Cyclic voltammetry electronically conducting polymers

FIGURE 18.2 Typical cyclic voltammetry (CV) corresponding to redox switching of electronically conducting polymers (ECPs). 

Bilayer and trilayer actuators Characterizations of Electrochemical cell Experimental procedure Materials Conducting polymers (CPs) Liquid electrolyte Open air Cyclic voltammetry Dibutyltin dilaurate Electronic conducting polymers (ECPs) Interpenetrating polymer network (IPN) Poly (3,4-ethylenedioxythiophene) (PEDOT) Polypyrrole (PPY) Actuation mechanism of Electrogeneration of Electropolymerization of pyrrole monomer Oxidation and reduction reaction of Polyvinylidene fluoride (PVDF) Solid polymer electrolyte (SPE) membrane Force characterizations IPNs Load curves and metrics PVDF membrane Strain characterizations... 

Table 20.8 contains a compilation of literature entries on the voltammetry of conducting polymer films. The scope of these studies is similar to that of the transient experiments discussed in Section V.A in terms of the types of electrodes and media employed. Both cyclic and hydrodynamic voltammetry have been used as shown in Table 20.8. Other aspects under discussion include the mathematic modeling of cyclic voltammo-grams [277,278], the occurrence and origin of prewaves in the cyclic voltammograms [319], the use of very fast scan rates [220], structural relaxation effects and their manifestation in voltammetry [304,317,320], the inactivation of polymer electroactivity when driven to extreme potentials, and the so-called polythiophene paradox [225,226,306,321]. Unusual media and cryogenic temperatures have also been employed for the volta-mmetric observation of doping phenomena [322-325]. Dual-electrode voltammetry (Section II.1) has been performed on derivatized polypyrrole [290] in an attempt to deconvolute the electronic and ionic contributions to the overall conductivity of the sample as a function of electrode potential. Finally, voltammetry has been carried out in the solid state , i.e., in the absence of electrolyte solutions [215,323].

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... 

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. 

The direct synthesis by anodic oxidation of a new series of electrically conducting poljnners is described.. Our polymers derive from sulfur and/or nitrogen containing hetero-cycles such as 2-(2-thienyl)pyrrole, thiazole, indole, and phthalazine. The anodic oxidation of these monomers is carried out in acetonitrile solutions containing tetrabu-tylammonium salts (TBA X ) ith X = BF, tetraethylammonium salt, TEA H C-C H -S0. Characterization of the materials by electrical conductivity, electron spin resonance, uv-visible spectroscopy, and cyclic voltammetry is discussed. 

Methods of Characterization The polymers were characterized by four-probe electrical conductivity measurements between room temperature and liquid nitrogen, electron spin resonance (Varlan E-line series), scanning electron microscopy (Hitachi 520), cyclic voltammetry (Princeton Applied Research Instruments), and uv-vlsl-ble spectroscopy (Perkin Elmer 330). 

In all cases, the films were obtained by oxidative electropolymerization of the cited substituted complexes from organic or aqueous solutions. The mechanism of metalloporphyrin Him formation was suggested to be a radical-cation induced polymerization of the substituents on the periphery of the macrocycle. As it was reported for the case of polypyrrole-based materials ", cyclic voltammetry and UV-visible spectroscopy with optically transparent electrodes were extensively used to provide information on the polymeric films (electroactivity, photometric properties, chemical stability, conductivity, etc.). Based on the available data, it appears that the electrochemical polymerization of the substituted complexes leads to well-structured multilayer films. It also appears that the low conductivity of the formed films, combined with the cross-linking effects due to the steric hindrance induced by the macrocyclic Ugand, confers to these materials a certain number of limitations such as the limited continuous growth of the polymers due to the absence of electronic conductivity of the films. Indeed, the charge transport in many of these films acts only by electron-hopping process between porphyrin sites. 

Dian et al. [334] reported the electrochemical polymerization of 3-substituted and 3-,4-disubstituted selenophenes in acetonitrile saturated with lithium perchlorate. Two methods were used to study systematically the influence of the substituents on polymer formation cyclic voltammetry and chronoamperometry. The film formation process is greatly influenced by the electronic and steric effects of the substituents. For example, electron donating groups such as methyl and methoxy substituents appear to stabilize the radical cation intermediates, diminish the oxidation potential, and therefore allow polymer formation. The presence of halogen substituents raises the oxidation potential and does not lead to polymeric films. The conductivities of polyselenophene derivatives are quite low. For example, oxidized poly-3-methyl-selenophene and poly-3,4-dimethyl-selenophene have conductivities around 9 x 10 and 6 x 10" S cm", respectively. 

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