Kinetic study of oxygen electro-reduction on RuxSy(CO)(n) based catalyst in 0.5 M H2SO4

The kinetics of molecular oxygen reduction was examined on a novel Rutheniu m-sulfur carbonyl cluster electrocatalyst, synthesized by pyrolysis at 300 degreesC. The experiments were performed by steady stale measurements in a rotating-ring-disc-electrode(RRDE) in 0.5 M H2SO4 at 25 degreesC. For this study the electrocatalyst was supported on carbon paste. It was found that a maximum of 5.5% of hydrogen peroxide is formed at c.a. 0.3 V vs. NHE. Thi s means that O-2 is mainly reduced to water by a four electron pathway. At least three zones of different mechanism could be detected for the O-2 redu ction on Ru(x)Sy(CO)(n). In a first zone (0.67-0.35 V) all the three princi pal reactions of the Damjanovic's model [1] with k(3) greater than or equal to k(2) occur. In the 0.33-0.20 V zone an H2O2 accumulation is observed, k (2) > k(3), and the reaction intermediate is well detected in the ring elec trode. In the more cathodic region (0.31-0.03V) a new zone of occurrence of the three main reactions appears and the small peroxide quantities are slo wly reduced to water In all the three zones k(1) > k(2)..