COLOR IMPEDANCE SPECTROSCOPY OF POLYPYRROLE FILMS

Electrochemical impedance spectroscopy and color impedance (electromodulated optical transmittance) spectroscopy have been employed to investigate the redox dynamics of polypyrrole films. Results for the films in their slightly oxidized state (- 0.3 V/SCE) are presented. The electrical response and the optical response at 780 nm were identical, being composed of a fast and a slow process, whereas the response at 410 nm comprised only the fast process. These frequency responses have been modeled with an equivalent circuit taking into account three charge transport paths within the films. The fit to the data based on this model was fairly good. These results indicate that the redox reaction between bipolaronic and polaronic species is accompanied by fast and slow charge transport processes, while that between polaronic and neutral species is accompanied by the fast process only. A new model for the redox dynamics and charge transport in the films is presented.