The cathodic behavior of the interphase Bi/Bi2O3/electolyte is studied by using electrochemical and optical techniques. Electrochemical evidence indicates the existence of a cathodic process after the bismuth oxide electroreduction, involving the metallic bismuth and the hydrogen produced electrochemically. Impedance data obtained under cathodic polarization indicate that the electrode/solution interphase does not correspond to a simple metal/electrolyte interface. The stability of thin anodic films formed on cathodically pretreated electrodes shows anomalous features, being this behavior dependent on oxide film thickness as well as on transport of species across the film. The results obtained can be reasonably interpreted assuming that during cathodic polarization, the hydrogen absorption into the bismuth substrate takes place. As a result, the cathodic polarization of bismuth could not be a suitable surface pretreatment for electrochemical studies of the bismuth oxide, either they focused on the growth mechanism or the dielectric properties. (c) 2006 Elsevier B.V. All rights reserved.