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An attempt has been made to measure the absorption cross sections of O2 in the metastable state a1Δg from 1087 to 1700 Å. The absorption is measurable (σa ≥ 3 × 10−19 cm2) from around 1500 Å towards shorter wavelengths. Many band structures overlaying various continua have been seen. Absorption cross sections of O2 in the ground state X3Σg− also have been measured in the same wavelength region and our results agree with previously published values within experimental error. The cross sections of O2(a1Δg) are generally larger than those of O2(X3Σg−) below 1290 Å except at the wavelengths of a few strong bands of O2(X3Σg−).

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 Ptskin (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 ® -coated Pt 2AL -Pt-M/C catalysts in O 2 -saturated 0.1 M HClO 4 solution were evaluated by the use of a multi-channel flow double electrode cell at 65°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 0.6 V and 1.0 V.

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