Oxidation kinetics of polypyrrole films: Solvent influence

During electrochemical reactions films of conducting polymers exchange counterions, for charge balance, and solvent, for osmotic balance, with the electrolyte. A physical process drives the solvent exchange: the solvent cannot be considered as a reactant. Here we explore the solvent influence on the reaction rate. The oxidation empirical kinetics of polypyrrole film was attained from the chronoamperometric responses to potential steps in solutions of different solvents and the same electrolyte. Seven different organic solvents were studied: two protic (water and methanol) and four aprotic (acetonitrile, acetone, N,N-dimethylformamide dimethylsulfoxide and benzonitrile) solvents. The attained reaction coefficients in a solvent decrease exponentially for deeper reduced initial states and, under similar initial reduced conditions, change among the different solvents for one order of magnitude. A good correlation is attained between empirical and theoretical results when the kinetic coefficient is related to the dipolar moment and dielectric constant of each solvent. The solvent, even if it cannot be considered as a reactant, has a strong influence on the reaction rate of electrochemical reactions involving dense reactive gels of conducting polymers. (C) 2016 Published by Elsevier B.V.