Electrical models for metal electrodes that are shielded from the electrolyte by a partially insulating layer are discussed. It is shown that the structure of the electrical model depends on the degree of adhesion between the solid phases involved. The results are then extended to systems in which two layers showing different properties coexist on the electrode surface. Wherever relevant, reference is made to experimental results and to systems that have been described in the literature. © 2000 Akadémiai Kiadó.