Electrodeposition of Conductive Polymers

Conductive polymers may be synthesized via either chemical or electrochemical polymerization methods. Electrodeposition of conductive polymers from electrolytes is, thus, feasible provided that the depositing polymer is not soluble in the electrolyte.206 Conductive polymers can be deposited from the electrolytes containing the monomers via either electrooxidation or electroreduction, based on the monomer type used. Similar to that of metals, the electrodeposition of polymers is based on nucleation and growth. The deposition mechanism involves oxidation of monomers adsorbed on the electrode surface, diffusion of the oxidized monomers and oligomerization, formation of clusters, and eventually film growth.213 

Despite the limited improvements in material development for supercapacitor electrodes, the specific capacitance and life cycle of the newly developed materials cannot be compared with those of Ru02. 

Electrodeposition is a unique, versatile technique for fabrication of metal oxide, polymer, and composite electrodes for electrochemical supercapacitors. Composition, crystal structure, and morphology of the deposits can be easily manipulated by adjusting the electrodeposition parameters to achieve improved capacitive behavior. Current progress, however, is far from the commercial expectations for electrochemical supercapacitors. 

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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... 

The reproducibility of the electrodeposition of conducting polymer films has been a very difficult issue. It has long been realized that each laboratory produces a different material and that results from different laboratories are not directly comparable.82 We have experienced reproducibility problems with almost all of the electrochemically polymerized materials used in our work. 

Oxide, flouride, and polymeric films, as well as certain others, are used as protective coatings for HTSC materials (for example, see [505]). The electrodeposition of conducting polymers such as polypyrrole [433,491, 493, 506], polythiophene and its derivatives [493, 507], and polyaniline [478] is the most effective process. Anodic electropolymerization in acetonitrile solutions proceeds without any degradation of the HTSC substrate and ensures continuous and uniform coatings. Apparently, this method is promising not only for the fabrication of compositions with special properties based on HTSC [50, 28,295] as mentioned above, but also for the creation of junctions with special characteristics [507]. 

Undoubtedly, electrodeposition of conducting polymers on iron is the process most studied. The first PPy coating of iron in aqueous media was carried out by Schirmeisen and Beck [85] in the presence of nitrate salts, then, by Lacaze etal. [12,13] who improved the process and achieved good protection after the iron surface had been pretreated by dilute nitric acid in order to improve the adhesion [86,87]. Just as in the nitrate process, this procedure provided a passivation of iron, but also involved an increase of the roughness of the surface resulting from a slight attack on the surface by the acid, the effect of which was to improve the mechanical adherence [88]. 

Electrodeposition of conducting polymers on copper has been investigated by several groups, and various salts have been tested to achieve the electrochemical polymerization of pyrrole from aqueous solutions in a one-step process. No serious difficulty was found, and electrolytes used previously on iron, such as oxalic acid [115,116], salicylates [117,118], and tartrate [119] were found suitable for PPy electrodeposition on copper and its alloys aqueous phosphate solutions were also found to provide highly adherent and homogenous films [120]. In all cases, PPy electrodeposition occurred after the preliminary passivation of copper through a mixed copper salt, copper oxide, or copper hydroxide layer. A two-step process, where an oxalate-doped PPy underlayer (PPy-Oxalate) is first deposited, followed by a dodecylbenzenesulfonate-doped PPy layer... 

DJi. Tallman, M.P. Dewald, C.K. Vang, G.G. Wallace, and G.P. Bierwagen, Electrodeposition of conducting polymers on active metals hy electron transfer mediation. Current Applied Physics, 4, 137 140 (2004). 

Functionalized Solvent-Processable Polymers Conducting Polymer Composites and Blends Electrodeposition of Conducting Polymers... 

In contrast, the electrodeposition of conducting polymers is an anodic process that involves both polymerization and subsequent deposition of the polymer. It is most often carried out at noble metal electrodes such as gold or platinum, or sometimes at carbon electrodes, using potentiostatic, potentio-dynamic, or galvanostatic methods [19]. These electrochemical methods provide accurate control over the polymerization rate, localizes the polymerization reaction at the metal surface to be covered, and permits precise control of polymer film thickness. 

The electrodeposition of conducting polymer from a solution phase is a transformation reaction. The usual cooperative processes (solid -o- liquid, liquid <-> vapour, solid vapour) which possess a latent heat of transition and present a discontinuous volumic modification are called first-order transitions. The absence of any latent heat and density variations and the presence of a discontinuity in the heat capacity-temperature curve are of second-order transitions. 

Electrodeposition of conducting polymers is a polynucleation and transients are triggered by a single potential step. Nucleation is independent of size and shape of electrode and the polynucleation curve always starts in synchronism with the potential step and is illustrated in Figure 12.9. 

Fig. II. 1.1). Other complex reaction schemes of practical importance commonly encountered involve association reactions such as precipitation or polymerisation. These processes may also be described by a series of consecutive reaction steps. However, as a further complication in these classes of reactions, the properties of the surface of the electrode may change during the course of the process. Extensive studies aimed at elucidating very complex reaction pathways have been conducted for the electrodeposition of conducting polymers and, as might be expected, fast scan rate cyclic voltammetry has made an important contribution to an understanding of the mechanism [114]. 

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