Polythiophene electrogeneration on a rotating disk electrode: The influence of water on polymerization and polymer properties

Abstract

Polythiophene was electrogenerated from acetonitrile solutions using a platinum rotating disk electrode by consecutive potential sweeps, and potential steps. When the rotation rate increases in a 0.1 M thiophene solution, thinner and more passive films were obtained. An increase of the monomeric concentration from 0.1 M to 0.25 M promotes thick polymer layers at high rotation rates again. A competitive electrodic discharge between monomer and water was confirmed for water contents between 0.04% and 1.24% (by weight). The competitive water discharge is responsible for the polymer passivation, as was confirmed by polymer generation at constant potential in different water contents and by voltammetry of active polythiophene electrodes in the background solution with different water contents. At low monomer concentrations the water flow arriving at the electrode increases at increasing rotation rates developing thinner and more passive layers. The strong acidification close to the electrode promoted by the current flow seems to be the origin of a simultaneous chemical polymerization on blocked electrodes. The extensive polymerization at high rotation rates indicates that polymerization takes place through species grafted to the electrode surface. A model of interfacial reactions according with experimental results is proposed.