Impedance spectroscopy of polypyrrole/poly(styrenesulphonate) composites. Simultaneous anion and cation transport

Abstract

Anodic oxidation of pyrrole in a solution containing both sodium perchlorate and sodium poly(styrenesulphonate) (NaPSS) forms polypyrrole (PPY) that is doped partially with ClO 4 − and partially with PSS. The impedance of PPY/PSS/ClO 4 film coated Pt electrodes in 0.2 M NaClO 4(aq) shows simultaneously the ion transport behaviours of PPY/ClO 4 and PPY/PPS. The fully oxidized form contains ClO − 4 as the major mobile ionic species, and therefore its ionic conductivity decreases with decreasing electrode potential as ClO − 4 ions are expelled. The reduced form contains Na + as the major mobile ionic species. Increasing the potential causes expulsion of these cations, and therefore decreases the film's ionic conductivity. At intermediate oxidation states, both mobile anions and cations are present and contribute to the film's ionic conductivity. Complex impedance plots, capacitance plots and cyclic voltammograms show the separation of two charging processes, indicating that the PSS and ClO 4 − doped parts of the polymer occur as separate domains. The observed impedance responses can be modelled with an electrical circuit containing two parallel transmission lines, representing anion and cation transport, respectively. At low frequencies, both experimental and simulated complex plane impedance plots show a deviation from the ideal capacitive response of a simple transmission line.