Redox history effects accompanying the electrochemical cycling of poly(vinylferrocene)

Cyclic voltammetric studies of poly(vinylferrocene), PVF, in aqueous sodium perchlorate, sodium p-toluenesulfonate, and sodium naphthalenesulfonate solutions revealed unexpected history effects. The films contain redox sites in two local environments. One type of ferrocene site is in a compact, unsolvated environment; it undergoes redox switching in NaClO₄ with only the transfer of counter ions. The other type of ferrocene site is in a more diffuse environment; it undergoes redox switching with the transfer of perchlorate counter ion and water. Only the latter sites can accommodate large anions (toluenesulfonate or naphthalenesulfonate), and therefore undergo redox switching in such media. Upon multiple redox cycling, these large anions get progressively locked into the structure, thereby blocking the diffuse sites. Upon transfer back to NaClO₄ solution, only the "compact" sites are able to undergo redox switching.