Electrochemical preparation and redox/ion exchange properties of polypyrrole in aqueous sodium hexafluoroaluminate

Abstract

Electrodeposition and redox switching performance of polypyrrole in aqueous solution of sodium hexafluoroaluminate are described. An incorporation of NaAlF62− into the polymer phase is indicated by the EQCM analysis of electrodeposition. A SEM micrograph shows a characteristic morphology of the polymer layer. A mechanism of the redox process of polypyrrole is discussed based on CV and EQCM results involving the measurements performed as a function of a time scale of the redox cycle and a life time of the electrode. Structure determining interactions between polymer sites and counterions are indicated. Participations of ion-pair counterion, co-ion, salt, water, oxygen in the redox process of polypyrrole are discussed. A slow irreversible rearrangement in the structure/composition, inducing a change in the mechanism of the reversible redox process, is postulated to occur during the reduction process of the virgin anion-exchanging polypyrrole. Long time scale processes were observed to result in cation exchange properties accompanied by a substantial decrease in redox activity and/or CV currents of the polypyrrole electrode. The performance of the primary hexafluoroaluminate counterion electrode, prepared in aqueous solution of sodium hexafluoroaluminate, is compared to the secondary hexafluoroaluminate counterion electrode, prepared in a presence of the sodium chloride solution. In general, the CV and EQCM characteristics of the two system are similar due to pronounced contribution of the bathing electrolyte to the performance of the polymer electrode.