Polypyrrole dopant diffusion

Skotheim et al. [286, 357, 362] have performed in situ electrochemistry and XPS measurements using a solid polymer electrolyte (based on poly (ethylene oxide) (PEO) [363]), which provides a large window of electrochemical stability and overcomes many of the problems associated with UHV electrochemistrty. The use of PEO as an electrolyte has also been investigated by Prosperi et al. [364] who found slow diffusion of the dopant at room temperature as would be expected, and Watanabe et al. have also produced polypyrrole/solid polymer electrolyte composites [365], The electrochemistry of chemically prepared polypyrrole powders has also been investigated using carbon paste electrodes [356, 366] with similar results to those found for electrochemically-prepared material. 

Shinohara et al.52n suggested that the diffusion rate of dopant ions in polypyrrole films depends upon the size of the anion used as counter-ion in the electrochemical synthesis so that films prepared with CI counter-ions were impermeable to larger ions, at least in the time-scale of a cyclic voltammetry experiment. Tietje-Girault et al. 522) made two-layer polypyrrole films in which a layer was prepared with a large... 

In the case of polypyrrole, both of these situations have been reported. Obviously, then, the transport is optimized if it is dominated by only one diffusing species with a fast rate. In an attempt to ensure just this, a novel method was devised by the synthesis of a self-doped conducting polymer [60]. The key feature in this structure is the chemical anchoring of a dopant (anion) in the polymer chain itself, thus ensuring that cations are the mobile species during the redox process. Figure 4 shows the structure of the pyrrole-based polymer. 

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