In situ spectroelectrochemical studies of potential driven changes in the structure of the electrical double layer at the ionic liquid|electrode interface
Physical Chemistry of Solids and Surfaces, Material Characterisation
Final Report Abstract
Summarizing, this research project was realized successfully. The work plan of the project was well prepared and allowed in-time realization of individual research aims. First, amphiphilic cataions were used to fabricate thin organized films of ionic liquids (ILs) on a gold electrode surface. These ILs were synthesized in Chrisroffers groups and used in our preliminary studies. Our results showed that Langmuir-Blodgett transfer of ILs onto solid substrates leads to the anion exchange. Thus, a simple procedure of ion exchange in films of ILs was proposed in the literature. For further electrochemical studies imidazolium-based ILs were selected. To understand potential-driven changes in the composition and orientation of cations and anions of ILs in the electrical double layer in situ polarization modulation infrared reflection-absorption spectroscopy (PM IRRAS) with electrochemical control was used. We have shown that a film composed of a monolayer of imidazolium-based cations and adjacent anions (in the film or its vicinity) models well the electrode closest layer of the electrical double layer of ILs. Electric potentials cause movements of anions to and from the film and electrode surface. In contrast the imidazolium cation displays a titled toward the metal surface orientation, which does not change during the potential scan. Due to an excellent experimental approach, in which in situ PM IRRAS and x-ray photoelectron spectroscopy were used, we were able to describe these changes at a sub-molecular level. In the second part of the project realization ILs were pre-adsorbed on the electrode surface and introduced into the solution phase (electrolyte). To distinguish spectroscopically between IR spectra of the alkyl chains in ILs in the film and in the solution phase, for the needs of this research proposal, a per-deuterated 1-methyl-3-d37-octadecylimidazolium triflate [d37-C18Im]+[TfO]– has been synthesized in the Christoffers group. Our results show that in the vicinity of the electrode surface, the ILs both in the film and in bulk phase have an ability to form some complex aggregated structures. The composition of ions, the stability of the monolayer adjacent to the electrode surface, and the packing of cations and anions depend on the applied potential. These results demonstrate that the electric double layer of ILs is multicomponent and significantly extends above a monolayer or bilayer of well packed ions. Research of this research grant improved our understanding of dynamic changes in the electric double layer of ILs at a sub-molecular level. A similar experimental approach, dedicated to the studies of ILs containing cations which do not have ability to adsorb on the metal electrode surface appears as a continuation of this research. Such studies are rare in the literature and the electrical double layer other then imidazolium-based ILs is even less understood.
Publications
- ACS Sustainable Chemistry and Engineering, 7,2019,11593-11602. “Langmuir-Blodgett monolayers of partially fluorinated ionic liquids as twodimensional, more sustainable functional materials and coatings”
Sieling, T.; Christoffers, J.; Brand, I.
(See online at https://doi.org/10.1021/acssuschemeng.9b01496) - ChemElectroChem, 7, 2020, 3233-3243. “In situ spectroelectrochemical investigation of potential-dependent changes in an amphiphilic imidazolium-based ionic liquid film on the Au(111) electrode surface”
Sieling, T.; Brand. I.
(See online at https://doi.org/10.1002/celc.202000385)
