The electrochemical reduction of perchlorate anion has been studied in a cell with a nickel working electrode and a platinum counter electrode in concentrated solutions of HClO4. Significant reduction of perchlorate to chloride ions occurs on the nickel cathode in the potential region where hydrogen evolution occurs. It is shown that the mechanism of this process involves platinum deposited in small amounts on the cathode as a result of oxidation of the platinum anode in the perchloric acid solution. The reduction of perchlorate is accompanied by oxidation of the nickel cathode, which is attributed to chlorate ions formed in the initial step of perchlorate reduction. Changes in the surface structure of the nickel electrode have been followed using atomic force microscopy. (c) 2005 Elsevier Ltd. All rights reserved.