroaluminate counterion electrode, prepared in a presence of the sodium chloride solution. In general, the CV and EQCM characteristics of the two system are similar due to pronounced contribution of the bathing electrolyte to the performance of the polymer electrode.

Surface Electric Properties of Polypyrrole in Aqueous Solutions

The electric properties, for example, ζ potential and surface charge, of a solid in contact with an aqueous solution play an important role in various interfacial and colloidal phenomena, as well a...

Enhanced electrical conductivity of polypyrrole prepared by chemical oxidative polymerization: effect of the preparation technique and polymer additive

The electrical conductivity of chemically prepared polypyrrole in aqueous solution was found to be strongly dependent on the preparation technique and polymer additive. Owing to the hygroscopic nature of polypyrrole, it is essential to remove residual water. Accordingly, the conductivity can be enhanced by about two orders of magnitude when using a preparation technique that includes a washing treatment with organic solvents and drying under vacuum at elevated temperatures to attain maximum removal of water. Thus, the electrical conductivity of polypyrrole is affected not only by reported factors such as the ratio of oxidant to pyrrole, reaction temperature, and reaction time, but also by the preparation technique. Additionally, a significant enhancement of the conductivity up to 90 S cm −1 by using of poly(ethylene glycol) as an additive during the polymerization could be achieved.

In-situ electrochemical studies on the redox properties of polypyrrole in aqueous solutions

Two electropolymerization techniques have been used in preliminary research on polypyrrole, such as potential cycling and galvanostatic modes. The cyclic voltammograms and chronopotentiograms can describe the proceeding of the growth of polypyrrole from various aqueous solutions. The cyclic voltammetry of a polypyrrole film in an electrolyte solution can further characterize the polypyrrole films electrochemically. Some evidence has been shown of doping with cations. Polypyrrole differs with respect to the extent of oxidation, doping anions, and also reduction, doping cations. Such properties can be switched dynamically between anion and cation coupling or hopping through electrochemical oxidation and reduction of the polypyrrole backbone.

The role of a silane coupling agent in the synthesis of hybrid polypyrrole–silica gel conducting particles

The preparation of new hybrid conducting polymer–silica gel particles is described. The silica gel acts as a high surface area substrate (431 m2 g–1) for the in situchemical synthesis of conducting polypyrrole in aqueous solution in order to obtain hybrid polypyrrole–silica particles. The role of a common silane coupling agent (i.e. aminopropyltriethoxysilane, APS) in the pretreatment of silica gel prior to polymerization and preparation of polypyrrole–APS–silica particles is also investigated. It was found by TGA that the polypyrrole mass loading is higher in polypyrrole–APS–silica than in polypyrrole–silica particles. XPS results indicated that APS-treated silica leads to polypyrrole-rich surface particles not found with the untreated silica. Consequently, the polypyrrole–APS–silica pellets were three orders of magnitude more conductive than those of polypyrrole–silica.The surface area of the polypyrrole–silica (422 m2 g–1), as measured by BET, matched that of the untreated silica whilst that of the polypyrrole–APS–silica (162–184 m2 g–1) is significantly lower. The combination of XPS, TGA, BET and conductivity measurements suggest that pyrrole is predominantly polymerized in the pores of the untreated silica gel whilst the APS pretreatment of silica leads to the formation of a thin overlayer of polypyrrole at the surface of the silica gel in addition to a higher conducting polymer loading in the gel pores.

EQCM studies on polypyrrole in aqueous solutions

Electrochemical quartz crystal microbalance (EQCM) studies revealed that the electrochemical properties of polypyrrole (PPY) in aqueous solutions are greatly dependent on the solution pH. A PPY film immersed in an aqueous KCl solution shows redox processes which involve not only anion transport but also cation transport if the solution pH is greater than 3–4, whereas at lower pH values only anion transport prevails as has been widely recognized. It has been found from comparative studies using poly( N-methylpyrrole) that protonation and deprotonation at nitrogen atoms of PPY play a key role in the observed pH-dependent electrochemical behavior. Deprotonated PPY allows transient incorporation of hydrated cations upon reduction in weak alkaline aqueous solutions, followed by slow ejection of the incorporated cations when conventional electrolytes such as KCl and NaClO 4 are used, but not in NH 4Cl solution. Discussion on the cation transport in PPY is made in terms of deprotonation and protonation of nitrogen atoms of pyrrole subunits in PPY.

Studies on the electrode kinetics of polypyrrole in aqueous solution by a.c. impedance measurement

Electrode kinetics of PPy(Cl −) film in acidic and neutral solutions has been studied by the a.c. impedance method. The values of the charge transfer resistance and diffusion coefficient of counter-ions in the PPy film depend on the pH value of the solution in contact and on the potential applied. The exchange current density i o of the PPy film electrode is 1.15 mA cm −2 and the apparent diffusion coefficient D app of the counter-anion is 1.8 × 10 −9 cm 2s −1, in a pH 3, 0.5 M KCl solution at 0.1 V(SCE). Both i o and DP app decrease with decrease of applied potential. In a neutral solution, two redox processes can be distinguished in the a.c. impedance plots.

In situ spectroscopic investigations of the growth, electrochemical cycling and overoxidation of polypyrrole in aqueous solution

In this paper, we present results from in situ ellipsometry and Fourier Transform Infra Red spectroscopy on the growth, electrochemical cycling and overoxidation of polypyrrole in 1M NaClO 4. The data show that the initial charge-carrying species are polarons. At higher potentials, bipolarons are also formed, and co-exist with the polarons; strongly suggesting that there is no appreciable energy gain in forming a bipolaron (with respect to two polarons). Both species have narrow, well-defined conjugation lengths, with bipolarons being ca 9 monomer units smaller than polarons. The oxidation of the polypyrrole results in the expulsion of solvated protons from the film, via the deprotonation of water; in addition, oxidation of the film is accompanied by a reversible 30% reduction in its thickness, a quite unexpected result in a view of the necessity for charge compensation through ingress of solvated anions. Ellipsometry shows that the major changes in L occur between −0.2 V and +0.2 V, ie at potentials associated with strong growth in bipolaron rather than polaron concentration. A model is postulated in which the major cause of the contraction is electrostriction, associated with the formation of bipolarons. That is, in turn, initiated by the generation of a critical concentration of polarons. The kinetically fast proton expulsion that takes place in the early part of the oxidation process is superseded at higher potentials by the thermodynamically-favoured influx of anions. Overoxidation of polypyrrole in aqueous solution results in the formation of pyrrolinones, with a range of short conjugation lengths, and CO 2 (from the complete oxidation of end-groups); as well as an influx of solvent into the film, which expands. Eventually, the pyrrolinone segments are also oxidized to CO 2, but the mechanical integrity of the polymer is maintained.

Complexation of electroconducting polypyrrole with copper

A copper complex of polypyrrole is obtained when the polymer perchlorate is treated with a Cu(II)-containing alkaline solution. The X-ray photoelectron spectrum of the resulting polymer material shows that the copper atoms are coordinated to pyrrole nitrogen. The ESR signal of copper ions and that of the pyrrole rings are observed independently of each other; there is no appreciable magnetic interaction between the two paramagnetic species. The room-temperature conductivity is 4 × 10 −4 S cm − and the temperature dependence shows semiconductive behavior with an activation energy of 0.11 eV. The degradation of conducting polypyrrole in aqueous solution is suppressed by the presence of copper: the stabilization is attributed to CuN bond formation.

Effect of anion and solution pH on the electrochemical behavior of polypyrrole in aqueous solution

The electrochemical behavior of polypyrrole (PPy) in aqueous solution has been found to be remarkably affected by the type of intercalating anion and pH of the solution by in-situ VIS-NIR absorption spectroscopy and cyclic voltammetry. In an acidic solution reversible electrochemical deintercalation and reintercalation of anions out of and into PPy were observed for the anions of Cl −, NO 3 −, ClO 4 − etc. in the potential range of −0.9 to +0.3 V vs. SCE. However, re-intercalation of TsO − was found to be difficult. In a basic solution the counter anions in PPy as prepared were exchanged by OH − from solution and subsequent electrochemical redox cycling involved the de-intercalation and re-intercalation of OH −. In neutral solution, two pairs of redox peaks existed in the cyclic voltammogram, perhaps the electrochemical processes of both original anion and OH − were involved.

Electrochemically behaviour of oxidized polypyrrole in aqueous solutions

Electrochemical generation of oxidized polypyrrole (PPy) on a Pt electrode from aqueous solutions has been studied by cyclic voltammetry with 0.1 M HClO 4, TsOH, 1 2 H 2SO 4, TsONa and 1 2 Na 2SO 4 as supporting electrolytes. It is found that when the working electrode potential was scanned to higher than +1 V versus SCE, the oxidized PPy film underwent an irreversible oxidation leading to chemical structure change and possibly some degradation of the film. The oxidative stability of the oxidized PPy film varied with the supporting electrolyte used in the generation and decreased in the following order: HClO 4, TsOH, H 2SO 4, TsONa and Na 2SO 4. More or less reversible de-intercalation and re-intercalation of the counter ion of the oxidized PPy film electrochemically generated from TsOH have been observed during repeated cyclic voltammetric scans from +0.2 to −0.7 V versus SCE of the PPy film electrode in 0.1 M TsOH and in pH 12.0 NaOH solution.