Quartz crystal microbalance and probe beam deflection studies of poly(1-hydroxyphenazine) modified electrodes

Abstract

Quartz crystal microbalance (QCM) and probe beam deflection (PBD) were used to evaluate the exchange of mobile species (ions and solvent) during the redox reaction in poly(1-hydroxyphenazine) in aqueous acidic media. Both techniques indicate clearly two separate ion exchange steps with successive uptake and expulsion of ions and solvent molecules. The PBD and QCM results are consistent with a redox mechanism where protons are inserted in the first reduction step and anions are expelled in the second reduction step. During oxidation the process is inverted. At fast scan rates or potential jump experiments, however, QCM indicates a transient insertion of excess anions in the first oxidation step with a corresponding successive ion pair expulsion. Anion exchange at the more negative potentials involves a counter flux of solvent. Mass balance shows that the water content of the film is higher in its reduced state. The different processes are rationalized on the basis of electron/ion transfer coupled with protonation/deprotonation reactions and a potential pH diagram for the stability domains of the various states of the polymer is suggested.