Electrode reactions of several dissolved hydroquinones on a polyaniline-modified electrode and what occurs in the polyaniline

A conductive polymer polyaniline (PANI) was easily prepared on the electrode surface as a stable film by the electropolymerization of aniline in an acidic solution. In McIlvaineʹs buffer solution whose pH exceeded 4, no redox current of the dissolved species was observed on the PANI-modified electrode because PANI acted as an electric insulator. Even in a less acidic solution, the redox current of the dissolved hydroquinone was evident. On the other hand, in the potential region greater than 0.7 V vs. Ag/AgCl, PANI acted as an electric insulator. Even in the electroinactive potential region, the redox current of the dissolved p-dimethoxybenzene was evident. These two electrochemical responses of the PANI film-modified electrode are caused by processes in which hydroquinone and p-dimethoxybenzene selectively permeate through the PANI film to reach the electrode substrate. The analyses of the rotating disk electrode (RDE) voltammograms using a PANI-modified RDE and steady-state current-potential curves using a PANI pellet electrode revealed that hydroquinone and p-dimethoxybenzene were concentrated in the PANI during the electro-oxidation. Furthermore, the concentration of hydroquinone and p-dimethoxybenzene increased the electric conductivity of the PANI from 6.50 × 10− 7 to 2.73 × 10− 3 S/cm for hydroquinone and from 0.64 to 1.92 S/cm for p-dimethoxybenzene.