Broadband Sum Frequency Generation Studies of Surface Intermediates Involved in Fuel Cell Electrocatalysis - Fuel Cell Catalysis: A Surface Science Approach - page 383

Figure 12.11 (a) SFG spectra of atop CO on a Pt(111) electrode, with a 25 mm thick
CO-saturated 0.1 M H 2 SO 4 electrolyte and at a scan rate of 1 mV/s. Each displayed spectrum
resulted from a 15 s acquisition. Above 0.532 V, the atop intensity jumped and 3-fold sites
were converted to bridge sites. At 0.547 V, bridge and 3-fold CO coexist. (b) Spectrum of
atop CO in the (2 2)23CO (I) and (

p

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p

)R23.48213CO (II) adlayers. The broadband
IR BBIR pulses (dashed lines) were tuned to maximize atop (I) and the multiply bonded
(II) intensities (solid lines). In case (II), the much more intense atop transitions could
also be seen, despite being in the wings of the BBIR pulse spectrum. Data at 0.607 V show
simultaneous disappearance of atop and bridge-bonded CO.

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site occupancies but also the electronic polarizability of the Pt surface. The change in
surface properties is clearly evident in second-harmonic generation (SHG) measure-
ments, which are much more sensitive to the Pt surface than to the adsorbate
[Severson et al., 1995]. As we reported [Lagutchev et al., 2006], the problem using
SFG to determine coverage changes during a surface transformation is that the SFG