Voltammetric study of the redox processes of self-doped sulfonated polyaniline

Abstract

Electrochemical redox properties of self-doped copolymer of aniline and m-aminobenzenesulfonic acid (metanilic acid), electrodeposited on platinum electrode, were studied in different electrolytes. Two reversible redox processes with the midpoint potentials of 0.21–0.25, and 0.41 V vs. Ag/AgCl were found for copolymer films of different redox capacity in 0.1 M sulfuric acid solution. Copolymer films are redox active in nearly pH–neutral solutions, however, their activity depend greatly on the cation present in electrolyte. Well expressed redox behavior has been observed in ammonium sulfate, chloride, nitrate, and phosphate buffer pH 7 solutions, whereas suppressed redox properties were found in the corresponding sodium salt solutions. This difference has been discussed in terms of cation exchange between the copolymer film and solution during redox cycling. In an acidic solution, the copolymer shows electrocatalytic behavior for the hydroquinone/benzoquinone redox couple, whereas in neutral solutions no electrocatalysis for this couple, as well as inhibition of redox processes for Fe 3+/2+ and Fe(CN) 6 3−/4− couples was observed.