Surface-Enhanced Raman Scattering at the Silver Electrode/Ionic Liquid (BMIPF6) Interface

Publisher Website
Google Scholar
Abstract
This is the first report of in situ SER spectra of chemical species adsorbed on a Ag/room temperature ionic liquid (RTIL) interface. We have investigated the dependence of the SERS intensity of the RTIL derived from 1-n-butyl-3-methylimidazolium hexafluorophosfate (BMIPF6) adsorbed on a silver electrode. It has been shown that the BMI+ adsorbs on the silver electrode for potentials more negative than −0.4 V vs a Pt quasireference electrode (PQRE). In the −0.4 to −1.0 V potential range the SER spectra are similar to the Raman spectrum of the RTIL BMIPF6. At potentials more negative than −1.0 V some imidazolium ring vibrational modes and N−CH3 vibrations are enhanced, suggesting that the imidazolium ring is parallel to the surface and for potentials <−2.8 V the BMI+ is reduced to the BMI carbene. The potential dependence of the SERS intensities of Py adsorbed on a silver electrode in BMIPF6 has also been investigated. The results have shown that at potentials less negative than −0.8 V (vs PQRE) Py adsorbs at an end-on configuration forming an Ag−N bond. In the −0.9 to −1.4 V potential range Py molecules lie flat on the electrode surface and at potentials <−1.4 V Py is replaced by the BMI+. The electrochemical and SERS results have shown that Py has the effect of changing the oxidation of silver in that medium as well as the reduction of BMI+ to the BMI carbene. In the presence of Py the BMI+ reduction is observed at potentials near −2.4 V. The Ag electrode has presented SERS activity from 0.0 to −3.0 V.