ELECTROLYTE EFFECT ON THE DEGRADATION AND DEACTIVATION OF POLYTHIOPHENE THIN-FILMS IN AQUEOUS-SOLUTIONS

Polythiophene (PT) films were deposited on a Pt electrode in acetonitr ile (AN) using BF4-, ClO4-, and CF3SO3- as doping anions and Li+ as th e counter cation, and characterized electrochemically in aqueous solut ions, mainly by cyclic voltammetry. When the same electrolyte as that used for synthesis was used, the current in the redox response decreas ed gradually upon repeating the potential scan. Besides incomplete red uction, oxidative degradation caused by reactions of the cation radica l of the thiophene moieties with H2O and anions as nucleophiles is sup posed to be responsible for the deactivation. When the films were inve stigated in electrolytes different from those used for synthesis, it b ecame evident that the nature of the anion plays a major role in the e lectrochemical behaviour of the polymer. The PT films were also deacti vated in aqueous solutions of TEABF(4), TEAClO(4) and TEACF(3)SO(3) (T EA = tetraethylammonium). The anodic current peak in the redox respons e shifts to more positive potentials; this is caused by the accumulati on of these cations in the film.