Polypyrrole electrochemical

Polythiophenes are in general more hydrophobic materials that polypyrroles. Electrochemical switching is not so efficient in aqueous media. Therefore, some workers have used the ability to attach functional groups such as polyethers148 to increase hydrophilicity and improve electrochemical behavior in aqueous solutions. 

Polypyrrole electrochemically polymerized within a matrix resin electrically conducting material with improved mechanical properties over those of PPy Lindsey Street, 1985... 

An, K.H., et al. 2002. High-capacitance supercapacitor using a nanocomposite electrode of single-walled carbon nanotube and polypyrrole. / Electrochem Soc 149 (8) A1058. 

Mesopores Polypyrrole Electrochemical Improve electrical contact, gas sensing Moreno et al. (1999), Vikoslav et al. (2006)... 

Qian, R., Qiu, J., and Shen, D., Conducting polypyrrole electrochemically prepared from aqueous solutions. Synth. Met., 18, 13-18 (1987). 

The first conducting PHC produced electrochemi-cally was polypyrrole [4,5], and most PHCs are produced in this way. The reason is that polymerization may be controlled instrumentally and the polymer is obtained as film suitable for further electrochemical modifications. Thus electrochemistry plays the dual role of a synthetic and an analytical tool. After polypyrrole electrochemical polymerization was rapidly... 

Xue, S. and G. Yin, Proton exchange membranes based on modified sulfonated poly(ether ether ketone) membranes with chemically in situ polymerized polypyrrole , Electrochem. Acta, 52 (2006) 847-853. 

Figure 2. Gas sensor consisting of doped polypyrrole electrochemically polymerised on to interdlgltated gold electrodes screen-printed on an alumina substrate.

Nevertheless, the approach has been successfully demonstrated to interpret assay data for two representative electrode types fabricated with different immobilization methods (i) direct physical adsorption to a carbon felt electrode, and (ii) enzyme immobilized within polypyrrole electrochemically deposited on a stainless steel mesh. In each case, the data were used to estimate both V ax and the cumulative mass transfer parameter M (Table 12.1). 

Electrochemical synthesis of molecular-interfaced FDH on Pt electrode The mol ecul ar-i nterf aced FDH was electrochemical 1y prepared on the Pt electrode surface by the following two steps potential-control 1ed adsorption of FDH, and (2) electrochemical polymerization of polypyrrole.Electrochemical adsorption of FDH (EC 1.1.99.11, MW 141,000) from G1 uconobacter sp. on... 

Functionalized conducting monomers can be deposited on electrode surfaces aiming for covalent attachment or entrapment of sensor components. Electrically conductive polymers (qv), eg, polypyrrole, polyaniline [25233-30-17, and polythiophene/23 2JJ-J4-j5y, can be formed at the anode by electrochemical polymerization. For integration of bioselective compounds or redox polymers into conductive polymers, functionalization of conductive polymer films, whether before or after polymerization, is essential. In Figure 7, a schematic representation of an amperomethc biosensor where the enzyme is covalendy bound to a functionalized conductive polymer, eg, P-amino (polypyrrole) or poly[A/-(4-aminophenyl)-2,2 -dithienyl]pyrrole, is shown. Entrapment of ferrocene-modified GOD within polypyrrole is shown in Figure 7. 

Fig. 5. Evolution of optical spectra of polypyrrole during electrochemical doping.

Although polyacetylene has served as an excellent prototype for understanding the chemistry and physics of electrical conductivity in organic polymers, its instabiUty in both the neutral and doped forms precludes any useful appHcation. In contrast to poly acetylene, both polyaniline and polypyrrole are significantly more stable as electrical conductors. When addressing polymer stabiUty it is necessary to know the environmental conditions to which it will be exposed these conditions can vary quite widely. For example, many of the electrode appHcations require long-term chemical and electrochemical stabihty at room temperature while the polymer is immersed in electrolyte. Aerospace appHcations, on the other hand, can have quite severe stabiHty restrictions with testing carried out at elevated temperatures and humidities. 

Entrapment of biochemically reactive molecules into conductive polymer substrates is being used to develop electrochemical biosensors (212). This has proven especially useful for the incorporation of enzymes that retain their specific chemical reactivity. Electropolymerization of pyrrole in an aqueous solution containing glucose oxidase (GO) leads to a polypyrrole in which the GO enzyme is co-deposited with the polymer. These polymer-entrapped GO electrodes have been used as glucose sensors. A direct relationship is seen between the electrode response and the glucose concentration in the solution which was analyzed with a typical measurement taking between 20 to 40 s. 

Polypyrrole, poly thiophene, polyfuran, polycarbazole, polystyrene with tetrathi-afulvalene substituents, polyethylene with carbazole substituents, and poly-oxyphenazine as electrochemically active polymers for rechargeable batteries 97CRV207. 

Komori and Nonaka132,133 electrochemically oxidized methyl, isopropyl, n-butyl, isobutyl, r-butyl and cyclohexyl phenyl sulfides (108) and cyclohexyl p-tolyl sulfide (109) to their sulfoxides using a variety of polyamino acid-coated electrodes to obtain the range of e.e. values shown in parentheses. The highest enantiomeric purities were obtained using an electrode doubly coated with polypyrrole and poly(L-valine), an electrode which also proved the most durable of those prepared. 

Very low asymmetric induction (e.e. 0.3-2.5%) was noted when unsymmetrical sulphides were electrochemically oxidized on an anode modified by treatment with (— )camphoric anhydride or (S)-phenylalanine methyl ester299. Much better results were obtained with the poly(L-valine) coated platinum electrodes300. For example, t-butyl phenyl sulphide was converted to the corresponding sulphoxide with e.e. as high as 93%, when electrode coated with polypyrrole and poly(L-valine) was used. 

Several alkyl aryl sulfides were electrochemically oxidized into the corresponding chiral sulfoxides using poly(amino acid)-coated electrodes448. Although the levels of enan-tioselection were quite variable, the best result involved t-butyl phenyl sulfoxide which was formed in 93% e.e. on a platinum electrode doubly coated with polypyrrole and poly(L-valine). Cyclodextrin-mediated m-chloroperbenzoic acid oxidation of sulfides proceeds with modest enantioselectivity44b. 

Sodium dodecyl sulfate has been used to modify polypyrrole film electrodes. Electrodes synthesized in the presence of sodium dodecyl sulfate have improved redox processes which are faster and more reversible than those prepared without this surfactant. The electrochemical behavior of these electrodes was investigated by cyclic voltametry and frequence response analysis. The electrodes used in lithium/organic electrolyte batteries show improved performance [195]. 

Here we introduce a personal point of view about the interactions between conducting polymers and electrochemistry their synthesis, electrochemical properties, and electrochemical applications. Conducting polymers are new materials that were developed in the late 1970s as intrinsically electronic conductors at the molecular level. Ideal monodimensional chains of poly acetylene, polypyrrole, polythiophene, etc. can be seen in Fig. 1. One of the most fascinating aspects of these polymeric... 

When polypyrrole was electrogenerated from dry acetonitrile electrolytes, a black polymer grew and adhered to the electrode. After a few seconds of electropolymerization, a black cloud was observed around the electrode. The film obtained had poor electrochemical and physical properties. Increasing the water content to 2% (w/w) gives, at 800 mV, films with improved properties. The black cloud around the electrode disappears. 

Polypyrrole relatives obtained by electrosynthesis in the presence of different small inorganic or organic counter-ions that are interchanged with the electrolyte during electrochemical control of the material. 

This reverse electrochemical control of the gel composition and volume is the basis for the singular electrochemical properties and the concomitant applications of conducting polymers. Reactions and properties based on polypyrrole films can be summarized as shown in Table 5 and below ... 

The flow of an anodic current oxidizes the conducting polymer and the film swells. At the polypyrrole/tape interface, electrochemically stimulated conformational changes in the polymer promote an expansion that... 

Figure 35. Schematic representation of the reversible variation of volume associated with the electrochemical switching of polypyrrole. Changes in free volume are mainly due to two effects electrostatic repulsions between fixed positive charges and exchange of cations, anions, and solvent molecules between the polymer and the solution. (Reprinted from T. F. Otero, H.-J. Grande, and J. Rodriguez, J. Phys. Chem. 101, 3688, 1997, Figs. 1, 3,6, 7, 13. Copyright 1997. Reprinted with the permission of the American Chemical Society.)...

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