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 applicatio n of a potential step are presented. The procedure for evaluating the excha nge of mobile species (ions and solvent) is illustrated by application of t he combined technique to a poly(o-toluidine) (POT) film redox switching in aqueous HClO4 solutions. A comparison of the predicted PBD profiles calcula ted 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 q uantitatively. The results are consistent with a mechanism where anion exch ange involves a counter flux of solvent, and suggest that a film volume con straint is applicable on the time scale of the experiment. During oxidation and reduction, the EQCM indicates a non-equilibrium movement of anions, co nfirmed by convolution analysis of the associated current and deflection si gnals. (C) 2000 Elsevier Science Ltd. All rights reserved.