Cyclic conductive polymers

Although the mechanisms discussed above are still topics of debate, it is now firmly established that the electrodeposition of conducting polymers proceeds via some kind of nucleation and phase-growth mechanism, akin to the electrodeposition of metals.56,72-74 Both cyclic voltammetry and potential step techniques have been widely used to investigate these processes, and the electrochemical observations have been supported by various types of spectroscopy62,75-78 and microscopy.78-80... 

Figure 4 compares cyclic voltammograms for a redox polymer (poly-[Fe(5-amino-1,10-phenanthroline)3]3+/2+)91 and p-doping and undoping of a conducting polymer (polypyrrole).92 The voltammogram for the redox... 

Figure 4. (A) Cyclic voltammograms over a range of scan rates for a redox polymer (poly-[Fe 5-amino-1,10-phenanthrotme)3]3+/>)91 and (B) p-doping and undoping of a conducting polymer (polypyrrole) (B). [(A) Reprinted from X. Ren and P. O. Pickup, Strong dependence of the election hopping rate in poly-tris(5-amino-1,10-phenan-throline)iron(HI/II) on the nature of the counter-anion J. Electroanal. Chem. 365, 289-292,1994, with kind permission from Elsevier Sciences S.A.]...

The electrochemistry of a polymer-modified electrode is determined by a combination of thermodynamics and the kinetics of charge-transfer and transport processes. Thermodynamic aspects are highlighted by cyclic voltammetry, while kinetic aspects are best studied by other methods. These methods will be introduced here, with the emphasis on how they are used to measure the rates of electron and ion transport in conducting polymer films. Charge transport in electroactive films in general has recently been reviewed elsewhere.9,11... 

Although cyclic voltammetry in a variety of electrolyte systems, and with a variety of doped polymers, has shown strong effects due to ion transport, it has provided little understanding. In fact, one of the important uses of ion transport data from the techniques discussed in the preceding subsections is that they help to provide an understanding of the cyclic voltammetry behavior of conducting polymer films. Their importance will... 

The kinetics of charge transfer between metallic electrodes and conducting polymer films have proved to be difficult to investigate, and little reliable data exist. Charge-transfer limitations have been claimed in cyclic voltammetry, and Butler-Volmer kinetics have been used in a number of... 

The unusual cyclic voltammograms and responses to large-amplitude potential steps of a variety of conducting polymer films have prompted a number of groups to develop nucleation models for their oxidation. The key features that they have sought to explain are the peaks observed in anodic chronoamperometry (see Fig. 14), and the dependence of the anodic peak position on scan rate207 and the time spent in the undoped state.20 ... 

Electrochemical measurements on polyaniline (PANI) produce a picture of the charge storage mechanism of conducting polymers which differs fundamentally from that obtained using PTh or PPy. In the cyclic voltammetric experiment one observes at least two reversible waves in the potential range between —0.2 and -)-1.23 V vs SCE. Above -1-1.0 V the charging current tends to zero. Capacitive currents and overoxidation effects, as with PPy and PTh, do not occur The striking... 

The conducting polymers show a significant non-faradaic component of the electrochemical mechanism. The essential differences of faradaic and non-faradaic systems in equilibrium behavior, trends of galvanostatic charge - discharge curves and cyclic voltammograms have been shown, and criteria for the identification of these mechanisms are proposed [8],... 

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. 

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. 

Cyclic voltammetry of the conducting polymers allows assessment of the electrochemical activity of the films and the redox processes involved. The electrochemical... 

Cyclic voltammetry is also an ideal analytical tool for assessing the electrochemical stability of the polymer films. This is a fundamental requirement for any conducting polymer to be considered for long-term use in electrochemical devices. The use of ionic liquids for the electrochemical cycling of poly(aniline) has been reported to enhance lifetimes to over a million cycles [12], and significant improvements in the cycling stability of poly(pyrrole) have also been reported [32]. 

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