Influence of the electrolyte cation and anion sizes on the redox process of PPy/PVS films in acetonitrile solution

Polypyrrole/poly(vinyl sulfonate) (PPy/PVS) films have been synthesized by a potentiodynamic method in aqueous solution. The voltammetric study of this polymer in acetonitrile (MeCN) reveals an anomalous behavior of its redox process in the three electrolytes used: LiClO4, LiF3CSO3, and (Bu)(4)NClO4. The anion and cation sizes of the electrolyte clearly affect the reduction/oxidation process of a PPy/PVS film in MeCN medium. This result is explained by both anions and cations participating during the redox reaction of this polymer in MeCN medium: initially, the cations penetrate the polymer forming ion pairs with sulfonate groups, and the anions behave as the main mobile species during the potential sweeps. However, a large cation or anion will penetrate with difficulty inside the polymer, providing a lower amount of electroactive polymeric chains and a lower value of peak charges.