Capacitance of the polypyrrole/polyimide composite by electrochemical impedance spectroscopy

Electrically conducting polymers and their composites attract a lot of attention because of their high charge storage ability. As was shown previously, the composite of polypyrrole (PPy) and polyimide (PI) possesses better charge storage properties then pure PPy. Probably the PI matrix protects PPy from oxidative destruction and serves as a high molecular weight dopant. In this paper, the PPy/PI composite was studied by as electrochemical impedance spectroscopy at different applied dc polarization potentials. The properties of the coatings were found to differ significantly between pure PI and the PPy/PI composite, depending on the applied potential and on the amount of the conducting polymer. An additional time constant related to the PPy/PI interface appears when PPy is added to PI. The pseudocapacitance of the PPy/PI composite increased significantly with increased cathodic potential. This was explained by additional doping of PPy by the PI matrix.