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 cyanide ions on Pt(lll) electrode in electrolyte solutions. Only a single absorption peak was observed at ca. 2100 cm(-1) in solutions containing H3O+, Li+, Na+, K+, or Cs+. In a KClO4 solution (pH = 9.5), a change 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 the cathodic region in the KClO4 solution, H3O+ dominates the outer Helmholtz plane as a result of cation exchange. In alkaline solutions, the slope for the frequency shift is dependent on the cations in the order 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 considered for interpreting the influence of this strongly adsorbed cation.