Polypyrrole film perchlorate electrolyte

In the course of original investigations, Pyo et al. investigated the effect of pH, rather than that of an electrochemical procedure, on the ion transport at the perchlorate-doped polypyrrole film/electrolytic solution interface [150]. Preliminary EC-AFM investigations allowed them to detect a 12.6% volume increase when the solution pH varied from 1.0 to 11.3 in a 50 mM NaC104 aqueous solution. 

Figure 11.18 Impedance data measured for polypyrrole as function of the potential. The polymer film was prepared by anodic oxidation in a perchlorate electrolyte. Bode representation (A) impedance versus frequency and (B) phase angle versus frequency.

A typical cyclic voltammogram is shown in Fig. 2 for a polypyrrole film. The polypyrrole film was electrochemically grown on a 0.5-cm platinum electrode in a solution of 0.1 M tetraethylammonium tetrafluoroborate in acetonitrile [46]. The oxidation wave in the anodic sweep produced a reduction wave on the reverse cathodic sweep. Different diffusion processes involved most likely account for the different shapes of the oxidation and reduction waves. For example, when lithium perchlorate is the electrolytic salt, perchlorate anions diffuse into the polymer upon oxidation. However, upon reduction the more mobile lithium cations diffuse in... 

A battery cell where both the electrodes consist of dopable polymer is shown in Figure 5.23. The electrolyte in this case consists of Li+ClO 4 dissolved in an inert organic solvent, usually tetrahydro-furan or propylene carbonate. When two sheets of polyacetylene or PPP are separated by an insulating film of polycarbonate saturated in an electrolyte (lithium perchlorate), and completely encapsulated in a plastic casing, a plastic battery can be made. The two sheets of polyacetylene or PPP act as both anode and cathode for the battery. A schematic is shown in Figure 5.24. Although doped polyacetylene and polyaniline electrodes have been developed, polypyrrole-salt films are the most promising for practical appKcation. 

Eaves et al. [122] synthesized a redox-active thin film of ferrocene that was covalently attached to polypyrrole (Fig. 3). The inclusion of redox centers in the film was readily achieved by functionalizing the pyrrole nitrogen with the molecular electroactive species. The conductivities were typically 10 to 10 S cm . Golden yellow films were grown in acetonitrile with either O.l M tetrabutylam-monium perchlorate or tetrabutylammonium tetrafluoroborate added as the electrolytic salt. The films exhibited some rectifying behavior, which eventually decayed. The films could also be copolymerized with N-methylpyrrole. 

V versus 1.65 V for thiophene) may be substituted for thiophene and copolymerized with pyrrole. A mixture of approximately 90% pyrrole and 10% terthiophene in an electrolyte of 0.1 M tetraethylammonium perchlorate in acetonitrile produced pyrrole-like films. A redox potential in between that of the homopolymers was observed. The conductivity (1 S cm" ) of the film has a value that lies between typical values for polypyrrole (o- = 10 -10 S cm" ) and polythiophene produced electrochemically from terthiophene (o- = 10" -10" S cm" ). Furthermore, x-ray photoelectron spectra showed the presence of sulfur and nitrogen and indicated a stoichiometry of six pyrroles per thiophene unit. 

Polythiophene is readily produced by inserting a working electrode, counterelectrode, and reference electrode into a nonaqueous electrolyte in which 0.1 to 1.0 M thiophene is dissolved and then increasing the cell potential to greater than 1.6 V (versus SCE). Salts such as lithium or tetrabutylammonium perchlorate, hexafluo-rophosphate, or trifluoromethylsulfonate are typical electrolytes. Acetonitrile, ben-zonitrile, dichloromethane, and tetrahydrofuran are suitable solvents. As previously discussed for polypyrrole, polythiophene has been prepared in aqueous solutions [247]. A conductive, electroactive poly thiophene film was polymerized from a phosphoric acid-water-thiophene system using mild electrochemical polymerization conditions. 

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