An Electrochemical in Situ Surface-Enhanced Raman Spectroscopic Study of Carbon Monoxide Chemisorption at a Gold Core−Platinum Shell Nanoparticle Electrode with a Flow Cell

Abstract

The adsorption behavior of a CO adlayer at a Au core−Pt shell (Au@Pt) nanoparticle electrode as a function of CO coverage, partial pressure, and electrolyte composition is examined by electrochemical in situ surface-enhanced Raman spectroscopy (SERS) combined with a thin layer flow cell, which allows time-resolved spectro-electrochemical measurements upon sudden exchange of the electrolyte under potential control. We find (i) a clear decrease (increase) in the Pt−COL (C−OL) peak frequency and an increase of both bands’ intensities with COad coverage; (ii) a slight increase in the Pt−COL and decrease in the C−OL stretching frequencies and an increase in both intensities of the COad-saturated layer when switching from CO-saturated to CO-free solution; (iii) a clear decrease (up to 50%) of intensities of all of the Pt−CO and C−O bands and the SERS background during the solution switch from H2SO4 or NaOH to Na2SO4; (iv) a slightly higher C−OL (lower Pt−COL) peak frequency in H2SO4 than that in Na2SO4 and NaOH. The contributions of different factors such as SERS enhancement, Pt−CO binding strength, CO molecular orientation, and dynamic dipole−dipole coupling interactions among the COad molecules to the SERS spectral behavior are discussed on the basis of the complementary information of both Pt−CO and C−O stretching vibrations.