Polypyrrole Film Electrodes Research Articles

Platinum–palladium loaded polypyrrole film electrodes for the electrooxidation of d-glucose in neutral media

Abstract Modified polymer films with metal particles incorporated into the films by electrodeposition are known as possible electrocatalysts for various electrode reactions such as fuel cell applications. This work presents some results concerning the electrooxidation of d -glucose at modified polymer film electrodes prepared on a platinum substrate. This reaction has a great deal of interest in view of its applications to detection systems (glucose sensor), fuel cells (pacemakers) and electroorganic systhesis. The modified polymer film electrodes contain platinum and/or palladium particles dispersed in the polypyrrole film by electrodeposition in neutral media. Addition of palladium to platinum modifies the electrocatalytic behaviour of the electrode drastically. The modification is thought to involve minimisation of the poisoning of the catalyst, hence increasing its electrode activity.

Electrochemical preparation and characterization of polypyrrole doped with bis(trifluoromethanesulfone) imide anions

Polypyrrole-bis(trifluoromethanesulfone)imide, PPy-TFSI, thin film electrode was prepared electrochemically by potential cycling or galvanostatically at a platinum electrode from a 0.5 M pyrrole/ 0.1 M lithium bis(trifluoromethanesulfone)imide, LiTFSI, /acetonitrile solution. The TFSI anion was selected as a dopant for polypyrrole because previous studies have shown that such polymer has a high electrical conductivity. The resulting PPy-TFSI film electrodes were characterized by scanning electron microscopy, cyclic voltammetry and electrochemical impedance spectroscopy. The apparent redox potential for a TFSI-doped polypyrrole film is slightly shifted to more positive potential in comparison to a perchlorate-doped film. This is related to the high delocalization of the charge of the TFSI anion which results in weaker anion–cationic polymer coulombic interactions. The low frequency capacitance and ionic resistance of the TFSI-doped polypyrrole are comparable to those reported for other polypyrrole film electrode.

Polymers of Platinum Metals Complexes Immobilised on Electrodes

Interest is growing in using polymeric electrode materials containing platinum group metals complexes in molecular electrochemistry. Here, the synthesis of functionalised polypyrrole film electrodes, formed by the oxidative electropolymerisation of pyrrole-substituted rhodium, iridium and palladium complexes is reviewed, and recent results are presented concerning the electrocatalytic reduction of protons and the hydrogenation of unsaturated organic substrates in aqueous electrolyte. Metal hydride intermediates and their involvement in reactions at the electrodes are considered, as are preliminary results of asymmetric electrosynthesis on a molecular electrode material.

Electrochemical studies of a lanthanide heteropoly tungstate/molybdate complex in polypyrrole film electrode and its electrocatalytic reduction of bromate

An electrode modified with a polybasic lanthanide heteropoly tungstate/molybdate complex K10H3[Nd(SiMo7W4O39)2] entrapped into polypyrrole (PPy) film, denoted as Nd(SiMo7W4)2-PPy, exhibits three couples of two-electron redox waves in pH 1–5 buffer solutions. The redox waves are surface-controlled at lower scan rates and diffusion-controlled at higher scan rates. The effects of pH on the electrochemical behavior of Nd(SiMo7W4)2 in PPy film were investigated in detail and compared with that of Nd(SiMo7W4)2 in aqueous solution. The various charge states of PPy during its redox process have peculiar effects on the relationship between pH and formal potentials of Nd(SiMo7W4)2-PPy at different acidities. The Nd(SiMo7W4)2-PPy cme can remarkably catalyze the electrochemical reduction of bromate with good stability.

Increased Redox-Reaction Rate of Quinhydrone at N-Substituted Polypyrrole Film Electrodes

Abstract A poly[1-methyl-3-(pyrrol-1-ylmethyl)pyridinium] perchlorate-coated glassy carbon electrode noticeably decreased the charge-transfer resistance (Rt) of quinhydrone relative to a naked glassy carbon electrode. The redox species was not concentrated into a polymer film; this result differs markedly from the very good absorption of anthraquinonesulfonates and indigosulfonates by a polymer film. The dependence of Rt and the interfacial capacitance on the film thickness implies that the charge-transfer process occurs at the film-solution interface, because the polymer film is appreciably electronically conductive at positive potentials. Because of a change in the film conductivities with the potential, the polymer-coated electrode increased the anodic peak current of quinhydrone by three times, but decreased its cathodic peak current by two fifths, relative to that of a naked electrode. Although the decrease in Rt at a polymer-film electrode is somewhat ascribed to an increasing area, which is due to a porous film surface, the electrocatalytic effect of the polymer film can be attributed to an increasing standard rate constant of the charge-transfer process; this increase may be due to the adsorption of quinhydrone on the polymer surface.

A ferrocene crown ether–functionalized polypyrrole film electrode for the electrochemical recognition of barium and calcium cations

Transfer of the recognition activity of a ferrocene ionophore to an electrode surface from the homogeneous phase has been successfully accomplished for the first time. The synthesis and electrochemical characterization of a new pyrrole‐substituted ferrocene crown ether are described, followed by the formation of the corresponding polymer film modified electrode. It is shown that the electrode exhibits amperometric recognition in an organic solvent of Ca2⊕ and Ba2⊕ among the alkaline and alkaline earth metal cations.

Electrocatalytic reduction of nitrite using Dawson-type tungstodiphosphate anions in aqueous solutions, adsorbed on a glassy carbon electrode and doped in polypyrrole film

The electrochemical behavior of Dawson-type P 2W 18O 6− 62 adsorbed on a glassy carbon electrode and doped in a polypyrrole film electrode was described. These modified electrodes all display catalytic activity for nitrite reduction, either in acid solutions or in pH > 4.0 solutions.

Selectivity and sensitivity of ultrathin purine-templated overoxidized polypyrrole film electrodes

Ultrathin overoxidized polypyrrole (OPPy) films templated with adenosine, inosine and adenosine 5′-triphosphate (ATP), grown on glassy carbon (GC), have been characterized. High sensitivity for ruthenium hexaamine, uric acid and adenine at the ultrathin film electrodes indicates that the interactions with the film rather than in-film transport controlled the response of the film electrodes in slow scan voltammetry. The high sensitivity at the film electrodes allowed the analysis of the effect of templating on the probe-film interactions. The results show that templating with purines changes the selectivity and sensitivity of OPPy films. It is demonstrated that templating with ATP, via electrostatic interactions of ATP with the positively charged PPy, has a most significant effect on the response of the OPPy films, and the ATP-templated films show high selectivity to adenine. The sensitivity for adenosine is significantly enhanced at OPPy films considering that the response is not apparent at the bare glassy carbon.

Analysis of the long-term potential stability of an all-solid-state potassium-selective electrode with electroactive polypyrrole film

By coating an electroactive polypyrrole (PPy) film electrode with a plasticized poly(vinyl chloride) (PVC) membrane containing valinomycin, an all-solid-state potassium-selective electrode was fabricated. The polymerizing conditions of the PPy film were optimized for stable ionic responses. The electrochemical characteristics of these electrode systems were evaluated by an a.c. impedance method with respect to the mechanism of potential drift. The steady-state response over several days, which depended on the electrode configuration, was related to the impedance behavior of the electrode systems.

Charge Transport at Polypyrrole Film Electrodes: Effect of the Electrolyte Concentration

Abstract From measurements of the a.c. response of polypyrrole film electrodes in KNO3 solution, we found that solvent swelling of the polymer greatly influences the kinetic behaviors of the polymer film electrodes. Electric migration in bulk film was due to background electrolyte ions which permeated through the film. Inside the film in contact with a supporting electrolyte solution, the mobility of the electrons may be much smaller than that of ions. The charge-transfer resistance of a partially oxidized film decreases along with increasing concentration of the electrolyte solution, because of a resultant increase in the activity of polarons. Such an increased activity of polarons also brings about a smaller Warburg coefficient, and thus a smaller limiting diffusion resistance (RL). The pseudocapacitance appearing at low frequencies increases along with an increase in the concentration of the electrolyte solution, which is opposed to the change in RL. These results corroborate that variations in the charge-transport parameters with the electrolyte concentration can be ascribed to an increase in the polaron activity with increasing ion concentration inside the polymer film.

Control of selectivity and electroactivity on underoxidized polypyrrole film electrodes

AbstractNeutral (or under‐oxidized) PPY film electrodes were directly prepared by electropolymerization and elimination of the subsequent oxidation of the deposited PPY layers during the polymerization process. Electroactivity and selectivity could be established on these nonconducting, densely packed neutral PPY film electrodes through controlled oxidation. Development of electroactivity for different redox solutes was concluded to be a combination of the creation of conducting areas and the opening of transport channels in the neutral PPY network by the oxidation. Selectivity of the PPY film electrode was controlled by selection of electrolyte counter‐anion, management of molecular size, and change of pH.

Electrical conductivity of poly(vinyl chloride) obtained by photodehydrochlorination from laminated poly(vinyl chloride)/polypyrrole films

AbstractPoly(vinyl chloride) (PVC) has been converted to an electrically conductive structure by combined electrochemical and photochemical methods. PVC was cast on a polypyrrole (PPy) film electrode which had been electrochemically prepared. The PVC layer in the laminated PVC/PPy films was first dehydrochlorinated under the illumination of UV light, and the generated polyenes were subsequently doped with I2 and FeCl3. The maximum electrical conductivity achieved for such PVC film was 2.51 X 10−2 and 8.63 10−2 S cm−1 after I2 and FeCl3 doping, respectively. The temperature dependence of the electrical conductivity showed different behavior in higher and lower temperature ranges. In the former (T > 243 K), the T−1 law held, and the activation energy and bandgap were estimated as 0.25 and 0.49 eV, respectively. In the latter (T < 243 K), the conductivity mechanism followed the variable range hopping model (T−1/4 law) in which the radius of the localized state wave function and the density of the localized states at the Fermi level were 1.25 × 103 Å and 1.03 X 1015 eV−1 cm−3, respectively. © 1995 John Wiley & Sons, Inc.

Characterization of Charge Transfer and Charge Transport in Polypyrrole Film Electrodes

Abstract The a.c. response of polypyrrole film electrodes in 0.2 M KNO3 was investigated at different applied potentials and film thicknesses. The results of impedance analysis on the basis of the Randles equivalent circuit indicated that the electron exchange between a metal and the polymer controlled the rate of charge-transfer process at the film electrode. Accordingly, the oxidation of the polymer proceeds from the back of the film to its surface. The resistance due to electric migration in the film strongly depended on the concentration of the supporting electrolyte; this dependence suggests that the migration is ionic. This effect may be due to a change in the solvent swelling of the polymer. The oxidation of the polymer brought about each decrease in the charge-transfer resistance at a metal–polymer interface and the limiting resistance associated with the diffusion of charge carriers. The low-frequency pseudocapacitance of the polymer increased with increasing oxidation level and film thickness, which was expected from a finite diffusion model.

Amperometric detection of catecholamines with liquid chromatography at a polypyrrole-phosphomolybdic anion-modified electrode

A conducting polypyrrole film immobilized with PMo 12O 40 3− anion on a glassy carbon electrode was prepared by an electrochemical method. This kind of chemically modified electrode (CME) was prepared successfully by doping the polypyrrole film electrode with heteropolyacid under a cycling potential between −0.2 and +0.6 V in 0.5 mol l −1 H 2SO 4 containing Na 3PMO 12O 40 dopant. The experimental results show that an electrode modified with a heterophosphomolybdic acid-polypyrrole film has a catalytic effect on the oxidation-reduction of catecholamines. When employed with a dual-electrode arrangement in liquid chromatography with electrochemical detection using the PPy-PMo 12O 40 3− electrodes as generating and collecting detectors, high effective collection efficiencies for catecholamines were achieved with a linear response range over three orders of magnitude and a detection limit of 5.0 X 10 −9 mol l −1 for norepinephrine. The amperometric response showed very good sensitivity and stability for catecholamine detection.

Electroanalysis of metal species at polypyrrole-modified electrodes

Conducting-polymer-modified electrodes based on the incorporation of two anionic ligands, namely bathophenanthroline disulfonate and bathocuproine disulfonate, into polypyrrole film during electropolymerization were found to show sensitivity to copper species (both Cu + and Cu 2+ ions). The copper species were readily extracted into the polypyrrole film electrode containing the complexing ligands. The electrochemical reaction of the incorporated copper complex resulted in a measurable square-wave voltammetric peak current, which was found to be related to the logarithm of copper concentrations. Reproducibility of the determination of copper species by the ligand-incorporated polypyrrole-modified electrodes was around ± 11% RSD and the detection limit was estimated to be about 2 μM.

Characterization of 1:12 Phosphomolybdic Anions Doped Polypyrrole (PMo<sub>12</sub>/PPy) Film Electrode

1:12 phosphomolybdic anion doped polypyrrole film electrode was characterized by in-situ UV-vis spectroelectrochemistry, X-ray photoelectron spectroscopy(XPS), scan electronic microscopy(SEM) and electron spin resonance(ESR) spectroscopy.

Study of a 1 : 12 phosphomolybdic anion doped polypyrrole film electrode and its catalysis

A phosphomolybdic anion doped polypyrrole (PMo 12O 40 3− + PPy) film electrode has been prepared by electrochemical polymerization of pyrrole in an aqueous solution of 0.5 mol l −1 H 2SO 4 or 0.5 mol l −1 KNO 3 containing PMo 12O 40 3− anions, and characterized by scanning electron microscopy and in-situ UV-visible spectroelectrochemical methods. The film electrode obtained is very stable upon potential cycling in acidic solution, but not in neutral solution. The catalytic effect of the film electrode on the reduction of ClO 3 − and BrO 3 − was studied.

The reduction of dioxygen and the oxidation of hydrogen at polypyrrole film electrodes containing nanodispersed platinum particles

Polypyrrole (ppy) films containing a three-dimensional array of nanometer-sized platinum catalyst particles have recently been developed in this laboratory. The catalytic activity of these “nanocomposite” (ppy+Pt) films towards the dioxygen reduction reaction (ORR) and the hydrogen oxidation reaction (HOR) was tested in 0.05 M H 3PO 4 and 0.5 M H 2SO 4 respectively, with the polymer film thickness and platinum catalyst loading as variables. In both cases an increase in the reaction cross-section with the polymer film thickness was noted, consistent with the facile permeation of the substrates into the polymer+catalyst framework. The hydrodynamic voltammetry data were analyzed and found to be diagnostic of rate control being exercised by the bimolecular catalyst-substrate charge-transfer reaction for both the ORR and HOR. For the HOR, the ppy + Pt. films exhibited a remarkable enhancement (five times) in the reaction rate relative to a massive platinum comparison standard. While polypyrrole itself showed negligible catalytic activity towards the HOR, the ORR proceeded at a fast rate at the polymer matrix even in the absence of the platinum catalyst. Comparisons with available data on the ORR and HOR at other types of platinum modified polypyrrole samples are presented.

Polypyrrole film electrodes electrochemically doped with tetrathiomolybdate anions: preparation and characterization

Polypyrrole films containing tetrathiomolybdate anions and molybdenum trisulfide have been prepared on platinum and tin oxide coated glass electrodes by anodic electrochemical deposition from an aqueous solution containing pyrrole and ammonium tetrathiomolybdate. The scanning electron micrographs of these films show a porous structure. Cyclic voltammetry at a tin oxide electrode in a solution containing pyrrole and tetrathiomolybdate suggests that the formation of the polymer proceeds initially by a nucleation process. The current-time transient for film deposition remains fairly constant for long elapsed times, after the initial decrease and rise, indicating the formation of a fairly conducting layer. A linear relationship is observed between both film thickness, the weight of molybdenum in the polypyrrole-tetrathiomolybdate film and the charge passed during film formation. The cyclic voltammogram of the polypyrrole-tetrathiomolybdate film is characterized by an apparent redox potential, taken as the average between the anodic and cathodic peaks, of approx. −0.3 V vs. SCE. The latter is shifted to a more negative potential in comparison with that of a polypyrrole-chloride film electrode. This negative shift is characteristic of polypyrrole film doped with some “immobile” dopant. In this case the redox processes involve insertion of cations from the supporting electrolyte during film reduction and expulsion during oxidation. This was confirmed by cyclic voltammetry which is strongly dependent on the size of the electrolyte cation and independent of the electrolyte anion. Elemental analysis shows that the polypyrrole-tetrathiomolybdate film contains 70% MoS 3 and 30% MoS 4 2− relative to the molybdenum content. The conductivity of a polypyrrole-tetrathiomolybdate film is at least two orders of magnitude larger than that of a molybdenum trisulfide film.

Modification des polymères conducteurs avec de petites particules métalliques; propriétés des films de polypyrrole et de polyaniline platines

The properties of two π-conjugated conducting polymers, polypyrrole, and polyaniline, modified with small amounts of Pt, have been investigated. Both polymers were prepared by electrochemical (cyclic voltammetric) polymerization in the form of thin films (less than 1 μm for polypyrrole, ca. 50-μm thick for polyaniline). It is shown that incorporation, via electrodeposition, of small amount of dispersed Pt particles, inside the polymer film, leads to radical change of its properties. Thus, the polypyrrole film electrode containing ca. 200 μg · cm-2 of Pt exhibits remarkably stable electrocatalytic activity towards anodic oxidation of an important fuel cell reactant – CH3OH. In contrast with the bulk Pt metal or the Pt dispersed on other supports, a polypyrrole/Pt composite does apparently not undergo poisoning, even in the course of prolonged oxidation runs. We show also that the incorporation of Pt microparticles, into several tens of μm thick polyniline films, results in a large enhancement of their redox switching rate between isolating and conducting states and vice versa.