The composition of the passive layers formed on Zn electrode in naturally aerated and de-aerated 0.1 M KClO4 Solution were studied using X-ray photoelectron spectroscopic measurements (XPS). A correlation between the presence of dissolved 02 and the formation of an interior passive layer was carried out. Librated Cl- from the perchlorate reduction reaction was detected in its solutions during Zn electrode polarization. The librated Cl- concentration reached its maximum value at -1.4 V. Moreover, in the studied potential range the perchlorate reduction rate increases in absence of dissolved oxygen. Chrono-amperometry and electrochemical impedance spectroscopy (EIS) were performed for the stationary and the rotating disc Zn electrodes in naturally aerated and de-aerated 0.1 M KClO4 solution. EIS technique showed a change in the electrode impedance with the experimental conditions as a result of changing the reactions occurring in the electrode vicinity. The obtained data were fitted to three different equivalent circuits depending on the electrode potential. The protective nature of the passive layers formed in different experimental conditions was found to decrease with rotating the electrode and de-aerating the solution. (c) 2007 Elsevier Ltd. All rights reserved.