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

We examine the electrocatalytic properties of a Pt/Vulcan carbon catalyst toward the electro-oxidation of CO and CO/H sub 2 mixtures under proton exchange membrane fuel cell (PEMFC) relevant conditions (60 to 80 deg C, continuous reactant flow), employing rotating disk electrode (RDE) measurements. We demonstrate that our recently introduced thin-film RDE technique can be applied to predict the performance of real fuel cell anodes operating on CO- contaminated H sub 2 . The method involves attaching the catalyst particles to a glassy carbon RDE via a thin Nafion film. The thin-film RDE technique opens the possibility for the mass-transport-free determination of the electrode kinetics at 100% catalyst utilization. At identical mass-specific current densities, the overpotentials for CO/H sub 2 oxidation measured with the thin-film RDE technique are in excellent agreement with performance data from PEMFC anodes. The kinetics of pure CO oxidation were investigated with CO/N sub 2 mixtures, revealing that the CO oxidation activity increases with decreasing CO partial pressure (negative reaction order). The observed ignition potential for CO oxidation was the same for both the CO/N sub 2 and the CO/H sub 2 mixtures. Two H sub 2 oxidation mechanisms in the presence of CO can be distinguished: (i) a high Tafel slope region at low overpotentials, where H sub 2 oxidation occurs in vacancies of the CO adlayer; and (ii) a low Tafel slope region at high overpotentials where H sub 2 and CO oxidation occur simultaneously.