Oxygen Reduction Reaction Activity of Carbon-Supported Pt-Fe, Pt-Co, and Pt-Ni Alloys with Stabilized Pt-Skin Layers

We have prepared carbon-supported Pt-M (M = Fe, Co, and Ni) alloy nanoparticles with uniform size and composition as cathode catalysts for polymer electrolyte fuel cells. In order to protect the underlying Pt-M alloy from dealloying and maintain high mass activity for the oxygen reduction reaction (ORR), two atomic layers of Pt-skin (Pt-2AL) were formed on the Pt-M nanopartcicles. By means of various types of analysis, including X-ray diffraction (XRD), inductively coupled plasma mass analysis (ICP-MS), thermogravimetry (TG), and transmission electron microscopy (TEM), the formation of monodisperse Pt-2AL-Pt-M/C was confirmed. The kinetically-controlled ORR activities (mass activity, MA(k), and area-specific activity, j(k)) for the ORR at Nafion (R)-coated Pt-2AL-Pt-M/C catalysts in O-2-saturated 0.1 M HClO4 solution were evaluated by the use of a multi-channel flow double electrode cell at 65 degrees C. It was found that the initial value of MA(k) at Pt-2AL-PtNi/C was the highest, i.e., 3.3 times higher than that at a commercial catalyst, carbon-supported Pt (c-Pt/C). In contrast, the Pt-2AL-PtCo/C catalyst exhibited superior durability, so that dealloying was almost entirely suppressed, together with a great mitigation of the particle agglomeration after applying 10(4) cycles of potential steps between 0.6V and 1.0 V. (C) The Electrochemical Society of Japan, All rights reserved.