Rechargeable batteries based on poly(aniline-co-o-aminophenol) and the protonation of the copolymer

The battery consists of a zinc electrode, a poly(aniline-co-o-aminophenol) (copolymer) electrode and a solution consisting of 2.5 M ZnCl2 and 3.0 M NH4Cl. In the region pH 4.40-4.70, an anodic peak and a cathodic peak appear on the cyclic voltammograms of polyaniline, however; two anodic peaks and two cathodic peaks appear on the cyclic voltammograms of the copolymer at the scan rate of 60 mV s(-1). The energy density of the battery is slightly affected by pH value in the pH range 4.40-5.00 in this solution. The capacity density and the energy density of the copolymer at pH 4.70 are 103.0 A h kg(-1) and 120.4 W h kg(-1), respectively, at a constant current discharge of 0.5 mA cm(-2), which are 31.2 and 39.8% higher than those of polyaniline at pH 4.40 and under the discharge of 0.25 mA cm(-2), respectively. The reduced copolymer can not be oxidized spontaneously in the above solution of pH 5.00, but can be oxidized spontaneously in air and 0.2 M H2SO4 solution. The oxidation extent of the reduced copolymer is about 60% in 0.2 M H2SO4 solution at a given time. The spontaneous oxidation of the reduced copolymer is caused by oxygen, whereas the acid plays an important role in the catalytic action on the oxidation of the reduced copolymer. The reduced copolymer can be protonated in 0.2 M H2SO4 solution, based on its color change. (C) 2004 Elsevier B.V. All rights reserved.