Vitor L. Martins

Influence of the water content on the structure and physicochemical properties of an ionic liquid and its Li+ mixture.

The effect of water on the hydrophobic ionic liquid (IL) 1-n-butyl-2,3-dimethylimidazolium bis(trifluoromethanesulfonylimide) and its Li(+) mixture was evaluated. The electrochemical stability, density, viscosity, and ionic conductivity were measured for both systems in different concentrations of water. The presence of Li(+) causes a large increase in the water absorption ability of the IL. The experimental results suggest a break of the interactions between Li(+) and Tf2N(-) anions in the strong aggregates formed in dried Li(+) mixtures, modifying the size and physicochemical nature of these aggregates. It is also observed that the size of the ions aggregates with formal charge increases at high temperature and decreases the mobility of the charge carrier, explaining the break in the Walden rules at high temperature. Raman spectroscopy and molecular dynamic simulations show the structural change of these systems. In neat ILs, the water molecules interact mainly among each other, while in the Li(+) mixtures, water interacts preferentially with the metallic cation, causing an important change in the aggregates present in this system.

Physicochemical Properties of Three Ionic Liquids Containing a Tetracyanoborate Anion and Their Lithium Salt Mixtures

Given their relevant physicochemical properties, ionic liquids (ILs) are attracting great attention as electrolytes for use in different electrochemical devices, such as capacitors, sensors, and lithium ion batteries. In addition to the advantages of using ILs containing lithium cations as electrolytes in lithium ion batteries, the Li(+) transport in ILs containing the most common anion, bis(trifluoromethanesulfonyl) imide anion ([Tf2N]), is reportedly small; therefore, its contribution to the overall conductivity is also low. In this work, we describe the preparation and characterization of two new and one known IL containing the tetracyanoborate anion ([B(CN)4]) as the anionic species. These ILs have high thermal and chemical stabilities, with almost twice the ionic conductivity of the [Tf2N] ILs and, most importantly, provide a greater role for the Li(+) ion throughout the conductivity process. The experimental ionic conductivity and self-diffusion coefficient data show that the [B(CN)4]-based ILs and their Li(+) mixtures have a higher number of charge carriers. Molecular dynamics simulations showed a weaker interaction between Li(+) and [B(CN)4] than that with [Tf2N]. These results may stimulate new applications for ILs that have good Li(+) transport properties.

Electrochemical behavior of iron and magnesium in ionic liquids

In this work, the electrochemical behavior of Mg and Fe in ionic liquids (IL) were studied. We performed a series of cyclic voltammetry experiments to improve the understanding of Mg behavior in an IL containing the bis(trifluoromethanesulfonylimide) ([Tf2N]) anion. The results show an irreversible deposition/dissolution of Mg at a high water concentration (ca. 1300 ppm, 50 mmol L-1) and very low reversibility (7.3%) at a moderate water concentration (ca. 65 ppm, 5 mmol L-1). The formation of a film on the electrode surface and the presence of Mg were confirmed by scanning electron microscopy and energy-dispersive X-ray spectroscopy (SEM-EDS). The process irreversibility indicates the formation of a passivating film. Because the presence of water affects the reversibility of the process, studies of Fe deposition/dissolution were conducted in two different ILs and with microelectrodes to evaluate how the water modifies the reversibility and the diffusion of ions. Water plays an important role in the reversibility of Fe deposition/dissolution being that deposition is less reversible when water is absent. The Fe diffusion is also modified because the Fe ion coordination sphere is strongly affected by the presence or absence of water; the Fe diffusion was also shown to depend on the coordination ability of the cation.

Electrochemistry of copper in ionic liquids with different coordinating properties

The electrochemical behavior of Cu was evaluated in two different ionic liquids (ILs) that had the same piperidinium-based cations but different anions with different coordinating properties: bis(trifluoromethanesulfonylimide) ([Tf2N]) (strong coordinating property) and tetracyanoborate ([B(CN)4]) (weak coordinating property). Cyclic voltammetry and electrochemical impedance spectroscopy showed that the electrochemical behavior of Cu depends strongly on these coordinating properties. In the strongly coordinating IL, Cu exhibits no passivation, but a passivating film is formed on the metal surface in the weakly coordinating IL. Scanning electron microscopy indicated that Cu suffered from pitting corrosion in the presence of the strongly coordinating IL. Raman spectroscopy elucidated the formation of a thin film of Cu2O in both ILs, due to the trace presence of H2O (below 70 ppm). In the [Tf2N]-based IL, a Cu salt forms with the IL as the potential increases, but it is not enough to passivate the metal due to the solubility of the salt in the IL. In the [B(CN)4]-based IL, even at lower potentials, a Cu[B(CN)4] layer is formed that passivates the metal.

CHAPTER 13:Tailoring Transport Properties Aiming for Versatile Ionic Liquids and Poly(Ionic Liquids) for Electrochromic and Gas Capture Applications

Ionic liquids (ILs) and poly(ionic liquid)s (PILs) are known for their interesting characteristics, such as intrinsic ionic conductivity, high chemical, electrochemical and thermal stabilities, and low volatility. They constitute a versatile class of materials whose structure can be modified to yield a task-specific material with improved performance for a desired application. The physicochemical properties related to ionic transport can be tailored by modifying the cation and/or anion structure in addition to the polymeric matrix and spacer groups in the case of PILs. The properties can be improved for use in electrolytes and polymeric electrolytes for electrochemical devices such as rechargeable batteries and supercapacitors. ILs and PILs that possess good transport properties can be further functionalized to have electrochromic groups attached to their structure to construct electrochromic devices. In addition, these materials also present high selectivity for CO2 absorption, and can be modified to improve the capture capacity and separation efficiency. In this chapter, different aspects regarding the modification of ILs and PILs for different applications will be explored with a focus on the relationship between their structures and physicochemical properties, and the effect on their performance in different devices.