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Figure 8.12 Relationships between the catalytic properties and electronic structure of Pt
3
M
alloys: correlation between the specific activity for the oxygen reduction reaction measured exper-
imentally by a rotating disk electrode on Pt
3
M surfaces in 0.1 M HClO
4
at 333 K and 1600 rev/min
versus the d-band center position for (a) Pt-skin and (b) Pt-skeleton surfaces. (Reprinted with
permission from Stamenkovic et al. [2007b]. Copyright 2007. Nature Publishing Group.)
catalytic activity being obtained for Pt
3
Co (Fig. 8.12) [Stamenkovic et al., 2007b]. The
overall consequence of this trend is that an active catalyst for the ORR should counter-
balance two opposing effects, namely, adsorption energy of O
2
and reaction inter-
mediates (O
2
,O
2
2
,H
2
O
2
, etc.), against the adsorption strength for spectator
oxygenated species. For metal surfaces that bind oxygen too strongly, as in the case
of Pt, the d-band center is too close to the Fermi level, and the rate of the ORR is lim-
ited by the availability of “spectator-free” (e.g., OH
ad
) Pt sites. On the other hand,
when the d-band center is too far from the Fermi level, as in the case of Pt
3
V and
Pt
3
Ti, the surface binds intermediates and O
2
too weakly to significantly promote
the ORR.
The success and great future potential of this approach was recently demonstrated
in our collaboration with Norskov's group, where our experimental results (summar-
ized in Fig. 8.12) and Norskov's componential screening of the same binary alloys
[Stamenkovic et al., 2006b] converge to the same optimal composition. This may
serve as a textbook example that the design of stable and catalytically active materials
for ORR electrocatalysis requires fundamental breakthroughs that come only from
basic research on well-characterized surfaces. However, even though it was tempting
to conclude that the rationale for the variation in activity depends exclusively on the
position of the metal d-states relative to the Fermi level, there is no proof that this is
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