Electrochemical characterization in nonaqueous electrolyte of polyaniline electrochemically prepared from aqueous media

Polyaniline film electrodes were characterized in nonaqueous electrolyte following their electrochemical preparation in aqueous media. More specifically, polyaniline films were deposited galvanostatically at the surface of platinum or gold electrodes by anodic electrochemical polymerization from a 0.5 M aniline-1 M HCl aqueous solution. The polyaniline film electrode was then dried and its electrochemical behavior was evaluated in nonaqueous electrolyte (LiClO4-acetonitrile). Stable cyclic voltammograms were recorded between -0.1 and 1 V in the nonaqueous media, which represents a much wider range than in aqueous acidic media. In the latter case the positive potential limit must be restricted to about 0.7 V in order to avoid oxidative degradation of the polymer. Electrochemical impedance spectroscopy was used to determine the charge capacity of the polyaniline film electrode as a function of film thickness and electrode potential. A linear relationship was observed between the low-frequency capacitance of the polyaniline electrode and the amount of deposited polymer (e.g., charge used to grow the polymer). This indicates that even for the thickest film (deposited charge of 10 C/cm(2)) most of the polyaniline is electrochemically accessible at the low frequency of 5 mHz. The thinnest polyaniline film electrode (deposited charge of 0.2 C/cm(2)) was also characterized by the electrochemical quartz crystal microbalance technique and it was found that ionic transport is dominated by the movement of anions.