Stability of electrochemically prepared polyaniline films in aqueous and organic solutions.

Electroactive polyaniline films have been grown by galvanostatic, potentiostatic and cyclic voltammetry techniques in organic solutions based on LiClO4 or anilinium tetrafluoborate as salts and acetonitrile or acetonitrile/nitromethane mixtures as solvents. After storage of these films in a 1 M H2SO4, Na2SO4 aqueous solution, their stability was tested by cyclic voltammetry and impedance spectroscopy in this solution. Different levels of retention of the anodic charge have been found depending on the electrochemical technique and preparation solution. The impedance tests have revealed limited changes in the charge transfer resistance upon storage. This has been interpreted on the basis of a limited deactivation of the films, which in some cases would instead experience physical changes. Confirmation of this assumption was obtained via an SEM experiment. Films prepared by cyclic voltammetry in the above acidic solution and stored in acetonitrile-or propylene-carbonate-based electrolytes show major degradation processes, as evidenced by the appearance of quinone-like compounds and the marked increase in the charge transfer resistance. Finally, films prepared by different electrochemical techniques in acetonitrile-based solutions and stored in LiClO4-acetonitrile reveal moderate degradation phenomena.