Multi-technique study of the anodic degradation of polyaniline films

Polyaniline (PANI) films, formed by potential cycling methods on Au electro des in sulfuric acid solutions, were anodically degraded with time at ca. 1 V versus RHE. Ellipsometric and cyclic voltammetric data suggest that colo red species are formed within the film, perhaps containing quinone endgroup s, and the bulk of the film dissolves uniformly creating greater porosity. This model of film degradation has been supported by transmission electron microscopy (TEM) studies of cross-sectional samples of PANI films. Both TEM and ellipsometry also showed that the PANI film is not delaminated, and is very resistant to anodic dissolution/degradation. Concurrent in situ mass measurements suggest that, in the early stages of film degradation, some re gions of the film become electrochemically inactive, although the nature of the charge compensation mechanism of the PANI redox reaction remains unalt ered. When no further him degradation can be accomplished, the mass data sh ow that a substantial quantity of largely inactive film material is still p resent on the electrode surface. Furthermore, the change in the redox poten tial and the invariant charge compensation stoichiometry suggests that, alt hough the final degraded him is a different material from the newly formed PANI film, only those portions of the him that have PANI characteristics ar e electrochemically active. (C) 1998 Elsevier Science S.A. All rights reser ved.