Bilayer films, composed of an electronically conducting polymer inner film [polypyrrole/poly(styrenesulfonate) (PP/PSS)] and a redox polymer outer film [poly(vinylferrocene) (PVFc)], were prepared to investigate potential dependent dual ion transport during redox switching. In order to ascertain that the film has an electrochemically distinct bilayer structure, methyl viologen dichloride (MV(2+)Cl(2)) was utilized as an electrochemical probe at reduced PP/PSS. PP/PSS films greater than or equal to 550 nm in thickness gave complete coverage of the metal electrode. At 410 nm thickness coverage was greater than 99% as observed by scanning electron microscopy with small pinholes visible. It was found that the electroactivity and dominant mobile ionic species of the bilayer components (i.e., cation and anion dominant transport properties of PP/PSS and PVFc, respectively) are preserved in the bilayer configuration yielding electrodes with dual ion transport properties. The bilayers have discrete ion transport processes at well separated potentials indicative of independent redox reactions for each component. The amounts of each mobile ionic species was monitored using an electrochemical quartz crystal microbalance (EQCM) and could be controlled by changing the thickness of both inner and/or outer films. The magnitude of the mass changes observed, during oxidation and concurrent cation release from the PP/PSS inner film, scale quantitatively with PP/PSS film thickness, independent of the outer PVFc film thickness. The bilayer possesses a potential window of decreased net mass response in between the redox potentials of PP/PSS and PVFc. Quantification of the mass response during oxidation of the PVFc outer layer was complicated due to high potential contributions of the PP/PSS inner layer. PP/PSS alone exhibits a substantial net mass change between -0.1 V and +0.6 V versus Ag/AgCl, as evidenced by a 1.5 mu g (3.5 g mol(-1)) decrease for a 410 nm thick PP/PSS film cycled in 0.1 M NaClO4(aq), which can be attributed to cation dominant transport. Simultaneous counter-directional solvent flux occurs over this potential window. The net mass change of the bilayer in this potential window is almost negligible in CsClO4 [Delta m congruent to 0.12 mu g (1.2 g mol(-1))] electrolyte and relatively small changes are observed in NaClO4 [Delta m congruent to 0.5 mu g (1.2 g mol(-1))]. These results show that the outer film can act as a barrier to ion, and solvent transport between the inner film and electrolyte, yielding a more balanced counter-directional movement of cations and anions, occurs as the outer film prohibits excessive anion transport to the inner film.