Pd0.5NixSe(0.5-x) electrocatalysts with different chemical composition, X = 0.25, 0.35, 0.45, were synthesized by a NaBH4 reduction of PdCl2, NiCl2 and SeO in a THF solution and evaluated for the oxygen reduction reaction (ORR) in acid media by electrochemical techniques of rotating disk electrode (RDE) and rotating ring-disk electrode (RRDE). The electrocatalysts were characterized by scanning electron microscopy (SEM), X-ray diffraction (XRD) and CO adsorption/stripping. The relation of Se to Ni in the samples has a profound effect on the nature of the cathode catalytic activity toward the oxygen reduction process, enhanced as the Se content in the electrocatalysts was reduced. Electrochemical results show that the ORR takes place by a multi-electron charge transfer process (n = 4e(-)) with the formation of less than 1% of hydrogen peroxide. The enhanced activity was attributed to the high active surface area deduced from CO adsorption/stripping analysis. The research activities are reported within the focus on the activity-stability of the bimetallic chalcogenides electrocatalysts. (C) 2010 Professor T. Nejat Veziroglu. Published by Elsevier Ltd. All rights reserved.