In situ infrared spectroscopy of the electrode—electrolyte interface

In the study of electrochemical processes, it is important to have a means for characterizing the molecular and ionic species at the electrode-electrolyte interface. Various types of optical vibrational spectroscopy are being used to do this in situ. Of these, Fourier transform infrared reflection absorption spectroscopy (IRRAS) has seen rapid progress and is in wide use. A review of the techniques used in our laboratory and examples of recent measurements are presented. The adsorbed species discussed are CO, CN
⁻
, SO
4
^2-
, and HSO
4
⁻
, and the electrodes are, in most cases, polycrystalline noble metals. It is shown how the interpretation of the infrared spectra is greatly aided by comparison with ab initio molecular orbital computations of ions and molecules on metal clusters. Some of the difficulties in the interpretation of the infrared spectra are illustrated, and the future development of optical vibrational spectroscopy for studying electrode-electrolyte interfaces is discussed.