Thermodynamic changes in ion and solvent populations accompanying redox switching in polyvinylferrocene films

The electrochemical quartz crystal microbalance (EQCM) was used to study redox induced changes in equilibrium ion and solvent populations of polyvinylferrocene (PVF) films. The effects of solution concentration and the identities of the cation (co-ion) and anion (counter ion) were investigated in aqueous sodium and perchlorate salt solutions. The redox behaviour of these PVF films is dependent on the bathing electrolyte composition. At low concentrations, the film is permselective: only counter ions (and solvent) participate during film oxidation. At higher concentrations, permselectivity fails, and oxidation is accompanied by the ingress of salt (both co- and counter ions). Potentiometric data agree with this model. Regardless of the concentration and the electrolyte studied, some solvent transfer occurs as a consequence of solvent activity coefficient changes that accompany redox switching.