20

*after holding at 120°C/air for 14hours in h3po4 (ca. 100%)

*after holding at 120°C/air for 14hours in h3po4 (ca. 100%)

The specific surface area of the catalyst was decreased significantly by the treatment with a relatively mild condition of200°C at 0.7 V. At higher temperature or higher potential condition, that is severer condition, surface area became lower value. XRD of the catalysts under such a condition indicated that large-sized (ca. 100A) Pt particles were formed accompanied by a dessolution of fine Pt[Co' Ni] alloy particles (see abstract by Nakajima et al in our group).

2) Carbon black support

Fig.2 shows the values of Idl, which corresponds to surface area of CB support, for various electrochemical treatment conditions.

While Idl decreased gradually with elevated temperature at 0.7V, it increased appreciably with temperature at 0.9V. These results suggest that corrosion mechanism of CB support at 0.9V differs from that at 0.7V. For example, by the corrosion at 0.9V, the surface of the CB might be roughened or the hydrophilic property of the CB might be increased.

before 200 220 240 treatment Temperature CC)

Fig.2 Double layer current (Idl) changes in catalysts treated under different temperatures and potentials for48hours

3) Electrode performance

Table 2 shows the preliminary results of electrode performance measurements for electrodes with catalysts before and after electrochemical treatment.

Table 2 Performances of the electrode

electrode

Terminal voltage (mV at 300mA/cm2, Air)

02 gain*** (mV)

Idl , (mA/cm2)

(Pt-cnr/cnr)

A*

0 0

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