The present paper presents a study of the RuxCrySez chalcogenide electrocatalyst based on physical-chemical characterization through scanning electron (SEM), atomic force (AFM) microscopy and energy dispersion elemental analysis (EDS), thermal stability using differential scanning calorimeter (DSC), electrochemical kinetics towards the oxygen reduction reaction (ORR) in acid media by rotating ring-disk electrode (RRDE) and single and three-stack membrane-electrode assembly (MEA) performance as a function of catalyst loading (10%, 20% and 40% W from 0.2 to 2 mg cm(-2)). Results indicate an electrocatalyst with chemical composition of Ru6Cr4Se5. AFM images showed 80-160 nm nanoparticle agglomerates. Good thermal stability of the cathode Ru6Cr4Se5 was established after 100 h of continuous operation. The electrochemical kinetics study (RRDE) resulted in a electrocatalyst with high activity towards the ORR, preferentially proceeding via 4e(-) charge transfer pathway towards water formation (i.e., O-2+4H(+)+4e(-)-> 2H(2)O), With a maximum of 2.8% H2O2 formation at 25 degrees C. Finally, MEA tests revealed a maximum power density of 220 mW cm(-2) with a catalyst loading of 20 wt% at 1.6 mg cm(-2). (C) 2007 Elsevier B.V. All rights reserved.