Conducting polymers electrodeposition

Recent developments on metal, metal oxide, and conductive polymer electrodeposition for energy device applications... 

In Chapter 3, by Shaigan, electrodeposition for electrochemical conversion and storage devices is presented. This chapter discusses the latest developments on metal, metal oxide, and conductive polymer electrodeposition processes developed and studied for the applications in the fields of fuel cells, batteries, and capacitors. The importance of electrodeposited materials, which are used or may have the future potential applications in the energy conversion or storage, is clearly shown. 

Electrochemical polymerization is a fast and simple, widely used method to synthesize different conducting polymers. Electrodeposition enables film formation on surfaces with complicated patterns as well as control of film thickness [5]. Furthermore, the subsequent growth of the polymer film and the charging reactions can be followed in situ [6]. Parameters such as solvent media, electrolyte, electrochemical method used for polymerization and monomer material, all have a profound effect on film morphology, charge transfer and transport properties. Different from the powdery products prepared through chemical approaches, this method enables an easy one-step deposition of the film directly at the surface of the electrode substrate that can be further applied for electrochemical purposes. 

One can also mention the case of composites-based conducting polymers electrodeposited and characterized on anodes of platinum- or carbon black- filled polypropylene from a stirred electrolyte with dispersed copper phthalocyanine. The electrolytic solution contained, besides the solvent (water or acetonitrile), the monomer (pyrrole or thiophene) and a supporting electrolyte. Patterned thin films were obtained from phthalocyanine derivatives, as reported in the case of (2,3,9,10,16,17,23,24-oktakis((2-benzyloxy)ethoxy)phthalocyaninato) copper . Such films were prepared by means of capillary flow of chloroform solutions into micrometer-dimension hydrophobic/hydrophilic channels initially created by a combination of microcontact printing of octadecylmercaptan (Cig-SH) layers on gold electrodes. These latter gave birth to a hydrophobic channel bottom while oxidative electropolymerization of w-aminophenol (at pH 4) led to hydrophilic channel walls. 

Conducting polymer composites have also been formed by co-electrodeposition of matrix polymer during electrochemical polymerization. Because both components of the composite are deposited simultaneously, a homogenous film is obtained. This technique has been utilized for both neutral thermoplastics such as poly(vinyl chloride) (159), as well as for a large variety of polyelectrolytes (64—68, 159—165). When the matrix polymer is a polyelectrolyte, it serves as the dopant species for the conducting polymer, so there is an intimate mixing of the polymer chains and the system can be appropriately termed a molecular composite. 

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. 

Tang, Y., et al., One-step electrodeposition to layer-by-layer graphene-conducting-polymer hybrid films. Macromolecular Rapid Communications, 2012. 33(20) p.1780-1786. 

An electronic conductive polymer was found by Strike al. as a support for platinum with a co-catalysts. The platinum particles were deposited on electrodeposited polypyrrole. 

The electrodeposition voltage is specific for any given electropolymerisation process. The polymers are obtained directly in the oxidised conducting form. Consequently, upon applied polarisation, polymerisation takes place, the p-doping of the polymer occurs and, finally, a film of the selected conductive polymer is deposited on the substrate. 

Fig. 11.8. Current density as a function of rotation rate during growth of electrodeposited polypyrrole film at 0.550 ( ), 0.600 ( ), 0.650 (T), and 0.700 ( ) V. (Reprinted with permission from D. J. Fermin, M. Mostany, and B. Scharifker, Electronically Conducting Polymers Synthesis and Electrochemical Properties of Polypyrrole, Curr. Topics Electrochem. 2 132-136, 1993.)...

Poly(3,4-ethylenedioxythiophene) (PEDOT) is a particularly popular conducting polymer as it can have good conductivity and stability and has a low band gap, which is pertinent to its use in photovoltaic devices. A number of authors have now studied the electrochemical synthesis of this polymer in different ionic liquids. Lu et al. [77] first demonstrated the use of [C4mim][BF4] to electrodeposit PEDOT onto ITO, and its application in an electrochromic numeric display. 

In Chapter 1 we explain the motivation and basic concepts of electrodeposition from ionic liquids. In Chapter 2 an introduction to the principles of ionic liquids synthesis is provided as background for those who may be using these materials for the first time. While most of the ionic liquids discussed in this book are available from commercial sources it is important that the reader is aware of the synthetic methods so that impurity issues are clearly understood. Nonetheless, since a comprehensive summary is beyond the scope of this book the reader is referred for more details to the second edition of Ionic Liquids in Synthesis, edited by Peter Wasserscheid and Tom Welton. Chapter 3 summarizes the physical properties of ionic liquids, and in Chapter 4 selected electrodeposition results are presented. Chapter 4 also highlights some of the troublesome aspects of ionic liquid use. One might expect that with a decomposition potential down to -3 V vs. NHE all available elements could be deposited unfortunately, the situation is not as simple as that and the deposition of tantalum is discussed as an example of the issues. In Chapters 5 to 7 the electrodeposition of alloys is reviewed, together with the deposition of semiconductors and conducting polymers. The deposition of conducting polymers... 

Electrochemistry in RTILs has recently been reviewed, and a book has been published on the topic. a large number of metals have been deposited from ionic liquids (Table 6.5) and a book has also been published on electrodeposition from these media. Alloys, semiconductors and conducting polymers have also been deposited from ionic liquids. The key advantages of ionic liquids for electrodeposition and electrochemical applications are their wide potential window, the high solubility of metal salts, the avoidance of water and their high conductivity compared to non-aqueous solvents. There are numerous parameters that can be varied to alter the deposition characteristics including temperature, the cation and anion used, diluents and additional electrolytes. ... 

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]. 

Different electron-conducting polymers (polyaniline, polypyrrole, polythiophene) are considered as convenient substrates for the electrodeposition of highly dispersed metal electrocatalysts. The preparation and the characterization of electronconducting polymers modified by noble metal nanoparticles are first discussed. Then, their catalytic activities are presented for many important electrochemical reactions related to fuel cells oxygen reduction, hydrogen oxidation, oxidation of Cl molecules (formic acid, formaldehyde, methanol, carbon monoxide), and electrooxidation of alcohols and polyols. 

Polypyrrole was often used as support for platinum particles. Similarly to the case of polyaniline, the activity of such electrodes for the oxidation of methanol depends both on the amount of platinum and on the thickness of the polymer film [43]. In the same study, by using in-situ infrared spectroscopy, it was confirmed that linearly adsorbed CO species are the only detectable species present at the electrode surface. The authors attributed the enhancement of the overall activity observed to the high and uniform dispersion of the metallic particles with, possibly, an effect of the conducting polymer matrix itself. The same conclusions were drawn from another study [44] where the size of the particles obtained by electrodeposition was estimated at 10 nm. In this study, the Pt particles were entrapped into the polymer layer and showed a better activity than particles only deposited on the polymer surface. The authors interpreted their results as a decrease of the poisoning phenomenon in the 3D film in comparison to the only 2D deposit. 

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