Electrical Response of a New Lipophilic Ionic Liquid and the Effect of CO2 on Its Conductivity Mechanism
Authors: Bertasi Federico , Vezzù Keti , Pagot Gioele , Pace Giuseppe , Negro Enrico , Abu-Lebdeh Yaser , Armand Michel , Di Noto Vito 
Published: February 2020

Ionic liquids (ILs) have drawn sustained attention in the last twenty years due to their unique combination of intrinsic conductivity, very low vapour pressure and their ability to be tailored to an application via facile chemical modification [1].

As a consequence, the development of new ILs with improved properties and an in-depth understanding of the interplay existing between structures and properties are particularly active research fields.

In this report preparation and study of a new lipophilic tetraoctyl-formamidinium bis(trifluoromethanesulfonyl) imide (TOFATFSI) ionic liquid [2], will be discussed.

Tetraoctyl-formamidinium (TOFA) TFSI proved to be a water-insoluble IL that is completely miscible with the lower alkanes and the solutions are ionic conductors. Therefore, we were intrigued if conductivity could be induced in an even more demanding medium, i.e. supercritical carbon dioxide (scCO2) [3,4].

Following this, the conductivity and relaxation phenomena of this new IL are revealed through the analysis of the broadband electric spectra with a particular emphasis on the effect of temperature and CO2 pressure on the IL conductivity.

It is found that temperature boosts the conductivity via an increase in the charge carrier mobility. Also, CO2 absorption affects both the conductivity and the permittivity of the material due to the presence of CO2–IL interactions that modulate the nanostructure and the size of the TOFATFSI aggregates, which increases both the mobility and the density of the charge carriers.

Acknowledgements

The authors wish to thank the Strategic Project of the University of Padova “Materials for Membrane-Electrode Assemblies to Electric Energy Conversion and Storage Devices (MAESTRA)” for funding. V.D.N. thanks the University Carlo III of Madrid for granting him the “Catedra de Excelentia” (Chair of Excellence).

References

[1] F. Bertasi, K. Vezzù, G. Nawn, G. Pagot, V. Di Noto, Interplay Between Structure and Conductivity in 1-Ethyl-3-methylimidazolium tetrafluoroborate/(δ-MgCl2)f Electrolytes for Magnesium Batteries, Electroch. Acta, 219, 152-162 (2016).

[2] Federico Bertasi, Guinevere A. Giffin, Keti Vezzù, Pace Giuseppe, Yaser Abu-Lebdeh, Michel Armand, Vito Di Noto, A lipophilic ionic liquid based on formamidinium cations and TFSI: The electric response and the effect of CO2 on conductivity mechanism, PCCP, 19, 26230 – 26239 (2017).

[3] V. Di Noto, K. Vezzù, F. Conti, G.A. Giffin, S. Lavina, A. Bertucco. Broadband electric spectroscopy at high CO2 pressure: Dipole moment of CO2 and relaxation phenomena of the CO2 - poly(vinyl chloride) system. J. Phys. Chem. B, 115, 9014-9021 (2011).

[4] S. Kitajima, F. Bertasi, K. Vezzu’, E. Negro, Y. Tominaga, V. Di Noto. Dielectric relaxations and conduction mechanisms in polyether-clay composite polymer electrolytes under high carbon dioxide pressure. Phys. Chem. Chem. Phys., 15, 16626-16633 (2013).

Figure 1