In situ spectroelectrochemical studies of potential driven changes in the structure of the electrical double layer at the ionic liquid|electrode interface

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The properties of room-temperature ionic liquids ((RTILs), a pure ionic solvent with potential window of 3-6 V) are very attractive for their applications as electrolytes in electrochemical systems, as solvents for studies of complex redox reactions or as supercapacitors. By contrast to conventional media in which molecules of a solvent and ions of a supporting electrolyte are in a direct contact with an electrode, in RTILs only ions are present on the electrode surface. It influences the macroscopic electrochemical properties and structure of the electrical double layer of RTILs comparing to solvents commonly used in electrochemistry. Despite the fact that little is known about the structure of the electrical double layer of RTILs at a sub-molecular level, in situ studies of the electrical double layer of RTILs are very rare. In this project the structure of the electrical double layer of RTILs will be studied using electrochemistry and polarization modulation infrared reflection-absorption spectroscopy (PM IRRAS) under electrochemical control. According to recent findings (Kirchner et al., Electrochim.Acta.,110,2013,762) the supramolecular structure of the electrical double layer of RTILs depends on the potential applied to the electrode and varies from multilayer to monolayer assemblies. In this project Langmuir-Blodgett (LB) films mimicking the composition and structure of the electrical double layer of RTILs will be prepared on the surface of Au and Pt electrodes. Electrochemical potential window of the film adsorption, potential of zero charge and surface charge as the function of the electrode potential will be studied in LB films in aqueous and RTIL solutions. PM IRRAS under electrochemical control will be used to study impact of the potential applied to the electrode on the structure and orientation of anions and cations at the model RTIL|electrode interface. Next, in situ PM IRRAS will be used to investigate potential-driven changes in the structure and orientation of ions in the electrical double layer of pure RTILs. A differentiation of the IR absorption signals from the RTIL ions present in the bulk liquid phase from the ions adsorbed on the electrode surface is the main challenge of this research project. It will be possible only for such settings of the spectroelectrochemical cell in which the intensity of the p-polarized light (brings information on the ions adsorbed in the electrode surface and in the environment of the sample (electrolyte)) and the intensity of the s-polarized light (brings information about the environment of the sample) are the same. This smart experimental approach ensures a successful realization of this project and enlarges the applicability of the PM IRRAS as structure and surface analyzing technique.