Anion insertion and expulsion in polyaniline electrodes studied by photocurrent transients

The transient current response on a millisecond time scale for polyaniline electrodes subject to a photoflash has been examined in a range of solutions. Differences were seen in the photocurrent profiles determined by the anion present in solution, rather than by the anion of the solution in which the polymer was originally formed. Polyaniline films in HCl and HBF4 displayed both anodic and cathodic photocurrents, with the cathodic photocurrents being more predominant than for films in H2SO4, while films in p-toluenesulfonic, acid showed weaker photocurrents reflecting the lower mobility of the bulky anion. Polyaniline films in HClO4 or acetonitrile showed only cathodic photocurrents at all potentials for polyaniline in the conductive state, the suppression of the anodic photocurrents was related to the strong binding of the perchlorate anion within the positively charged polymer. For thicker films in HCl, the photocurrents in the conducting state remained at a limiting value, while the short-lived photocurrent at 0.3 V declined progressively as the capacitive-type response was dampened. The prolonged photocurrents in the conductive slate are explained in terms of local temperature changes leading to a shift in the state of redox charge. (C) 1998 Elsevier Science Ltd. All rights reserved.