Redox commuting properties of polyaniline in hydrochloric, sulphuric and perchloric acid solutions

Abstract

In the present work we have studied the pH dependence of the voltammetric response of polyaniline (Pani) in three different electrolytic media: HCl, H2SO4 and HClO4 at constant ionic strength. The electrochemical stability of Pani as a function of the pH is different for the three electrolytes. As the pH increases, the stability limit decreases in the order HCl > HClO4 > H2SO4. The voltammetric data were analyzed based on a theoretical expression for the redox potential as a function of the oxidation degree of the polymer. This analysis allows obtaining the acid dissociation constant for the three electrolytes, and an interaction parameter that reflects the change in the interaction energy between the redox centres of the polymer as the pH is increased. Particularly interesting is the HCl system, in which the pH can be increased up to about 5.0 without loss of the electrochemical activity. A further proof that the current vs. potential response may be represented by a reversible confined redox couple with interactions comes from the pH dependence of the peak current for the three electrolytes. As expected, the acid dissociation constants of the reduced and oxidized polymer do not depend much on the nature of the anions studied here.