Polypyrrole films

The poor stability on exposure to air and water, particularly at elevated temperatures, which results in a reduction in conductivity, also poses problems. In the case of polypyrrole it has been found that conductivity can, however, be maintained either by the drastic measure of storing under the protective layer of the inert gas argon or embedding polypyrrole film in a matrix of an epoxide resin-glass-fibre composite. 

Describe clearly why the oxidation of polypyrrole film results in the uptake of an anion from the surrounding solution. 

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]. 

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 ... 

Figure 19. (1) Oxidized polypyrrole (PPy) film electrogenented on a steel electrode. (2) A tape was fastened to the dry polypyrrole film (A). B is doublesided tape and C is a protective sheet of paper. (3) The bilayer device with a protective film is removed from the electrode. (4) The protective sheet is peeled off and the bilayer is ready to work. (Reprinted from Handbook of Organic Conductive Molecules ami Polymers, H.S. Nalwa, ed.,Vol. 4,1997, Figs. 10.13, 10.15a, 10.18, 10.36. Reproduced with permission of John Wiley Sons, Ltd., Chichester. UK.)...

At dusk the window becomes lighter. When the polypyrrole film is completely reduced and the oxide is fully oxidized and darkening continues, the current of the photocell decreases at it and the electric light in the room is switched on. The intensity of the electric current sent to the lamp is increased in such a way that the luminosity in the room remains constant at all times. In cars or for other applications, the device can work automatically or by hand, darkening all the windows when the car is parked on a sunny day. 

Figure 38. Evolution of the proposed surface aspect of a polypyrrole film during an oxidation reaction initiated from high cathodic potentials (E < -800 mV vs. SCE). The chronoamperometric response is shown at the bottom. Experimental confirmation can be seen in the pictures in Ref. 177. (Reprinted from T. F. Otero and E. Angulo, Oxidation-reduction of polypyrrole films. Kinetics, structural model, and applications. Solid State Ionics 63-64, 803, 1993, Figs. 1-3. Copyright 1993. Reprinted with kind permission of Elsevier Science-NL, Sara Burgerhartstraat 25, 1055, KV Amsterdam, The Netherlands.)...

Figure 50. Semilogarithmic plot of cathodic (Ec) and anodic (E) potentials against values of 1 IQ [cPQityd ] extracted from Figs. 52 and 53. Following Eq. (48), values of the coefficient of electrochemical relaxation (zr) and the coefficient of cathodic polarization (ze) can be deduced from the slopes. (Reprinted from T. F. Otero and H.-J. Grande, Reversible 2D to 3D electrode transition in polypyrrole films. ColloidSurf. A. 134,85, 1998, Figs. 4-9. Copyright 1998. Reproduced with kind permission of Elsevier Science-NL, Sara Burgerhartstraat 25, 1055 Amsterdam, The Netherlands.)...

Figure 56. Plot of (a) 1 -1) N/tf% vs. t)c and (b) tjN vs. tjc for polypyrrole films submitted to potential sweeps, from which the nucleation parameters (z and / ) can be obtained. (Reprinted from T. F. Otero, H.-J. Grande, andJ. Rodriguez, J. Phys. Chem. 101,8525,1997, Figs. 3-11, 13. Copyright 1997. Reproduced with permission from the American Chemical Society.)...

Figure 15. Complex plane impedance plots for polypyrrole at (A) 0.1, (B) -0.1, (C) -0.2, (D) -0.3, and (E) -0.4 V vs. Ag/AgCl in NaCl04(aq). The circled points are for a bare Pt electrode. Frequencies of selected points are marked in hertz. (Reprinted from X. Ren and P. O. Pickup, Impedance measurements of ionic conductivity as a probe of structure in electrochemi-cally deposited polypyrrole films, / Electmanal Chem. 396, 359-364, 1995, with kind permission from Elsevier Sciences S.A.)...

The value of the EQCM is exemplified by the data shown in Fig. 17.177 The first reduction of the polypyrrole film was initially accompanied by a mass decrease, as expected for anion expulsion according to Eq. (1). However, after the reduction was ca. 75% complete, the mass began to increase, indicating a switch of the charge neutralization mechanism to cation insertion [Eq. (5)]. 

Figure 17. Plots of (a) current end (b) change in mass vs. potential for a polypyrrole film in propylene carbonate containing 0.1 M UCIO ...

Otero and co-workers208,212 have visually observed nuclei of oxidized polymer in thin polypyrrole films on electrodes. They attribute these to sites of counter-ion and solvent ingress. A nucleation model based on the growth of ionically conductive zones provides good agreement with experimental chronoamperometric responses. 

Figure 21. Cyclic voltammograms (at 20to lOOmVs-1)of [FefCNJd3"74-electrostatically trapped in polypyrrole films with an alkyl pyridinium substituent at the (A) 1 - or (B) 3-position.243 (Reprinted with permission from J. Phys. Chem. 96, 5604-5610, 1992 Copyright 1992, American Chemical Society.)...

Cyclic voltammetric studies involving polymers, 558 and the nature of charge carriers, 561 and the nucleation loop, 557 of poly (3-methylthiophene), 564 and parallel-band electrodes, 570 Cyclic voltammograms as a function of scan rate, 559 involving polymerization, 559 with polyanaline, 566 of polypyrrole film, 581... 

Simultaneous ESR and electrochemical measurements on a polypyrrole film give convincing evidence that the charging process in this film involves the generation of paramagnetic species which are obviously intermediates in the process of switching from the neutral to the oxidized state In any case, independent of all other findings,... 

In 1979, the formation of conductive polypyrrole films by the electrochemical oxidation of pyrrole was reported for the first time This work has stimulated intense and fruitful research in the field of organic conducting polymers. Further important conductive polymers are polythiophene, polyaniline and polyparaphenylene. The development and technological aspects of this expanding research area is covered... 

Table 1. N-substituted pyrroles employed in the preparation of redox-Modified polypyrrole films on electrodes...

Further interesting redox modified polypyrrole films were prepared e.g. a polymeric copper phenanthroline complex that can be reversibly de- and re-metallated because it retains the pseudotetrahedral environment after decomple-xation, A very diversified electrochemistry is displayed by polypyrrole films containing electron donor as well as electron acceptor redox centers in the same film... 

Diaz AF, Logan JA(1980)Electroactive polyanihne films. JElectroanalChem 111 111-114 Noufi R, Nozik AJ, White J, Warren LF (1982) Enhanced stability of photoelectrodes with electrogenerated polyanUine films. J Electrochem Soc 129 2261-2265 Noufi R, Tench D, Warren LE (1981) Protection of semiconductor photoanodes with photoelectrochemicaUy generated polypyrrole films. J Electrochem Soc 128 2596-2599 Jaeger CD, Fan FRF, Bard AJ (1980) Semiconductor electrodes. 26. Spectral sensitization of semiconductors with phthalocyanine. J Am Chem Soc 102 2592-2598 Gerischer H (1977) On the stability of semiconductor electrodes against photodecomposition. J Electroanal Chem 82 133-143... 

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