Cells F 3000Stabilization of Platinum Oxygen-Reduction Electrocatalysts Using Gold Clusters. -Pt oxygen-reduction fuel cell electrocatalysts are stabilized against dissolution under potential cycling regimes (a continuing problem in vehicle applications) by modifying Pt nanoparticles with Au clusters. There are insignificant changes in the activity and surface area of Au-modified Pt under the oxidizing conditions of the O2 reduction reaction and potential cycling between 0.6 and 1.2 V in over 30,000 cycles, in contrast to sizable losses with the pure Pt catalyst under the same conditions. In situ XANES and voltammetry data suggest that the Au clusters confer stability by raising the Pt oxidation potential. -(ZHANG, J.; SASAKI, K.; SUTTER, E.; ADZIC, R. R.; Sci.

This report was prepared as an account of work sponsored by an agency of the United States Government. Neither the United States Government nor any agency thereof, nor any of their employees, makes any warranty, express or implied, or assumes any legal liability or responsibility for the accuracy, completeness, or usefulness of any information, apparatus, product, or proctss disclosed, or represents that its use would not infringe privately owned rights. Reference herein to any specific commercial product, process, or service by trade name, trademark, manufacturer, or otherwise dots not necessarily constitute or imply its endorsement, mommendation, or favoring by the United States Government or any agency thereof. The views and opinions of authors expressed herein do not necessarily state or reflect those of the United States Government or any agency thereof. 11 Reaction Pathways and MechanismsReaction pathways, rather than reaction mechanisms, were often analyzed since in many cases, particularly for a four-electron O2 reduction, formulation of the latter proved too complex. These analyses are based on the data obtained by a rotating disk-ring technique which enables the quantitative determination of some of the reaction intermediates. Since the first proposition by Damjanovic et al. (42), there were several reaction schemes proposed for analyzing the diskring data and calculating the rates of various reaction steps (43, 44, 45). The merits of various schemes were considered by Hsueh et al. (46) and Tarasevich et .al. (1). The formulation of the

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