Electrochemical and Raman spectroscopic investigations of butanol isomers at silver and gold electrodes.

摘要

The overall goal of this research is to characterize the solvent and electrolyte structure of the nonaqueous electrochemical double layer in the isomers of butanol on Ag and Au electrodes. Electrochemical and spectroscopic methods are employed to obtain structural information about the interface. In order to gain a better understanding of the Raman vibrational assignments of these alcohols, the Raman vibrational assignments were determined for a series of n-alcohols (n = 3-6, 8, 12, 14, and 18) in the spectral region from 700 to 1320 cm⁻¹ and 2800 to 3000 cm⁻¹. Solvent structure of the butanol isomers, 1-butanol, 2-butanol, and iso-butanol, were determined in-situ on rough Ag and Au electrodes using surface enhanced Raman scattering. Surface Raman selection rules were used to determine the average molecular orientation of these solvents at the electrode under potential control. The electrolyte structure in the nonaqueous electrochemical double layer has been determined using surface enhanced Raman scattering and differential capacitance measurements. Surface enhanced Raman scattering studies of the electrolyte structure were focused on probing the molecules solvating the cation and anion species, namely the alcohol and water impurity species. The ν(O-H) bands from these solvation species were monitored in these nonaqueous systems under potential control. These ν(O-H) bands distinctly describe the behavior of the LiClO₄, LiCl, LiBr, and LiI at the electrode under potential control. Differential capacitance measurements using an AC impedance method were performed to quantify anion coverages at smooth Ag electrodes in the butanol isomers. Cl⁻ and Br⁻ coverages were determined in the butanol isomers. This technique, coupled with SERS, provides complementary information about the electrolyte structure at the nonaqueous electrochemical double layer. The solvent and electrolyte structure is also determined ex-situ on emersed rough and smooth Ag and Au electrodes using Raman spectroscopy. Upon emersion of the electrodes into an inert Ar environment, solvent orientation and electrolyte behavior are investigated using Raman spectroscopy. These studies demonstrate both the utility of using Raman spectroscopy to probe emersed electrodes and the validity of emersing the electrode while preserving the double layer structure.