The synthesis, characterization and optimization of RuxSey catalyst loading as a cathode electrode for a single polymer electrolyte membrane fuel cell, PEMFC were investigated. RuxSey catalyst was synthesized via a decarbonylation of Ru-3(CO)(12) and elemental selenium in 1,6-hexanediol under refluxing conditions for 2 h. The powder electrocatalyst was characterized by scanning electron microscopy (SEM), atomic force microscopy (AFM), and examined for the oxygen reduction reaction (ORR) in 0.5M H2SO4 by rotating disk electrode (RDE) and in membrane-electrode assemblies, MEAs for a single PEMFC. Results indicate the formation of agglomerates of crystalline particles with nanometric size embedded in an amorphous phase. The catalyst exhibited high current density and lower overpotential for the ORR compared to that of Ru-x cluster catalyst. Dispersed RuxSey catalyst loading on Vulcan carbon was optimized as a cathode electrode by performance testing in a single H-2-O-2 fuel cell. (C) 2010 Professor T. Nejat Veziroglu. Published by Elsevier Ltd. All rights reserved.