The dynamical behavior of the electrochemical polymerization of indole on Fe in acetonitrile–water mixtures

This study reports on the stability of polyindole (PInd) films on Fe. Current oscillations emerge during the potentiostatic polymerization of indole upon its anodic oxidation on an Fe electrode in acetonitrile containing tetrabutyl-ammonium tetrafluoro-borate (N(Bu)4BF4). The oscillatory response of the system depends on the concentration of water, indole (Ind) and N(Bu)4BF4. For low concentrations of N(Bu)4BF4, the polymerization of Ind is possible and is enhanced in the presence of H2O. The addition of H2O leads also to an increase of the Fe dissolution. Increasing the concentration of Fe3+ ions at the Fe|polymer interface induces a mechanical instability of the polymer film. The origin of the present dynamical behavior is discussed on the basis of a breakdown and reconstruction of the polyindole film due to the accumulation of Fe3+ ions at the Fe|polymer interface. The kinetics of the indole polymerization coupled with the Fe electrodissolution includes the catalytic oxidation of indole by Fe3+ ions.