Cyclic voltammetry polypyrrole

Table 3. Electrochemical data for AT-phenyl-substituted polypyrroles (all data from cyclic voltammetry using 0.1 M Et4NBF4 in acetonitrile exceptab).

Polythiophene films can be electrochemically cycled from the neutral to the conducting state with coulombic efficiencies in excess of 95% [443], with little evidence of decomposition of the material up to + 1.4 V vs. SCE in acetonitrile [37, 54, 56, 396,400] (the 3-methyl derivative being particularly stable [396]), but unlike polypyrrole, polythiophene can be both p- and n-doped, although the n-doped material has a lower maximum conductivity [444], Cyclic voltammetry shows two sets of peaks corresponding to the p- and n-doping reactions, with E° values at approximately + 1.1 V and — 1.4 V respectively (vs. an Ag+/Ag reference electrode)... 

Dynamic properties. On the basis of cyclic voltammetry, Diaz et al. (1981) showed that thin films of polypyrrole on an electrode immersed in acetonitrile could be repeatedly driven between the conducting and insulating states, as shown by the stability of the cyclic voltammograms of the films (see Figure 3.73). 

Electron transfer of the glucose oxidase/polypyrrole on the electrode surface was confirmed by differential pulse voltammetiy and cyclic voltammetry. The glucose oxidase clearly exhibited both reductive and oxidative current peaks in the absence of dissolved oxygen in these voltammograms. These results indicate that electron transfer takes place from the electrode to the oxidized form of glucose oxidase and the reduced form is oxidized by electron transfer to the electrode through polypyrrole. It may be concluded that polypyrrole works as a molecular wire between the adsorbed glucose oxidase and the platinum electrode. 

Cyclic voltammetry was performed with the ADH-NAD-MB/polypyrrole electrode in 0.1 M phosphate buffer (pH 8.5) at a scan rate of 5 mV s l. The corresponding substrate of ADH caused the anodic current at +0.35 V vs. Ag/AgCl to increase. These results suggest a possible electron transfer from membrane-bound ADH to the electrode through membrane-bound NAD and MB with the help of the conductive polymer of polypyrrole. 

These studies have been mainly carried out using cyclic voltammetry and frequency response analysis as experimental tools. As a typical example. Fig. 9.12 illustrates the voltammogram related to the p-doping process of a polypyrrole film electrode in the LiClQ -propylene carbonate electrolyte, i.e. the reaction already indicated by (9.16). 

Fig. 9.12 Cyclic voltammetry of the p-doping(anodic)-undoping(cathodic) process of a polypyrrole electrode in LiClO -PC solution. Pt substrate, Li reference electrode, scan rate 50 mV s .

Apart from the insulating polymeric matrices, conductive polymers such as polypyrrole and polyaniline have been used as nanocomposite electrodes by chemical or electrochemical polymerization [13, 17, 116, 117]. Such materials provide high conductivity and stability. However, the use of insulating polymers can be more advantageous than the conductive polymers when employed in cyclic voltammetry. 

Shinohara et al.52n suggested that the diffusion rate of dopant ions in polypyrrole films depends upon the size of the anion used as counter-ion in the electrochemical synthesis so that films prepared with CI counter-ions were impermeable to larger ions, at least in the time-scale of a cyclic voltammetry experiment. Tietje-Girault et al. 522) made two-layer polypyrrole films in which a layer was prepared with a large... 

Polypyrrole thin film doped with glucose oxidase (PPy-GOD) has been prepared on a glassy carbon electrode by the electrochemical polymerization of the pyrrole monomer in the solution of glucose oxidase enzyme in the absence of other supporting electrolytes. The cyclic voltammetry of the PPy-GOD film electrode shows electrochemical activity which is mainly due to the redox reaction of the PPy in the film. Both in situ Raman and in situ UV-visible spectroscopic results also show the formation of the PPy film, which can be oxidized and reduced by the application of the redox potential. A good catalytic response to the glucose and an electrochemical selectivity to some hydrophilic pharmaceutical drugs are seen at the PPy-GOD film electrode. 

Kapui et al. prepared a novel type of polypyrrole films [168]. The film was impregnated by spherical styrene-methacrylic acid block copolymer micelles with a hydrophobic core of 18 nm and a hydrophilic corona of 100 nm. The properties of the micelle-doped polypyrrole films were investigated by cyclic voltammetry and SECM. It was found that the self-assembled block copolymer micelles in polypyrrole behave as polyanions and the charge compensation by cations has been identified during electrochemical switching of the polymer films. 

Cyclic voltammetries (CVs) of CNTs A/CoSi700 modified by electrodepos-ited polypyrrole present the characteristic boxlike shape of an ideal capacitor even at moderate scan rates of 2 mV/sec, as shown in Figure 7.13 (Frackowiak and Beguin, 2002). Values of specific capacitance of nanotubes are significantly enhanced after modifications such as electrodeposition of a thin layer of conducting polymers, because of the contribution of pseudofaradaic properties of the polymer. 

Similar observations concerning the electro-oxidation of methanol were made by Ulmann et al, using platinum micro-particles dispersed into polypyrrole films (from 100 to 700 nm thickness) deposited by cyclic voltammetry on a gold electrode [152]. The platinum loading was varied from 10 pg/cm to 300 pg/cm, leading to an increase in the current density (recorded after 12 hours of methanol oxidation at a constant potential) for platinum loadings up to 150 pg cm after which the current density reaches a plateau. 

Figure 13 shows the steady-state A-E curves for the redox reaction of Cyt c at a polypyrrole-methylene blue CME." From Fig. 13, the redox processes of Cyt c, which cannot be detected by cyclic voltammetry owing to the large background current, can be directly monitored. The values of A p obtained from the inflection points is about 60 mV. Because A p < 200 mV, Eq. (25) is used to determine itjj, which gives a value of 5.4 X 10 cm sec . " The determination of kinetic parameters for other redox proteins by CPS/SSCA at various types of CMEs is discussed in the following section. 

Y.C. Liu, BJ. Hwang, W.J. Jian, and R. Santhanan, In situ cyclic voltammetry-surface-enhanced Raman spectroscopy studies on the doping-undoping of polypyrrole film. Thin Solid Films, 374, 85-91 (2000). 

M.D Levi, C. Lopez, E. Vieil, and M.A. Vorotyntsev, Influence of ionic size on the mechanism of electrochemical doping of polypyrrole films studied hy cyclic voltammetry, Electrochim. 

In order to immobilize enzymes in conducting polymers to fabricate biosensors, the electrochemical synthesis of polypyrrole films was studied under different conditions. It was found that the size and morphology of polypyrrole films synthesized using cyclic voltammetry were affected by the concentration of the supporting electrolyte at a scan potential range between 0.0 and 1.0 V (vs. SCE), and at a scan rate of 48 mV s [47]. The diameters of particles prepared in a solution containing 0.10 M pyrrole and 0.10 M NaCl... 

The fabrication of polypyrrole wires via electropolymerization within poly(methyl methacrylate) nanochannels on an indium tin oxide (ITO) substrate was reported by Chen et al. [53]. The electrochemical synthesis of polypyrrole was performed by a cyclic voltammetry method in aqueous 0.1 M NaC104 containing 0.1 M pyrrole monomer. The potential was scanned 10 times between -0.7 and +0.6 V vs. Pt at a scan rate of 100 mV s . The nanochannels act as templates for electropolymerization of polypyrrole nanowires. 

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