Voltammetry, electroactive polymers

Peerce, P. J., Bard, A. J. (1980). Polymer films on electrodes m. Digital simulation model for cyclic voltammetry of electroactive polymer film and electrochemistry of poly(vinylferrocene) on platinum. J Electroanal Chem 114, 89-115. 

Charge transfer in electroactive polymers is usually investigated by techniques such as cyclic voltammetry, spectroelectrochemistry, and AC impedance. Using these techniques, one can extract information such as standard potentials, number of electrons transferred, rates of charge transfer, and intermediates, if any, in the redox reaction. These techniques are explained in some detail in Appendix 11,... 

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. 

Linear potential sweep and cyclic voltammetry have been used extensively to examine the redox behavior of surface-deposited electroactive polymer films qualitatively. In this respect the technique can be classified as a form of electrochemical spectroscopy, since it delineates regons of redox activity, and provides an initial survey of overall electrochemical behavior of an electroactive polymer film as a function... 

In conclusion linear potential sweep and cyclic voltammetry can be used to obtain quantitative information on charge percolation in electroactive polymer films. However analysis is complex, and it may be preferable to use a simpler technique, such as potential or current step perturbation, to determine the transport parameters, as outlined in the preceding section. 

The normal pulse voltammetry (NPV) technique has been used largely by Oyama and coworkers to determine Z>cr values for charge percolation through the polymer and the kinetic parameters and a for charge injection at the support/film interface. The technique has been used quite extensively as a routine tool in electroanalytical chemistry, but surprisingly it has not been used extensively in the field of electroactive polymers. 

Piro B, Haccoun J, Pham MC, Tran LD, Rubin A, Perrot H, Gabiielli C (2005) Study of the DNA hybridization transduction behavior of a quinone-containing electroactive polymer by cyclic voltammetry and electrochemical impedance spectroscopy. J Electroanal Chem 557 155-165... 

Electrochemical polymerization offers particular advantages in that polymerized porphyrins can form electroactive, adherent and stable films on solid electrodes. Oxidative electropolymerization of several porphyrins and metalloporphyrins have been reported . Special focus has been placed on amino-substituted porphyrins due to the propensity of aniline to form electroactive polymers. Murray et al. reported on the electropolymerization of tetrakis(o-aminophenyl)porphyrin and several para-, ortho-, and meta-substituted tetrakis(aminophenyl)porphyrins with Co as a central metal s. They found that poly-Co(o-NH2)TPP films are effective catalysts for the electroreduction of oxygen in aqueous solution. Metalloporphyrin films on solid electrodes have been mainly characterized by voltammetry and resonsance Raman spectroscopy. The electrochemistry of ruthenium paradiethylamino substituted tetraphenylporphyrins recently have been investigated . This study reports the ac impedance and UV-visible reflectance spectroscopic studies of paradiethylamino substituted tetra-phenylporphyrin films formed via an oxidative electropolymerization process. 

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... 

A variety of other techniques have been used to investigate ion transport in conducting polymers. The concentrations of ions in the polymer or the solution phase have been monitored by a variety of in situ and ex situ techniques,8 such as radiotracer studies,188 X-ray photoelectron spectroscopy (XPS),189 potentiometry,154 and Rutherford backscatter-ing.190 The probe-beam deflection method, in which changes in the density of the solution close to the polymer surface are monitored, provides valuable data on transient ion transport.191 Rotating-disk voltammetry, using an electroactive probe ion, provides very direct and reliable data, but its utility is very limited.156,19 193 Scanning electrochemical microscopy has also been used.194... 

The concentration profile of fixed oxidized and reduced sites within the film depends on the dimensionless parameter Dcjr/d2, where r is the experimental timescale, i.e. RT/Fv in cyclic voltammetry, and d is the polymer layer thickness. When Dcix/d2 1, all electroactive sites within the film are in equilibrium with the electrode potential, and the surface-type behavior described previously is observed. In contrast, Dcjx/d2 <3C 1 when the oxidizing scan direction is switched before the reduced sites at the film s outer boundary are completely oxidized. The wave will exhibit distinctive diffusional tailing where these conditions prevail. At intermediate values of Dcjr/d2, an intermediate ip versus v dependence occurs, and a less pronounced diffusional tail appears. 

Electroactivity (electroactive or electrochemically active compounds) — The capability of a substance to take part in a faradaic electrode reaction. Electroactive compounds can be in the gaseous, liquid, or solid state or they may be dissolved in (liquid or solid) solutions. Various compounds are also electroactive in the adsorbed state (see -> adsorption, - adsorptive accumulation, -> adsorptive stripping voltammetry) or as polymer films (see -> polymer-modified electrodes) on electrodes. 

One of the most well-studied characteristics of the ferrocene nucleus is its ability to undergo a reversible one-electron oxidation (57). Polymers such as poly(vinylferrocene) possess electroactive ferrocenyl moieties which are well-separated from one another by insulating organic units. The ferrocenyl units in these polymers are essentially noninteracting, and a single reversible oxidation wave is detected by cyclic voltammetry (55). The observation that the poly(ferrocenylsilane) 15 (R = R = Me) exhib-... 

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