Electrochemical reactions concerned with electrochromism of polyaniline film-coated electrodes

Abstract Mechanisms of the electrochromic reactions of polyaniline film-coated electrodes were investigated in acid solutions in the potential range between −0.2 V and 0.6 V vs. SCE, where the color of the film changes from transparent yellow to green, depending on the potential. It was suggested from spectro-electrochemical measurements and rotating ring-disk electrode studies that two kinds of redox reactions were involved in the electrochromic reaction of polyaniline. One of these is concerned with proton addition/elimination reactions which give a couple of well-defined voltammetric waves at potentials less positive than 0.3 V vs. SCE, and relates to the color change from yellow to yellowish green or vice versa. The other reaction, which occurs mainly at potentials more positive than 0.3 V, does not give any appreciable voltammetric waves, but gives solely, large capacitive currents, and relates to the color change from yellowish green to green or vice versa. The large capacitive currents cause insertion of the electrolyte anions into the polyaniline film in the course of its oxidation and elimination of the inserted anions during its reduction.