Structure, activity, and stability of the Ru(1-x)Fe(x)Se(y)/C (x = 0.0-0.46, y = 0.4-1.9) catalysts, synthesized via hydrogen annealing of carbonyl precursors, are analyzed using X-ray diffraction, transmission electron microscopy, rotating (ring) disk electrode voltammetry, and cyclic voltammetry. Hydrogen annealing at 400 degrees C enables nucleation of the pyrite phase, which strengthens the catalyst stability for oxygen reduction reaction (ORR) in the acidic electrolyte. Evaluation on the stable Ru(1-x)Fe(x)Se(y)/C catalysts indicates that the ORR activity increases with increasing iron content and Se content. Substitution of base metal Fe enhances the activity and reduces the material cost, but it also increases the H(2)O(2) yield, which is measured less than 3.0% between 0.7 and 0.9 V in contrast to 1.0% of the catalyst without iron. The high activity of Ru(0.54)Se(0.46)Se(1.9)/C decays more rapidly than that of RuSe(2.0)/C in the stability test, probably because Fe and Se are preferentially leached in the potential cycling up to 1.2 V. Still the two catalysts with pyrite structure exhibit much higher durability than the cluster-type catalyst of RuSe(cluster)/C (Ru:Se = 1:0.3) that was not annealed. (C) 2010 Professor T. Nejat Veziroglu. Published by Elsevier Ltd. All rights reserved.