Electrochromism of Polyaniline Film Prepared by Electrochemical Polymerization

: Polyaniline films were prepared by galvanostatic oxidation of aniline in 0.1 M H₂SO₄aqueous solution, and their electrochromic properties were investigated by cyclic voltammetry, spectroelectrochemical measurements, and ESR spectroscopy. Polyaniline films showed multiple color changes (transparent yellow-green-blue) depending on the electrochemical reactions in the potential range -0.2 to 0.8 V vs. SCE. The cyclic voltammogram of a polyaniline film in 0.1 M H₂SO₄aqueous solution showed two anodic peaks at 0.2 and 0.7 V, together with large capacitive background currents. The color of polyaniline films changed from transparent yellow to green at the anodic peak around 0.2 V and gradually changed from green to dark blue at potentials higher than 0.3 V. The color change from transparent yellow to green is due to the formation of Wurster-type radical cations at 0.2 V, and that from green to blue is due to the formation of a diimine structure and doped states with SO₄^2-in the polymer at potentials above 0.3 V. The deterioration of electrochromic properties is caused by hydrolysis of the diimine structure formed by oxidation at 0.7 V.