In this study, Co-based selenides with various selenium contents have been synthesized by heating dodecacarbonyltetracobalt [Co-4(CO)(12)] and elemental selenium in 1,6-hexanediol solvent under refluxing conditions. The synthesized catalyst powders are characterized by X-ray diffraction (XRD) and scanning electron microscopy (SEM). The samples exhibit cauliflower-like surface morphologies and reveal the crystalline characteristics of orthorhombic CoSe2 compound. Electrocatalytic performances of the Co-Se compounds for the oxygen reduction reaction in 0.5 M H2SO4 electrolyte are evaluated by rotating disk electrode (ROE). Co-Se catalysts are electrochemical stable in the potential range of 0.05-0.80 V (vs. NHE). The catalytic activity changes with increasing selenium content, and the highest activity is obtained at 67.1 mol% Se in the catalyst, which can be attributed to the modification of selenium element on the electronic structure of cobalt. (C) 2012 Elsevier B.V. All rights reserved.