Broadband Sum Frequency Generation Studies of Surface Intermediates Involved in Fuel Cell Electrocatalysis - Fuel Cell Catalysis: A Surface Science Approach - page 395

Figure 12.21 BB-SFG spectra of CO on a mixed metal electrode (in a CO-saturated 0.1 M
H 2 SO 4 solution) made by depositing Ru nanoislands on Pt(111) at a coverage of 0.35 ML.
The electrolyte is a 25 mm thick solution layer (see Fig. 12.1). The acquisition time was 40 s;
data were obtained at E ¼ 0.1 V. As in Fig. 12.11b(II), the BBIR pulses are tuned to optimize
the multiply bonded spectra, suppressing the atop intensity.
“metallic,” and the added Ru amounts are functionally causing the suppression of
back-donation of CO bonding on all surface sites [Tong et al., 2002]. (A sequence
of structural properties is then activated: the reduction in back-donation weakens the
metal - carbon bond, leading to a strengthening of the C - O bond, which, in turn,
gives rise to a blueshift in the CO stretching frequency, particularly well seen on
Ru-CO [Friedrich et al., 2002].) As the CO in the NMR measurements is just a surface
probe of the state of the electrode surface, the likely surface additive that accepts a den-
sity of states from both Pt and Ru on the ruthenated Pt surfaces [Tong et al., 2002] is
oxygen [Lewera et al., 2007] trapped between subsequent Ru layers deposited on Pt.
The surface science literature [Stampfl et al., 1996; Bottcher et al., 1997; Todorova
et al., 2002] documents thermally activated subsurface O present on Ru and/or Ru sur-
face oxide formation, especially at high oxygen pressure. The oxygen incorporated
into Pt(111)/Ru could easily function in a manner similar to Se adatoms deposited
on Ru particles (as a sink of the electronic charge (DOS) [Babu et al., 2007]), and
modify the properties of the Pt/Ru edge. At higher Ru coverage, the edge apparently
no longer serves as an efficient barrier against CO entering the Ru domains [Lu et al.,