The vibrational spectrum of carbon monoxide, exerted by dissociation of formic aid, has been investigated at the platinum electrode as a function of applied potential by using the surface-enhanced Raman spectroscopy (SERS) technique. The electrolyte is 0.1M LiClO4. Two typical SERS features observed at 475-490 and 2055-2080 cm-1 are attributed to the platinum-CO (Pt-C) and intramolecular C-O (C-O) stretching vibration, respectively, indicating linearly adsorbed CO on platinum. Comparisons of the present data with previous studies in aqueous solutions show that solution components, particularly the dielectric in the inner double layer, may significantly influence the interaction of CO with platinum, especially the CO intramolecular mode. Electrooxidation of CO was observed to occur at potentials more positive than 0.6 V, being slightly negative relative to previous studies for CO on smooth platinum, suggestive of a higher electrocatalytic activity for the present highly roughened platinum surface. At positive and moderately negative potentials (-0.2 to 0.6 V), the Pt-C and CO intramolecular bands exhibit opposite frequency changes with decreasing potential, with Stark tuning rate being -6 and 24 cm-1/V, respectively. At more negative potentials, both

Surface-enhanced Raman scattering from a silver electrode in solution of 0.1 M LiClO4 in acetonitrile has been analyzed as a function of applied potential. Three m (O-H) bands associated with the interfacial water and two m (O-H) bands associated with the OH ion species were observed depending on the electrode potential. The band at 3487cm 1 is favored at relatively positive potentials and assigned to H2O molecules interacting with the electrode surface via the oxygen atoms. Another band at 3586cm 1 appears in a wider potential region and is assigned to the H2O molecules with one or both of the hydrogen atoms facing the electrode surface. Additionally, evidence for the possible surface ion pair, Li

Surface-enhanced Raman scattering (SERS) from the platinum electrode-acetonitrile interface in the presence of iodide, the lithium cation, water, and pyridine was analyzed as a function of applied potential. It was found that the typical Raman band of cyanide species by the dissociation of the solvent acetonitrile upon adsorption onto highly roughened platinum electrode surfaces was detectable for all of the systems that were studied. However, the onset potential of the dissociation reaction of acetontrile differed for the four systems. We assume that competitive adsorption may exist between each of the above four species and the solvent acetonitrile molecule, especially at the dissociation reaction-active sites of the Pt surface. This competitive adsorption therefore significantly inhibits the decomposition reaction of acetonitrile. The interactions of these adsorbates with Pt are assumed to weaken in the sequence pyridine > I-> water Li+ on the basis of the observations of different negative shifts of the onset potential of acetonitrile decomposition. For the system with water or iodide, double-band character for the CN band was also detected. It is assumed to be due to the existence of two types of adsorbed ion pairs at the Pt surface: CN-…CH3CN and CN-…Li+/Na+.

The vibrational spectrum of carbon monoxide at the Pt/acetonitrile interface as a function of applied potential has been investigated using the surface-enhancedRamanspectroscopy technique. The electrolyte is 0.1 M LiClO4. The bands observed at ca. 506 and 2055 cm-1 are attributed to the platinum-CO (Pt-C) and intramolecular C-O (C-O) stretching vibrations, respectively, suggesting linearly adsorbed CO on platinum. The (Pt-C) band has an experimental Stark tuning rate of-4 cm-1/V, while the slope of (C-O) band frequency versus potential approaches zero before the onset of electro-oxidation ofCOads, possibly resulting from low surface coverage ofCOon platinum. The roughened Pt electrode surface has a high electrocatalytic activity, on whichCOelectro-oxidation occurs at ca.-0.7V(vs Ag/Ag+). The main product ofCOads oxidation is confirmed to be carbonate due to the existence of trace water in the double-layer region as a source of oxygen for the reaction. It has also been found that the solvent acetonitrile can exert a chemisorbed decomposition reaction on the roughened Pt surface, while the adsorption of CO can significantly inhibit this reaction.

Surface-enhanced Raman scattering (SERS) spectrum of imidazole adsorbed at a silver electrode in nonaqueous acetonitrile solution has been investigated as a function of applied potential. The electrolyte is 0.1M LiClO4. Results show that imidazole adsorbs on silver as a neutral molecule via the pyridine nitrogen atom. Coadsorption of perchlorate anion with imidazole, possibly by forming intermolecular hydrogen bonding, is also suggested by the enhancement of the ClO4-band at 933 cm-1. An edge-on orientation of imidazole at more positive potentials is proposed by the observation of the increase in frequency of the ring breathing modes, along with the enhancement of most of the in-plane modes of imidazole. When the potential is made more negative, particularly near -0.5V, the imidazole ring may change from vertical to be slightly inclined to the silver surface at an intermediate angle from the surface normal. At the same time, a slight rotation of the imidazole ring plane may occur, evidenced by the observation of the changes in relative intensity of