Oxygen reduction on a RuxSy(CO)(n) cluster electrocatalyst in 0.5 M H2SO4

A ruthenium-sulfur carbonyl cluster electrocatalyst, RuxSy(CO)(n), was synt hesized by pyrolysis of Ru-3(CO)(12) and elemental sulfur in a sealed ampou le at 300 degrees C. The pyrolyzed compound was characterized by DSC, FT-IR . XRD and SEM (EDX) techniques. The electrocatalytic activity and kinetic p arameters for the molecular oxygen reduction were determined by a rotating ring-disk electrode (RRDE) in a 0.5 M H2SO4 solution at 25 degrees C. The c athodic polarization indicates two Tafel slopes: -0.124 +/- 0.002 V dec(-1) at low and -0.254 +/- 0.003 V dec(-1) at high overpotentials. and first-or der kinetics with respect to O-2 concentration. From the analysis of Levich plots and RRDE results, the oxygen reduction on RuxSy(CO)(n) was determine d to proceed mostly via a multielectron transfer path (4e(-)) to water form ation (> 94%).