Carbon-supported and non-supported cluster-like RuxSey were synthesized in aqueous media. The structure and morphology were analyzed by XRD and TEM, respectively. Particles dispersed uniformly on the support with an averaged size of 2.1 nm were obtained. The oxygen reduction reaction (ORR) in presence of HCOOH was investigated by means of rotating disk electrode at 25 degrees C on RuxSey nanoclusters. The kinetics of HCOOH oxidation for non-supported and carbon-supported RuxSey catalysts was analyzed. A reaction order of 1/1.4 and 1/1.6 was determined for RuxSey and RuxSey/C, respectively. This reaction order indicates that the reaction mechanism is similar to Pt/C. The chalcogenide catalyst showed a high tolerance and selectivity towards the ORR in electrolytes containing up to 0.1 M HCOOH. At the highest formic acid concentration (5 M) the potential, at e.g. current density of 0.2 mA cm(-2), shifts to negative for non-supported and carbon-supported RuxSey by 0.24 V and 0.28 V. respectively. The results reported in this work are the basis for overcoming the negative impact of fuel cross-over in microfluidic formic acid fuel cells that currently use Pt as cathode catalyst. (C) 2010 Elsevier B.V. All rights reserved.