| As a non-aqueous solvent, room temperature ionic liquids (RTILs) have distinctadvantages, such as wide electrochemical window, vanishingly low vapor pressure, highconductivity, and other designable physical and chemical properties. RTILs have beenwidely used in various fields including electrochemistry. RTILs are composed pure ionsin the liquid state, which is different from the traditional aqueous or organic solvents.Therefore，deeper insight to the interfacial structure of “RTILs/metal electrode” is highdesired because it is beyond the description of classical electrochemical theory for thedilute aqueous electrolyte/metal electrode system. The investigation of the interfacialstructure of RTILs/metal electrode is beneficial to extend the application of RTILs.The high sensitive surface enhanced Raman spectroscopy (SERS) combined withelectrochemical methods provides a powerful tool for probing the adsorption of chemicalspecies and RTILs themselves. The information of the surface structure, properties, andadsorption behavior can be probed at the molecular level. The main results are outlinedas follows:1. To develop the proper electrochemical SERS technique for exploring of RTILs/metalelectrode system. By using4-cyanopyridines (4-CNPy) as probe, its adsorption behaviorwas resolved based at Pt or Au electrode based on SERS surface selection rules andelectrochemical Stark effect. The results showed that4-CNPy bounded to the Au surfacethrough the N atom of the Py ring in the slightly negative potential region. While in themore negative potential region, the4-CNPy molecules lay flat on the surface whichresulted in the decrease of surface coverage. In addition, a relative low Stark tuning ratein ionic liquid was measured by comparison to the aqueous systems. It was originatedfrom the unique RTILs/Au interfacial structure and the coadsorption of RTILs and 4-CNPy.2. In situ SERS investigation on adsorption behavior of [BMIM]SCN at [BMIM]BF4/Auelectrode was performed. It was found that [BMIM]SCN adsorbed on the Au surfacewithin a wide potential region. In the potential range of-0.4V to-0.8V, SCN-wasadsorbed mainly through S atom onto the Au electrode while in the range of-0.8V to-2.0V, it was oriented mainly through N atom. The effect of water on the reorientation ofionic liquids and SCN-was investigated. In this case, the increase of Stark tuning ratewas measured. The results showed that water may penetrate into the double layer of[BMIM]BF4/Au interface to affect the distribution of cation and anions.3. In the system of “[BMIM]BF4/Pt”, the electrochemical properties of CO and interfacestructure are studied through cyclic voltammetry with the change in the concentration ofwater. The onset potential of the CO oxidation negatively shifted with the increase of thewater concentration, suggesting that CO was oxidized more easily in [BMIM]BF4ionicliquid by the adding water, which acted as the source of oxygen atom. In addition, theintroduction of water resulted in the multi-adsorption configuration of CO, i.e. thecoexistence of linear and bridge adsorption. The increase of water concentrationmagnified the Stark tuning rate of CO in [BMIM]BF4solution4. The electrodeposition of Cu layer was preliminary investigated in [BMIM]BF4on ITOelectrodes by constant potential method. The composition and surface morphology of thedeposition layers were characterized, indicating that they were strongly depended on theapplied potentials. With negative movement of applied potential, the catalytic activity ofthe deposition layers in the reduction of p-nitrophenol to p-aminophenol increased. Byusing pyridine as probe, the SERS performance of the deposited layer was studied. Theresults revealed that the Cu film deposited at appropriate potential exhibited high SERSactivity and uniformity, which would be become a potential SERS substrate. |
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