Charging Processes in Electroactive C60/Pd Films: Effect of Solvent and Supporting Electrolyte

Abstract

The electrochemical properties of solid films deposited on an electrode surface by simultaneous electrochemical reduction of C60 and palladium(II) acetate trimer in an acetonitrile/toluene mixture have been studied using cyclic voltammetry. The electrochemical switching between the doped (conducting) and undoped (nonconducting) states involves both electron and ion transport within the film. The overall control of charge percolation through the C60/Pd electroactive material is governed by the transport of cations. The ion transport depends both on the nature of solvent and supporting electrolyte. The size of solvent molecule is the major factor determining the degree of solvent swelling of the layer. In the case of small solvent molecules, the C60/Pd film exhibits a reversible redox behavior. For larger molecule solvents, the voltammograms show a departure from reversibility. The reduction of the layer is accompanied by changes in its morphology allowing for the solvent swelling of the film also in the case of large molecule solvents. The electrochemical response of the layer is not affected by the anions of the supporting electrolyte. However, a strong influence of both nature and concentration of supporting electrolyte cations on the redox properties of the layer is observed, since these cations are incorporated into the C60/Pd layer. The redox ability in solutions containing large cations is considerably reduced. The activation of the film at negative potentials results in an increase of the doping level. The stability of the films is affected by the potential range over which they are examined. Scanning to highly negative potentials results in the loss of redox activity due to removal of the film from the electrode surface.