Electrochemical properties of bilayers of conducting polymers: Polypyrrole with poly(4-styrenesulfonate) ions poly(N-methylpyrrole). Studies of the permeability of the outer layer towards cations

Bilayers of conducting polymers, composed of polypyrrole with poly(4-styrenesulfonate) groups (PPy(PSS)) as the inner film and poly(N-methylpyrroIe) (PMPy) as the outer layer were studied using cyclic voltammetry and the potential step method, measuring both current and charge. The inner layer was a cation exchanging matrix, while the outer one was an anion exchanger. In such a case the current response of the inner film is limited by the cation transport across the outer layer. The permeability of the outer PMPy coating was studied quantitatively by measuring the redox charges of the film in various electrolyte solutions and for different film thicknesses. The permeability of the PMPy layer towards cations was found to rise in the sequence Ba2+, Na+, K+, H+ (low concentration in solution), H+ (higher concentration in solution).