An electrochemical impedance characterization of hydride electrodes at different states of discharge (SOD) is presented. A physicochemical model is developed in order to simulate impedance data. The impedance function derived from the model takes into account the porous nature of the electrode material considering a finite conductivity for both the solid and liquid phases. The hydrogen absorption/desorption processes, taking place at the walls of spherical alloy particles of average size, are described in terms of a kinetic scheme for hydrogen adsorption coupled to hydrogen diffusion into the electrode material. The state of discharge of the electrode is related to the boundary conditions necessary to solve the transport equations. (C) 2004 Elsevier Ltd. All rights reserved.