Semiconducting properties of polypyrrole films in aqueous solution |
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Authors: | Ursula Rammelt Sven Bischoff Mohamed El-Dessouki Renate Schulze Waldfried Plieth Lother Dunsch |
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Institution: | Dresden University of Technology, Department of Chemistry, Institute of Physical Chemistry and Electrochemistry, Mommsenstrasse 13, D-01062 Dresden, Germany, DE Institut für Festk?rper- und Werkstofforschung Helmholtzstrasse 20, D-01171 Dresden, Germany, DE
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Abstract: | The influence of the nature of the anions on the conductivity of polypyrrole films in aqueous solution was investigated by
photocurrent spectroscopy combined with electrochemical impedance spectroscopy in dependence on the potential. As demonstrated,
the conductivity of polypyrrole films at negative potentials can vary from a semiconducting to an ionic conducting state,
depending on the size of the charge-compensating counter-anion incorporated during the electropolymerization. The reduced
polypyrrole shows semiconducting properties when small anions are inserted, releasing the polymer matrix during the reduction
process. The polymer can than be considered as a two-layer system, consisting of a semiconducting layer and a porous layer.
Measurements at different thickness of polypyrrole films have shown that the position of the semiconducting layer is in the
electrode/polymer interface. The ohmic resistance of the semiconducting layer is in the range 1–5 kΩ, the capacitance approaches
a value of 100–500 nF and the flatband potential is −0.62 VSCE. If large anions are incorporated, cation insertion takes place during reduction, the electrolyte content in the polymer
then is relatively high and the polymer's behaviour is similar to that of an ionic conductor. The results are presented and
discussed together with the example of methylsulfonate as a relatively small anion and polystyrenesulfonate as a large anion.
Received: 28 July 1998 / Accepted: 22 February 1999 |
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Keywords: | Polypyrrole Anion influence Film thickness Photocurrent Impedance spectroscopy |
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