ANION INSERTION AND EXPULSION IN POLYANILINE ELECTRODES STUDIED BY PHOTOCURRENT TRANSIENTS

The transient current response on a millisecond time scale for polyani line electrodes subject to a photoflash has been examined in a range o f solutions. Differences were seen in the photocurrent profiles determ ined by the anion present in solution, rather than by the anion of the solution in which the polymer was originally formed. Polyaniline film s in HCl and HBF4 displayed both anodic and cathodic photocurrents, wi th the cathodic photocurrents being more predominant than for films in H2SO4, while films in p-toluenesulfonic, acid showed weaker photocurr ents reflecting the lower mobility of the bulky anion. Polyaniline fil ms 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 per chlorate anion within the positively charged polymer. For thicker film s in HCl, the photocurrents in the conducting state remained at a limi ting value, while the short-lived photocurrent at 0.3 V declined progr essively as the capacitive-type response was dampened. The prolonged p hotocurrents in the conductive slate are explained in terms of local t emperature changes leading to a shift in the state of redox charge. (C ) 1998 Elsevier Science Ltd. All rights reserved.