CATION EFFECTS ON INFRARED REFLECTION-ABSORPTION SPECTRA OF CYANIDE ADSORBED ON PT(111) ELECTRODE IN ELECTROLYTE-SOLUTIONS

In-situ infrared reflection absorption spectroscopy was applied to the investigation of cation effects on the C-N stretching frequency of cy anide ions on Pt(lll) electrode in electrolyte solutions. Only a singl e absorption peak was observed at ca. 2100 cm(-1) in solutions contain ing H3O+, Li+, Na+, K+, or Cs+. In a KClO4 solution (pH = 9.5), a chan ge in slope was observed in the peak frequency-potential curve at ca. -0.5 V vs. the saturated calomel electrode. It was concluded that in t he cathodic region in the KClO4 solution, H3O+ dominates the outer Hel mholtz plane as a result of cation exchange. In alkaline solutions, th e slope for the frequency shift is dependent on the cations in the ord er K+ > Na+ > Li+ approximate to Cs+. In HClO4, a change in slope was also observed in the peak frequency-potential curve. In a Mg(ClO4)(2) solution, three peaks were observed for CN on Pt(lll), indicating that factors other than the simple electrochemical Stark effect must be co nsidered for interpreting the influence of this strongly adsorbed cati on.