Broadband Sum Frequency Generation Studies of Surface Intermediates Involved in Fuel Cell Electrocatalysis - Fuel Cell Catalysis: A Surface Science Approach - page 369

& CHAPTER 12
Broadband Sum Frequency Generation
Studies of Surface Intermediates
Involved in Fuel Cell Electrocatalysis
G. Q. LU, A. LAGUTCHEV, T. TAKESHITA, R. L. BEHRENS,
DANA D. DLOTT, and A. WIECKOWSKI
Department of Chemistry, University of Illinois at Urbana-Champaign, Urbana, IL 61801, USA
12.1 INTRODUCTION
In this chapter, we discuss the use of broadband multiplex vibrational sum frequency
generation (BB-SFG) spectroscopy to study electrochemical interfaces [Lu et al.,
2005; Lagutchev et al., 2006]. In all vibrational SFG techniques, visible and vibra-
tional infrared (IR) pulses are incident simultaneously on the sample of interest, and
a coherent sum frequency signal in the visible range is produced (see Figs. 12.1 -
12.3) (Plate 12.1). In BB-SFG, as opposed to conventional (first-generation) SFG,
where spectra are obtained point-by-point, the entire spectral range spanned by the
IR pulse spectrum is probed simultaneously. In SFG, attenuation of the infrared
beam by the electrolyte is less of a concern than in IR reflection absorption spec-
troscopy (IRAS), since the infrared beam need not double-pass the electrolyte in
SFG. SFG is a well-known spectroscopic technique [Shen, 1989; Guyot-Sionnest
and Tadjeddine, 1990; Bonn et al., 2001] and the subject of several reviews
[Tadjeddine, 2000; Shen, 1994; Eisenthal, 1992; Richmond, 2002; Chen et al.,
2002]. There have been a few works prior to our studies where first-generation
SFG has been applied to electrochemical interfaces [Lu et al., 2004, 2005;
Lagutchev et al., 2006; Guyot-Sionnest and Tadjeddine, 1990; Guyot-Sionnest,
2005; Guyot-Sionnest et al., 1987; Chou et al., 2003a, b; Hoffer et al., 2002]. This
chapter is focused on the use of BB-SFG (second- and third-generation SFG) to
study electrochemical interfaces.
An SFG signal exhibits characteristic features at frequencies of molecular
vibrational resonances similar to the vibrational fingerprints of conventional IR