Infrared spectroelectrochemical study of cyanide adsorption on palladium surfaces

In situ FTIR spectroscopy is employed to study the adsorption of cyanide ion (CN-ads) within the double-layer region on a polycrystalline palladium surface in aqueous perchlorate (0.10 M NaClO4) electrolyte. Four surface infrared bands in the 1800-2200-cm-1 range are observed. Surface bands with peak maxima seen at about 2060 and 1980 cm-1 are assigned to linear and bridge-bound CN-ads, respectively. Two additional bands near 2150 and 2200 cm-1 are attributed to Pd/CN surface films. The relative intensities of the bands due to linear and bridged CN-ads suggest the predominance of the bridge-bound adsorbate on palladium. The experimentally observed frequency potential dependence (dνC-N/dE) for the bridged cyanide adsorbate (20 cm-1 V-1) is greater than that for the linearly adsorbed species (12 cm-1 V-1). Potential dependencies of the infrared frequencies due to linear and bridged CN-ads show little variation with changes in cyanide concentration. Possible explanations for the predominance of bridged bonding are given, along with a discussion of the formation and depletion of surface Pd/CN films. A classical theoretical model, employed previously in the analysis of adsorbed carbon monoxide on platinum, is used to estimate frequencies and potential dependencies of the C-N stretch for linear and bridged CN-ads on a palladium surface. © 1991 American Chemical Society.