Chronoamperometric resolution of ion and solvent transfers at a poly(o-toluidine) modified electrode by combined electrochemical quartz crystal microbalance (EQCM) and probe beam deflection (PBD)

Combined electrochemical quartz crystal microbalance (EQCM) and probe beam deflection (PBD) measurements on short time scales following the application of a potential step are presented. The procedure for evaluating the exchange of mobile species (ions and solvent) is illustrated by application of the combined technique to a poly(o-toluidine) (POT) film redox switching in aqueous HClO4 solutions. A comparison of the predicted PBD profiles calculated from the current and mass responses to that of the measured PBD signal, by temporal convolution analysis, enabled the contributions of anion (ClO4-) and solvent (H2O) transfer at the first redox step to be discriminated quantitatively. The results are consistent with a mechanism where anion exchange involves a counter flux of solvent, and suggest that a film volume constraint is applicable on the time scale of the experiment. During oxidation and reduction, the EQCM indicates a non-equilibrium movement of anions, confirmed by convolution analysis of the associated current and deflection signals. (C) 2000 Elsevier Science Ltd. All rights reserved.