Membrane electrodes have unique applications. One main possible use is the template synthesis of nanostructures. The proper understanding of the kinetics and mechanisms of synthesis is one of the key goals in this field. However, the usual ideal approximation of membrane electrodes as disk recessed electrodes can be misleading. Based on the studies of diffusion coefficients of o-methoxyaniline interacting with membrane electrodes we report here that the discussed system is much more complicated than originally thought. Our results show that membrane pore geometry changes with the duration of the experiment and it is dependent on the evaporated metal layer, and that these factors influence the value of diffusion coefficients. (C) 2008 Elsevier B.V. All rights reserved.