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have confirmed the CL shift for Pt-Co, even after electrochemical stabilization, by
using EC-XPS under the cleanest conditions.
For the Pt 60 Ru 40 alloy, however, the intensity of the Ru3d 5/2 and the binding
energy of the Pt4f 7/2 CL were unchanged after the potential sweeps. Therefore, it
can be concluded that the surface composition of the Pt 60 Ru 40 alloy was maintained
without any Ru dissolution in 0.05 M H 2 SO 4 solution during the potential sweeps
up to 0.80 V.
10.2.3.3 Change in the Electronic Structure of Pt by CO Adsorption
Figure 10.5 shows CO stripping voltammograms at these electrodes in N 2 -purged
electrolyte solutions measured in the EC chamber. The complete suppression of the
hydrogen desorption current at all the electrodes indicated a surface saturated with
CO. In the positive-going potential scan at the pure Pt electrode, a pre-oxidation
peak is seen between 0.50 and 0.70 V before a major CO oxidation peak at 0.73 V.
At the stabilized Pt-Co alloy electrode, the pre-oxidation peak is seen between 0.35
and 0.60 V, but the major CO oxidation peak appeared at the same potential as that
on the pure Pt. The onset potential for CO oxidation at the Pt-Ru alloy (0.35 V) is
the same as at Pt-Co, but the current rises steeply to reach the major peak at a lower
potential (0.52 V) than on Pt-Co or pure Pt. This is because CO oxidation at Pt sites
is facilitated by oxygen species adsorbed at Ru sites, i.e., through the bifunctional
mechanism. However, for the CO-tolerant HOR in the low potential region (E ,
0.1 V), the CO ad molecules are never oxidized, even at Pt-Ru, indicating that the
activity for the CO ad oxidation cannot be directly related to the CO-tolerant HOR
activity at such a low potential. Therefore, we focus on the interaction between
CO ad and these electrodes.
Figure 10.5 CO-stripping voltammograms (sweep rate 0.10 V s 21 ) at pure Pt and stabilized
Pt 58 Co 42 in 0.1 M HClO 4 , and Pt 60 Ru 40 in 0.05 M H 2 SO 4 at room temperature. The CO
pre-adsorption was performed in CO-saturated solution at 0.075 V for 5 minutes. (From
Wakisaka et al. [2006], reproduced by permission of the American Chemical Society.)
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