Electrolytic Ni + Mo and Ni = Mo + Si coatings were prepared by co-deposition of nickel with silicon and molybdenum powders from a nickel bath in which Mo and Si particles were suspended by stirring. Modification of the surface of the Ni + Mo + Si electrodes was carried out by leaching out of the Si particles in alkaline solution. In this paper coatings modified in that way were denoted as Ni + Mo-Si. Electrochemical measurements were undertaken on both Ni I Mo composite coating and modified Ni + Mo-Si composite coating after thermal treatment in air (700 degrees C, 1 h). It was stated that composite coatings are characterized by very porous surface in comparison with nickel coating after the same thermal treatment. Apparent activity for OER on the obtained coatings was studied by means of both do and ac electrochemical methods in S M KOH. In the Tafel plots determined for the OER, two well defined and the same slopes were observed for all investigated electrodes. This fact indicates that the OER on all obtained electrodes is controlled by the same mechanism. It has been stated that additional ingredients in the coating and modification of the surface cause an increase in electrochemically active surface area and improve electrochemical characteristics of the coatings in OER. (C) 2008 International Association for Hydrogen Energy. Published by Elsevier Ltd. All rights reserved.