A probe beam deflection study of ion exchange at poly(vinylferrocene) films in aqueous and nonaqueous electrolytes

The ion exchange occurring between a poly(vinylferrocene) (PVF) film and the bathing solution during the oxidation-reduction process was studied by probe beam deflection (PBD) in aqueous and nonaqueous media. In nonaqueous media the results for different electrolyte salts indicate that anions are exchanged. In aqueous media, the ion exchange is strongly affected by the anion present in the solution. In tetrafluoroborate and hexafluorophosphate solutions, cation exchange is observed while in toluenesulfonate solution anion exchange in observed. In perchlorate and trifluoromethanesulfonate solutions a mixed mechanism involving cation and anion exchange is observed. Expulsion of cations precedes anion insertion on oxidation. The ion flux is not affected by the pH (in the range from 1 to 7) or the electrolyte concentration (between 0.1 and 4 M). The kind of ion exchanged appears to correlate with the type of interaction (attractive or repulsive) between redox centers inside the film seen from voltammogram shapes. Ion exchange was also studied during the wetting of the films by electrolyte and shown to be of the same type during the initial cycles of a virgin film in the electrolyte. When a film is left in the reduced state for a period of time, then the next cycle to be recorded reveals a more anodic peak potential and a lower peak current. The ion flux measured by PBD is in the same direction as in continuous cycling.