CHRONOPOTENTIOMETRIC STUDIES OF POLYANILINE FILMS

Electrochemically prepared polyaniline (PANI) films have been studied by galvanostatic charge injection. The potentiostatic-galvanostatic-potentiostatic (PGP) technique was used to ensure that the initial oxidation state of the polymer was well defined. The potential of the PANI film was recorded during the injection and removal of charge as well as during the subsequent relaxation under open-circuit (zero-current) conditions. The chronopotentiometric responses observed during the first oxidation step exhibit an overpotential maximum at short times and this is interpreted as evidence for the nucleation and growth of conducting regions in the polymer. By contrast, the chronopotentiometric responses recorded during reduction of the conducting emeraldine form show no such effect. The open-circuit potential-charge relationships recorded during oxidation and reduction do not coincide, mainly since the oxidation responses deviate strongly from equilibrium behaviour. The difference between oxidation and reduction is also demonstrated by the fact that the potential relaxes substantially at open-circuit when the oxidation current is interrupted, whereas the open-circuit potential remains almost constant after a cathodic current pulse. It is concluded that oxidation and reduction must proceed by different pathways and involve different degrees of disorder.