Oxygen reduction on a high-surface area Pt/Vulcan carbon catalyst: a thin-film rotating ring-disk electrode study

We describe the adaptation of the recently developed thin-film rotating dis k electrode method and its application in a rotating ring disk configuratio n (RRDE) to the investigation of the oxygen reduction reaction (orr) on a s upported catalyst powder (PtVulcan XC 72 carbon). This allows the determina tion of kinetic data, such as reaction orders or apparent activation energi es, for the orr directly without mathematical modeling. Collection experime nts reveal a potential and rotation rate independent collection efficiency. RRDE measurements allow. for the first time, the direct determination of t he fraction of peroxide production juring oxygen reduction on supported cat alysts. Finally, comparison of measurements in 0.5 M H2SO4 and 0.5 M HClO4, respectively, reveals a significant effect of (bi)sulfate adsorption on th e orr activity. On the basis of the present results, predictions are made o n the kinetic limit of the orr in polymer electrolyte fuel tells, in the ab sence of ohmic and mass transport resistances at 100% utilization. (C) 2001 Elsevier Science B.V. All rights reserved.