Electrode/electrolyte interphase study using polarization modulated ftir reflection-absorption spectroscopy

Abstract

Polarization modulated Fourier transform infrared reflection-absorption spectroscopy (FT-IRRAS) is applied to the studies of adsorption and oxidation of CO on a platinum electrode in 0.5 M sulfuric acid and of adsorption of cyanide on gold and silver electrodes in 0.5 M potassium sulfate. The absorption intensity of the CO on platinum electrode is ~ 4-5% while that of the CN- on silver and gold is 0.2-0.5%. The potential dependence of the vibrational spectra was observed for both systems. Oxidation of the linearly adsorbed CO layer proceeds by different mechanisms depending on whether CO was adsorbed at a potential in the double-layer region or in the hydrogen region, i.e. at the edges of the CO islands in the former case and randomly in the latter case, in which the bridged CO species plays an important role. The vibrational frequency of the linearly adsorbed CO changes linearly with potential at a rate of 30 cm-1/volt, which is independent of anion specific adsorption. The origin of the shift is most reasonably explained by the first-order Stark effect. For Ag/CN- and Au/CN- systems, the surface cyanide species is assigned as linearly adsorbed CN . The anodic reaction products in the solution from cyanide ions and the electrode metals are also observed in the vibrational spectra. The bands due to surface species and those due to solution species are distinguished by measuring the spectra with s- and p-polariz.ed light. © 1984.