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.