This paper deals with the electrochemical characterisation of Ni/Al-Cl hydrotalcite modified electrodes. The electrochemical impedance spectroscopy technique has been used in order to study the electronic and ionic conduction, both inside and on the surface of the material. The electronic and ionic contributions have been separated and the behaviour of the respective parameters has been studied as a function of the potential. In order to determine the kinetic limiting step of the overall electrochemical process we performed experiments at different temperatures, and calculated the activation energies of the electron hopping process and ion transport process. In addition we studied the behaviour of the system at different OH- concentrations (pH 9.7-12.8) with the aim of clarifying the role of OH- ions in the electrochemical process. (C) 2003 Elsevier Science Ltd. All rights reserved.