Rotating disk electrode measurements on the CO tolerance of a high-surfacearea Pt/Vulcan carbon fuel cell catalyst

We examine the electrocatalytic properties of a Pt/Vulcan carbon catalyst t oward the electro-oxidation of CO and CO/H-2 mixtures under proton exchange membrane fuel cell (PEMFC) relevant conditions [60 to 80 degrees C, contin uous reactant flow), employing rotating disk electrode (RDE) measurements. We demonstrate that our recently introduced thin-film RDE technique can he applied to predict the performance of real fuel cell anodes operating on CO -contaminated H-2. The method involves attaching the catalyst particles to a glassy carbon RDE via a thin Nafion film. The thin-film RDE technique ope ns the possibility for the mass-transport-free determination of the electro de kinetics at 100% catalyst utilization. At identical mass-specific curren t densities, the overpotentials for CO/H-2 oxidation measured with the thin -film RDE technique are in excellent agreement with performance data from P EMFC anodes. The kinetics of purl CO oxidation were investigated with CO/N- 2, mixtures, revealing that the CO oxidation activity increases with decrea sing CO partial pressure (negative reaction order). The observed ignition p otential for CO oxidation was the same for both the CO/N-2 and the CO/H-2 m ixtures. Two H-2 oxidation mechanisms in the presence of CO can be distingu ished: (i) a high Tafel slope region at low overpotentials, where H-2 oxida tion occurs in vacancies of the CO adlayer; and iii) a law Tafel slope regi on at high overpotentials where H-2 and CO oxidation occur simultaneously. (C) 1999 The Electrochemical Society. S0013-4651(98)07-057-8. AII rights re served.