ELECTROOXIDATION OF ANILINE AND ELECTROCHEMICAL-BEHAVIOR OF THE PRODUCED POLYANILINE FILM ON CARBON-FIBER ELECTRODES IN AQUEOUS METHANOLIC SOLUTIONS

The anodic oxidation of aniline is investigated on PAN-based carbon fibre electrodes, in aqueous methanolic solutions of various pH values. The anodic peak of aniline is diffusion controlled and its height depends absolutely linearly on the concentration of the solution. This is of importance for the determination of aniline in aqueous methanolic solutions. The cyclic voltammetric data showed that the electro-oxidation product of aniline is ''polyaniline'' with a structure containing p-quinonediimine units which exhibit a couple of well-defined redox peaks with heights proportional to the potential sweep rate, indicating the existence of species attached to the electrode surface. Impedance measurements have additionally been used to characterize the electrical properties of the polyaniline-film on the carbon fibres under different conditions. In the potential range of -0.2 to 0.8 V vs. sce, the polyaniline coated carbon fibre electrodes are very stable and exhibit relatively high electronic conductivity and charge capacitance. After remaining on the electrodes at potentials more positive than 0.8 V, the polyaniline film undergoes an oxidative degradation which leads to a decrease of the charge capacitance. A loss of the film conductivity is observed at potentials more negative than -0.2 V vs. sce and is attributed to the fact that the polyaniline film exists in its reduced state.