Rationalisation of time-dependent and voltage-dependent electroactivity in Nafion®/Os(bpy)33+/2+ films in terms of a model that assumes restricted counterion access to non-equivalent redox sites

A model for Nafion(R) loaded with Os(bpy)(3)(3+/2+) is presented, which rationalises measurable properties such as the discrepancy between electroactive amounts measured by cyclic voltammetry and impedance spectroscopy and the inherent peak separation in cyclic voltammetry. The model is based on the concept that some sites are freely accessible to counterions whereas sites which reside in aqueous pools with narrow entrances or sites residing in the more or less hydrophobic phase are accessible only when a sufficient potential gradient is present to overcome a potential barrier. The current is modelled by a Butler-Volmer-like relationship. The influence of counterion size on the electroactive amount is predicted. An observed constant current in small step chronoamperometry gives further support to the model with non-equivalent sites. (C) 1998 Elsevier Science S.A. All rights reserved.