Electrocatalytic activity of Pt alloys with Ni, Co, and Fe, formed by sputtering, was investigated with regard to the oxygen reduction reaction (ORR) in perchloric acid solution. Hydrodynamic voltammograms with rotated electrodes were used to measure the electrocatalytic activity. Maximum activity was observed at ca. 30, 40, and 50% content of Ni, Co, and Fe, respectively, by which 10, 15, and 20 times larger kinetic current densities than that of pure Pt were attained. X‐ray photoelectron spectroscopy analysis of the surfaces after the reaction indicated that the active surfaces were covered by a few monolayers of Pt. We present an enhancing mechanism for the ORR based on an increased d‐electron vacancy of the thin Pt surface layer caused by underlying alloy. Results of this work contribute in development of new active cathode catalysts for fuel cells used as power sources of electric vehicles, etc. © 1999 The Electrochemical Society. All rights reserved.

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Electrocatalytic activity of PtNi alloy surfaces formed by sputtering was investigated toward oxygen reduction reaction (ORB) in perchloric acid solution. Hydrodynamic voltammograms with rotated electrodes were utilized to measure the activity. Maximum activity was observed at ca. 30% of Ni content by which a ten times larger kinetic current density than that of pure Pt was attained. X-ray photoelectron spectroscopy analysis of the surfaces after the reaction indicated that the active surfaces were completely covered by Pt. The effect of Pt interatomic distance at the surface or of surface roughening was excluded as the cause of high activity. We present a mechanism of the ORR based on d electron vacancy at the surface Pt due to Ni content a few monolayers below the surface. This type of catalyst will contribute in development of fuel cells for electric vehicles and other applications.

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The high-power performance of proton exchange membrane fuel cells (PEMFC) decreases as the Pt loading or Pt surface area decreases due to oxygen transport constraints. This has limited the Pt reduction of a fuel cell below the current ∼0.2 mg Pt /cm 2 MEA . In this paper, the performance of a Ptmonolayer core−shell catalyst (Pt ML /Pd/C) was studied with a particular focus on high-current-density operation. Although conventional Pt/C electrodes with low Pt loading showed a substantial voltage falloff at high current densities, Pt ML /Pd/C showed superior performance due to its greater Pt surface area. We show that Pt loading can be reduced to a level as low as 0.025 mg Pt /cm 2 without noticeable transport-related losses. This suggests considerable potential for further fuel cell cost reduction. The performance and microscopic properties of the catalyst were also studied after accelerated stability tests. The degradation mechanism and pathways for future development are also discussed.

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