Wide pH range microelectrode study of the electrochemical behaviour of polyaniline films in buffered solutions

Abstract

The electrochemistry of polyaniline (PANI) films deposited on platinum microelectrodes has been studied in a wide pH region, at constant ionic strength. Cyclic voltammograms, recorded at a sweep rate of 100 V s–1 indicate that the films remain electroactive at pH values as high as 9 provided that the films are only switched between their leucoemeraldine and emeraldine states. This and the dependence of the electroactivity on the cathodic limit employed in the experiments, suggest that the loss of electroactivity often reported for pH values above 3–4 is unlikely to be caused by a deprotonation of the emeraldine salt. The effect is more likely due to slow reduction of the fully oxidised PANI (pernigraniline). Experiments with films of different thicknesses indicate that PANI films are not in pH equilibrium with the bulk solution and that the pH within the pores is lowered upon oxidation, probably as a result of the concurrent expulsion of protons from the film. The pH change within the pores is shown to depend on the buffer capacity of the solution.