Polypyrrole film cyclic voltammogram

Figure 18. Cyclic voltammograms of a polypyrrole film in propylene carbonate containing 0.5 M UCIO4.97...

If the film is nonconductive, the ion must diffuse to the electrode surface before it can be oxidized or reduced, or electrons must diffuse (hop) through the film by self-exchange, as in regular ionomer-modified electrodes.9 Cyclic voltammograms have the characteristic shape for diffusion control, and peak currents are proportional to the square root of the scan speed, as seen for species in solution. This is illustrated in Fig. 21 (A) for [Fe(CN)6]3 /4 in polypyrrole with a pyridinium substituent at the 1-position.243 This N-substituted polypyrrole does not become conductive until potentials significantly above the formal potential of the [Fe(CN)6]3"/4 couple. In contrast, a similar polymer with a pyridinium substituent at the 3-position is conductive at this potential. The polymer can therefore mediate electron transport to and from the immobilized ions, and their voltammetry becomes characteristic of thin-layer electrochemistry [Fig. 21(B)], with sharp symmetrical peaks that increase linearly with increasing scan speed. 

Figure 21. Cyclic voltammograms (at 20to lOOmVs-1)of [FefCNJd3"74-electrostatically trapped in polypyrrole films with an alkyl pyridinium substituent at the (A) 1 - or (B) 3-position.243 (Reprinted with permission from J. Phys. Chem. 96, 5604-5610, 1992 Copyright 1992, American Chemical Society.)...

Cyclic voltammetric studies involving polymers, 558 and the nature of charge carriers, 561 and the nucleation loop, 557 of poly (3-methylthiophene), 564 and parallel-band electrodes, 570 Cyclic voltammograms as a function of scan rate, 559 involving polymerization, 559 with polyanaline, 566 of polypyrrole film, 581... 

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). 

Figure 3.74 Cyclic voltammograms of a 20nm-thick polypyrrole film on Pt in CHjCN containing different electrolytes. Two sweep rates are shown, the voltammograms showing the tower currents were taken at 50mVs , and the larger currents were obtained at lOOmVs"...

Typical voltammograms of a polypyrrole him obtained by the authors are shown in Figure 3.81. If the film was held at —0.6 V vs. SCE prior to cycling, the cyclic voltammogram showed a definite peak, near c. - 0.15 V, as was observed by other workers and is discussed above. The potential at which this peak occurs was found to mark a definite transition point in the behaviour... 

Figure 3.81 Typical cyclic voltammograms of a poly pyrrole film on Pt in Nrsatu rated 1 M NaClOj. The voltammograms were collected immediately after holding the film at -0.6 V vs, SCE for 5 min and after cycling for 5 min. The scan rate was 100 mV s "1 and the film thickness 84 nm. Reprinted from Electrochimica Acta, 36, P.A, Christensen and A. Hamnett, In situ Spectroscopic Investigations of the Growth, Electrochemical Cycling and Overoxidation of Polypyrrole in Aqueous Solution , pp. 1263-1286(1991), with kind permission from Pergamon Press Ltd., Headington Hill Hall, Oxford OX3 0BW, UK.

Thus, it appears that the transition represented by the anodic peak in the cyclic voltammogram of polypyrrole is due to a changeover in the dominant carrier type and is accompanied by a dramatic contraction of the film. The authors strongly suspected that this contraction was due to electro-striction associated with bipolaron formation. As a further test they also carried out experiments intended to test if proton expulsion from the film occurred on oxidation. They found that it did indeed occur but monotonically at alt potentials > -0.6 F, in agreement with the extremely elegant work of Tsai et at. (1987), and so could not be responsible for the relatively sudden contraction at potentials > —0.2 V. 

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). 

Polypyrrole Film Formation in Glucose Oxidase Enzyme Solution. Cyclic voltammograms recorded in the GOD and pyrrole solution showed an anodic peak current (E = 1.08 V), which suggested the polymerization of pyrrole in the above solution. However, the polymerization potential moved toward the more positive direction compared to the polymerization potential of PPy doped with Cl ( pa < 1.0 V). This is due to the fact that the polymerization is more difficult to take place in enzyme solution than in Cl solution because the enzyme solution is a much weaker electrolyte than NaCl it may also be due to the less conductive nature of the PPy-GOD film as compared to that of the PPy-Cl film. The polymerization current level was much lower in the enzyme solution than in the Cl solution because of the poor charge-transport property of the enzyme protein molecules. It was found that the constant current method was more suitable than the controlled potential method for making the PPy-GOD film on the GC electrode. 

Figure 11.19 High frequency part of capacitance and resistance of a polypyrrole film as function of the potential. The film was prepared by anodic oxidation in a perchlorate electrolyte. Additionally, the cyclic voltammogram is shown. The film has metal-like properties at positive potentials (E> OV) and neutral state properties at negative potentials (E < -0.5 V).

FIGURE 6.14. Experimental cyclic voltammograms for a 1 -//m-thick polypyrrole film in 1 mol.dm ... 

FIGURE 7.6. Typical cyclic voltammograms of a polypyrrole film on a platinum foil electrode in N2-saturated IM NaC104. Voltammograms were collected immediately after holding the film at-0.6 V for 5 minutes and cycling for 5 minutes scan rate 100 mV/s, film thickness 84nm. (From Ref 20)... 

FIGURE 18.3 Comparison of cyclic voltammograms of polypyrrole (PPy) films in classical electrolyte and ionic liquids. Scan rate 100 mVs . (Reprinted from Pringle, J.M., J. Efthimiadis, PC. Howlett, D.R. MacFarlane, A.B. Chaplin, S.B. Hall, D.L. Officer, G.G. Wallace, and M. Forsyth. Polymer, 45,1447-1453, 2004. With permission.)... 

The electrochemical characterization of the polypyrrole films doped by anionic complexes was generally achieved by cyclic voltammetry. Unfortunately, no well-defined waves for the porphyrin or phthalocyanine redox couples were observed which may be because they are superimposed on the large polypyrrole background. Therefore, the reported voltammograms could either be those for the redox process of the incorporated complexes or those of the... 

Cyclic voltammetry can be used to estimate the charge transfer rate and also evaluate how this rate depends on parameters such as morphology and the chemical structure. The cyclic voltammetric examination of electroactive polymers is usually done in monomer-free solutions containing only the solvent and supporting electrolyte. In order to avoid the complication of mixed electrolytic equilibria, the supporting electrolyte and the solvent are usually the same as employed for the polymerization. Figure 3 shows the cyclic voltammogram (CV) of a polypyrrole film prepared in acetonitrile/tetra-w-butyl ammonium fluoborate medium. The anodic peak corresponds to polypyrrole oxidation, while the cathodic one corresponds to the reduction of this species. 

FIGURE 3 Cyclic voltammogram of a polypyrrole film with fluoborate counterion. Medium tetra- -butyl ammonium tetrafluoborate (0.1 M) in ACN. Scan rate 100 mV/s. Potential referred to Ag/Ag" electrode. (Data from Ref. 38.)... 

The redox behavior of polythiophene and substituted polythiophenes (mainly 3-alkyl substituted) is closely related to that of polypyrrole, as might be expected. The cyclic voltammogram of polythiophene [42] shows that oxidation of the polymer occurs at 1.0 V versus SCE whereas reduction occurs at 0.9 V. Past 1.71 V, another peak appears, and if the potential of the film is taken beyond this value, deactivation of the film occurs. But in another aspect polythiophene differs from polypyrrole. It shows better redox activity when there is a substituent in the ring. In fact, the processibility (ability to spin cast films etc.) also improves, especially if there are hexyl or octyl groups substituted at the 3-position. 

FIGURE 7 (a) Cyclic voltammogram of a polypyrrole film doped with ferricyanide ion. Medium 0.1 M KCl (aq). (b) Cyclic voltammogram of the same film in KCl solution after reduction at -1 V for 5 h. Potentials are referred to Ag/AgCl. Scan rate 50 mV/s. Film thickness 30 /txm. Area (geometric) of electrode I cm. (With permission from VCH Publishers, Weinheim, Germany, Ref. 29.)... 

A typical cyclic voltammogram is shown in Fig. 2 for a polypyrrole film. The polypyrrole film was electrochemically grown on a 0.5-cm platinum electrode in a solution of 0.1 M tetraethylammonium tetrafluoroborate in acetonitrile [46]. The oxidation wave in the anodic sweep produced a reduction wave on the reverse cathodic sweep. Different diffusion processes involved most likely account for the different shapes of the oxidation and reduction waves. For example, when lithium perchlorate is the electrolytic salt, perchlorate anions diffuse into the polymer upon oxidation. However, upon reduction the more mobile lithium cations diffuse in... 

FIGURE 2 Cyclic voltammogram of a polypyrrole film (20 nm thick) grown on a platinum electrode in a 0.1 M tetraethylammonium tetrafluoroborate and acetonitrile solution. The scan rate was 100 mV per second. (From Ref. 4.)... 

Fig. 8. Cyclic voltammograms of a polypyrrole tetrafluoroborate film (20 run thick) on a platinum surface measured in 0.1 M tetraethylammonium tetrailuoroborate/acetonitrile solution (reprinted with permission from Ref.

See color insert.) (a) Graphene composite film with polypyrrole deposited for 120 sec. Inset shows SEM image at the observation area. White bar = 100 nm. (b) Cyclic voltammogram curves for pure graphene film, (c) Graphene with polypyrrole deposited for 120 sec in KCl solution between -0.4 and 0.6 V versus SCE at scan rates of 0.01, 0.02, 0.05, 0.1, and 0.2 V/sec. Source Davies, A. et al. 2011. Journal of Physical Chemistry C, 115,17612-17620. With permission.)... 

Fig. 20.12 Representative cyclic voltammograms as a function of scan rate for an electronically conductive polymer film, polypyrrole. The scan rate increases from bottom to top, and the dashed lines refer to the voltammogram for the bare (support) electrode (e.g., glassy carbon).

The spectroscopic measurement can be made in response to either a potential (or current) step or a potential sweep. Examples of the latter approach are contained in Fig. 20.28a and 20.28b for UV-vis and Raman scattering measurements on a polypyrrole film electrode in aqueous media [144]. The dAldtantX dIldt(A = optical absorbance, I = Raman scattered light intensity) derivative signals versus potential have the shapes of cyclic voltammograms with the important difference that the spectroscopic signals are species-selective. 

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