Polymer Films on Electrodes XI. Electrochemical Behavior of Polymer Electrodes Produced by Incorporation of Tetrathiafulvalenium in a Polyelectrolyte (Nation) Matrix

The electrochemical behavior of the cation exchange polymer Nation containing tetrathiafulvalenium (TTF +) on a platinum sub strate is described. The polymer electrode shows cyclic voltammetric behavior similar to that of solid films of TTF on platinum. In 1.0M KBr the oxidized form of the electroactive molecules in the polymer (TTF § forms nonstoichiometric complexes with Br-. The peak potentials in cyclic voltammetry shift with changes in concentration of supporting electrolyte, temperature, and anion of the supporting electrolyte. Very narrow cyclic voltammetric waves are observed that result in part from attractive interactions between the electroactive molecules. The separation in peak potential of the reduction and oxidation waves is explained by formation of TTFBr07 which stabilizes the oxidized form (TTF § and makes it harder to reduce. Peak potentials for the oxidation and reduction shift closer together as the scan rate is lowered, which is explained by a "square (reaction) scheme." The electrochemistry of layers on electrode surfaces, both solids and polymers, has been investigated by many research groups. The cyclic voltammetric behavior of the surface-confined layers frequently deviates from the theoretical "thin film" behavior of a one-electron nernstian reaction at 25~ i.e., peak width at half-height (hE1/2) of 90.6 mV and no splitting between the anodic and cathodic peaks (2~Ep Epa -Epc ---0) (1). Relatively few films show a hE1/2 significantly smaller than 90.6 mV (2). These narrow cyclic voltammetric (CV) waves were attributed to interactions among the electroactive molecules and phase formation in the layer. Large peak separations observed in cyclic voltammetry at fast scan rates (1 V/sec and larger) have been attributed to slow heterogeneous kinetics and resistance effects in the layer. Even at slow scan rates, where heterogeneous kinetics and resistance usually are not of importance, finite hEp values have been observed. These have been explained by kinetic effects associated with phase for* Electrochem'-cal Society Student M e m b e r . ** Electrochemical Society Act ive Member.