127

200°C increased especially at 0.9V. However, as described above, the relative intensity of Pt[Co-Ni]decreased significantly. Therefore, it is considered that fine particles of Pt[Co*Ni] were dissolved predominantly leaving large-sized one (>100 A) undissolved.

Chemical analysis of content for Pt, Co, and Ni in the alloy-electrocatalysts — The Pt, Co and Ni contents in the corroded electrocatalysts were analyzed by ICP(see Fig.4). It is noteworthy that large amounts of both Ni and Co components were dissolved even at the temperature of 200°C and at the potential of 0.7V,i.e., normal operating condition of PAFC except that the atmosphere was Nj. An elevation of temperature form 200°C to 240°C also resulted in a loss of these components. However, the Pt contents of all specimens were approximately constant. Therefore Pt dissolved from alloy could be deposited again as pure Pt particles. The re-deposition of Pt might causc an increase of the crystallite size of Pt as shown in Table 1.

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