In situ infrared spectroscopy at single-crystal metal electrodes: an emerging link between electrochemical and ultrahigh-vacuum surface science

Abstract

The utilization of infrared reflection-absorption spectroscopy for the in situ molecular characterization of monocrystalline metal-solution interfaces is outlined in comparison with the behavior of metal surfaces in ultrahigh vacuum (uhv) and illustrated for the adsorption of carbon monoxide on low-index platinum and rhodium surfaces in aqueous media. The effects of altering the electrode potential on the C-O stretching frequencies (vm) and terminal/bridging binding-site geometries are discussed in relation to similar spectral changes induced at metal-uhv interfaces by alterations in the local electric field and by the addition of dipolar and ionizable adsorbates. Quantitative links between these electrochemical and uhv-based phenomena are established by utilizing a common surface-potential scale. Interpretation of the various potential-induced spectral shifts is outlined in terms of alterations in the local electrostatic field and in the adsorbate-surface coordinate binding; the need to incorporate the latter phenomenon in order to account for the present experimental results is emphasized. The inherently coupled nature of the solvent dipolar and free charge contributions to the electrochemical surface potential is pointed out. The role of water and hydrogen coadsorption in the electrochemical systems is explored both on the basis of in situ infrared data and from related spectral observations at metal-uhv interfaces. Alterations in CO binding induced by metal coadsorption are briefly noted. The prospects for utilizing infrared spectroscopy to interconnect more generally the structural properties of related metal-solution and metal-uhv interfaces are discussed, along with the value of electrochemical systems for exploring fundamental issues relevant to both types of surfaces.

Site-dependent vibrational coupling of CO adsorbates on well-defined step and terrace sites of monocrystalline platinum: Mixed-isotope studies at Pt(335) and Pt(111) in the aqueous electrochemical environment

“…Absorbance spectra were then computed from the ratio of the sample and reference single beam spectra. The CO surface coverage was determined from the integrated absorbance of the solution 13 CO 2 and 12CO2 peaks at 2275 cm-1 and 6 2343 cm-1 , respectively [3,18,27]. Coverages are reported as a fraction of the saturation values ( 0 /0max).…”

“…Ref. [18,48]). Therefore, these conditions that promote extensive metal --2nt* backdonation, A final remark relates to the dilution limit frequencies, which shift higher in energy with increasing CO surface coverage in the electrochemical environment ( Figure 6 and Ref.…”

“…It is part of an effort in electrochemical surface science that aims to derive structural information on molecular adlayers at single crystal metal electrodes through comparative studies on corresponding surface/adsorbate systems in ultra high vacuum (UHV) [17,18]. Infrared spectroscopy has played a major role in supporting work in this area (see Refs.…”

“…Infrared spectroscopy has played a major role in supporting work in this area (see Refs. [17][18][19][20] for reviews). While the majority of these infrared spectroscopic studies have examined CO adsorption at the low index surface planes of platinum and rhodium, similar experiments using well-ordered high index surface planes of single crystal electrodes have recently appeared [3,4,[21][22][23], and work with Pt(335)/CO is the first of these to observe specific site-dependent phenomena [3,4].…”

In-Situ Electrochemical Surface Science

“…The latter may be ascribed to the effect of water (and in some cases hydrogen) coadsorption in the electrochemical systems [67).…”