Cation Of Room Temperature Ionic Liquids Research Articles

Two-Component Electrolyte Solutions with Dipolar Cations on a Charged Electrode: Theory and Computer Simulations

The development of advanced electrochemical devices for energy conversion and storage requires fine tuning of electrode reactions, which can be accomplished by altering the electrode/solution interface structure. Particularly, in case of an alkali-salt electrolyte the electric double layer (EDL) composition can be managed by introducing organic cations (e.g. room temperature ionic liquid cations) that may possess polar fragments. To explore this approach, we develop a theoretical model predicting the efficient replacement of simple (alkali) cations with dipolar (organic) ones within the EDL. For the typical values of the molecular dipole moment ($2-4~D$) the effect manifests itself at the surface charge densities higher than 30 $\mu C/cm^2$. We show that the predicted behavior of the system is in qualitative agreement with the molecular dynamics simulation results.

Electrodeposition of Crystalline Aluminium on Carbon Steel in Aluminium Chloride — Trimethylphenyl Ammonium Chloride Ionic Liquid

Aluminium electrodeposition on carbon steel is performed potentiostatically and galvanostatically from aluminium chloride — trimethylphenylammonium chloride room temperature ionic liquid (RTIL). The influence of the electrochemical parameters and temperature on the coating composition, morphology and corrosion resistance is studied. For each experimental condition, the coatings are composed of metallic crystalline aluminium, contain a small amount of chlorine and a few RTIL cations remain weakly adsorbed on their surface. It is shown that temperature increase favors the growth of aluminium coating but to the detriment of the nucleation and well covering coatings. The galvanostatically formed coatings at low temperature present a corrosion resistance close to that of aluminium.

“One dimensional” double layer. The effect of size asymmetry of cations and anions on charge-storage in ultranarrow nanopores—an Ising model theory

We develop a statistical mechanical theory of charge storage in quasi-single-file ionophilic nanopores with pure room temperature ionic liquid cations and anions of different size. The theory is mapped to an extension of the Ising model exploited earlier for the case of cations and anions of the same size. We calculate the differential capacitance and the stored energy density per unit surface area of the pore. Both show asymmetry in the dependence on electrode potential with respect to the potential of zero charge, related to the difference in the size of the ions, which will be interesting to investigate experimentally. It also approves the increase of charge storage capacity via obstructed charging, which in these systems emerges for charging nanopores with smaller ions.

Understanding the wettability of nanometer-thick room temperature ionic liquids (RTILs) on solid surfaces

Many important applications of room temperature ionic liquids (RTILs), e.g., lubrication, energy storage and catalysis, involve RTILs confined to solid surfaces. In order to optimize the performance, it is critical to understand the wettability of nanometer-thick RTILs on solid surfaces. In this review, the recent progress in this filed is presented. First, the macroscopic wettability of RTILs on solids will be discussed briefly. Afterwards, the wetting of nanometer-thick RTILs will be discussed with the emphasis on RTIL/mica and RTIL/graphite interfaces since mica and graphite not only are mostly studied but also have important real-life applications. For RTIL/mica interface, the extended layering that promotes the wetting has been extensively reported and it is generally accepted that the electrostatic interaction at the RTIL/mica interface is the key. However, recent works from others and us highlight the unexpected effect of water: Water enables ion exchange between K+ and the cations of RTILs on the mica surface and thus triggers the ordered packing of cations/anions in RTILs, resulting in extended layering. Different from mica, there is no electrical charge on the graphite surface. Interestingly, previous reports showed inconsistent results on the wettability of RTILs on graphite. Recent research from others and us suggested that π-π+ stacking between sp2 carbon and the imidazoliumcation in the RTILs is the key to the extended layering and enhanced wettability of RTILs. Lastly, the future research directions will be briefly discussed.

Influence of humidity on performance and microscopic dynamics of an ionic liquid in supercapacitor

We investigated the influence of water molecules on the diffusion, dynamics, and electrosorption of a room temperature ionic liquid (RTIL), $[\mathrm{BMI}{\mathrm{m}}^{+}][\mathrm{T}{\mathrm{f}}_{2}{\mathrm{N}}^{\ensuremath{-}}]$, confined in carbide-derived carbon with a bimodal nanoporosity. Water molecules in pores improved power densities and rate handling abilities of these materials in supercapacitor electrode configurations. We measured the water-dependent microscopic dynamics of the RTIL cations using quasielastic neutron scatting (QENS). The ionic liquid demonstrated greater mobility with increasing water uptake, facilitated by the nanoporous carbon environment, up to a well-defined saturation point. We concluded that water molecules displaced RTIL ions attached to the pore surfaces and improved the diffusivity of the displaced cations. This effect consequently increased capacitance and rate handling of the electrolyte in water-containing pores. Our findings suggest the possible effect of immiscible co-solvents on energy and power densities of energy storage devices, as well as the operating viability of nonaqueous supercapacitor electrolytes in humid environments.

Allylic ionic liquid electrolyte-assisted electrochemical surface passivation of LiCoO2 for advanced, safe lithium-ion batteries.

Room-temperature ionic liquid (RTIL) electrolytes have attracted much attention for use in advanced, safe lithium-ion batteries (LIB) owing to their nonvolatility, high conductivity, and great thermal stability. However, LIBs containing RTIL-electrolytes exhibit poor cyclability because electrochemical side reactions cause problematic surface failures of the cathode. Here, we demonstrate that a thin, homogeneous surface film, which is electrochemically generated on LiCoO2 from an RTIL-electrolyte containing an unsaturated substituent on the cation (1-allyl-1-methylpiperidinium bis(trifluoromethanesulfonyl)imide, AMPip-TFSI), can avert undesired side reactions. The derived surface film comprised of a high amount of organic species from the RTIL cations homogenously covered LiCoO2 with a <25 nm layer and helped suppress unfavorable thermal reactions as well as electrochemical side reactions. The superior performance of the cell containing the AMPip-TFSI electrolyte was further elucidated by surface, electrochemical, and thermal analyses.

Solvent Free Lithium Molten Salt as Electrolyte of Lithium Secondary Battery

As an electrolyte of lithium ion battery (LIB), a lithium salt as conductive ion source, such as lithium hexafluorophosphate (LiPF6), is dissolved into an organic solvent, such as mixture of ethylene carbonate and dimethyl carbonate. The organic solvents do not only dissolve the lithium salts but form solid electrolyte interface to enable stable charge-discharge. The organic electrolytes have high specific conductivity and wide electrochemical window, which allows charge-discharge of 4V-class electrode materials. However, they are weak to heat in unexpected condition due to high vapor pressure and flammability of organic solvent.We have focused on the electrolyte lithium salts themselves and studied about a low-melting lithium molten salt electrolyte, which is composed of lithium cation and its counter anion for two aims. Firstly, the lithium molten salt has low-vapor pressure and non-flammability as same as the room temperature ionic liquids (RTILs). A battery using high-melting lithium molten salt, such as LiCl-KCl eutectic, is rugged and high storage property. It has been practically used at above 350 ºC.[1] The low-melting lithium molten salt enables the molten salt battery to be used for broad application similar to LIB. On the other hand, the lithium molten salt contains only lithium cation and the counter anion, that is, there is no organic solvents, organic cations of RTILs, and the other additive materials. Its properties are affected by only its counter anions. Thus, properties of this simple electrolyte are expected to be a base on the solvent-mixed electrolytes.Various lithium salts were synthesized and their melting point and thermal stability were investigated. Almost lithium perfluoro salts, such as LiPF6, which are used as the electrolyte lithium salts of LIB due to its high oxidative resistance, are not used as molten salts because they thermally decomposed before melting. Meanwhile, lithium perfluorosulfonylamides, such as lithium bis(trifluoromethylsulfonyl)amide, are respectively low-melting (below 250 ºC) and stable liquid temperature range (to above 300 ºC). In particular, lithium (fluorosulfonyl)(trifluoromethylsulfonyl)amide (Li[fTfN]) possesses a significantly low melting point (100 ºC) among the lithium salts due to asymmetric structure of fTfN anion.[2] Its single melt is also wide electrochemical window of 5.0 V from lithium metal deposition to oxidative decomposition of fTfN anion. Composite LiCoO2 or LiFePO4positive electrode and graphite negative electrode, which were prepared for the solvent-mixed electrolytes at room temperature, were successful in charge and discharge with the Li[fTfN] single molten salt at above 100 ºC.[3] Therefore, the Li[fTfN] can be used as a single lithium molten salt electrolyte without any organic solvents or RTILs. Reduced melting point, lower viscosity and higher specific conductivity have been attempted by addition to the other salts. These electrolyte properties and results of charge-discharge test will be presented.[1] P. Masset and R. A. Guidotti, J. Power Sources, 164, 397 (2007).[2] H. Matsumoto, N. Terasawa, T. Umecky, S. Tsuzuki, H. Sakaebe, H. K. Asaka, K. Tatsumi, Chem. Lett., 37, 1020 (2008).[3] K. Kubota and H. Matsumoto, J. Phys. Chem. C, 117,18829 (2013). Acknowledgements This work was supported by the ALCA program of Japan Science and Technology Agency (JST) and Grant in Aid for scientific Research from Japan Society for the Promotion of Science (JSPS).

Desorption process in room temperature ionic liquid based-mixtures under vacuum

A desorption process of room temperature ionic liquids (RTILs) based-mixtures is examined by monitoring the mass transfer and temperature under vacuum. Cations of RTILs are N, N-diethyl-N-methyl-N-(2-methoxyethyl) ammonium, [DEME], 1-ethyl-3-methylimidazolium, [C2mim], and 1-butyl-3-methylimidazolium, [C4mim]. Anions are tetrafluoroborate, [BF4], and bis(trifluoromethanesulfonyl)imide, [TFSI]. Additives for mixtures are H2O, D2O, CH3OH, C2H5OH, n-C3H7OH, i-C3H7OH, (CH3)2CO and C6H6. At the early stage of the desorption process under vacuum, transparent [DEME][TFSI]– and [C2mim][TFSI]–i-C3H7OH turned to be white homogeneously. Then, accompanying with drastic changes in the mass and temperature curves at the late stage, the mixtures become transparent again. At low-pressure, critical scattering as a precursor phenomenon of phase separation appeared only in [DEME][TFSI]– and [C2mim][TFSI]–i-C3H7OH. At room temperature and ambient pressure, different Raman spectra of a [TFSI] anion in [DEME][TFSI]–n-C3H7OH and –i-C3H7OH were observed in propanol-rich region. Therefore, the mixing states are drastically changed by respective propanol isomers.

Behavior of Short Nitroxide Biradical in Room Temperature Ionic Liquids

The intramolecular electron spin exchange in short nitroxide biradical O=S(OR6)2 (I), where OR6 is 1-oxyl-2,2,6,6-tetramethyl-4-oxypiperidine, dissolved in the room temperature ionic liquids (RTILs) 1-octyl-3-methylimidazolium hexafluorophosphate (omimPF6), 1-octyl-3-methylimidazolium tetrafluoroborate (omimBF4), 1-butyl-3-methylimidazolium tetrafluoroborate (bmimBF4), and 1-ethyl-3-methylimidazolium tetrafluoroborate (emimBF4) has been studied by electron paramagnetic resonance (EPR) spectroscopy as a function of temperature. Temperature variations of the isotropic nitrogen hyperfine splitting constant a were measured from EPR spectra. Thermodynamic parameters of the conformational rearrangements were calculated and compared with literature data. These intramolecular movements in rather rigid short-chain biradical I dissolved in four different RTILs are described well by the Debye–Stokes–Einstein law. Unrestricted density-functional-theory calculations of the geometry and electronic structure of the biradical were carried out using the ORCA program package, and showed that the O=S< group is available for the interaction with anions and cations of RTIL. The possible mechanism of such conformational transitions in biradical I in RTIL is discussed.

Hydrodynamic Interpretation on the Rotational Diffusion of Peroxylamine Disulfonate Solute Dissolved in Room Temperature Ionic Liquids As Studied by Electron Paramagnetic Resonance Spectroscopy

Rotational motion of a nitroxide radical, peroxylamine disulfonate (PADS), dissolved in room temperature ionic liquids (RTILs) was studied by analyzing electron paramagnetic resonance spectra of PADS in various RTILs. We determined physical properties of PADS such as the hyperfine coupling constant (A), the temperature dependence of anisotropic rotational correlation times (τ(∥) and τ(⊥)), and rotational anisotropy (N). We observed that the A values remain unchanged for various RTILs, which indicates negligible interaction between the N-O PADS group and the cation of RTIL. Large N values suggest strong interaction of the negative sulfonyl parts of PADS with the cations of RTILs. Most of the τ(∥), τ(⊥), and (τ(∥)τ(⊥))(1/2) values are within the range calculated on the basis of a hydrodynamic theory with stick and slip boundary conditions. It was deduced that this theory could not adequately explain the measured results in some RTILs with smaller BF(4) and PF(6) anions.

Effects of room-temperature ionic liquids on the chemical vapor generation of gold: Mechanism and analytical application

To get insight into the mechanism of the effect of room-temperature ionic liquids (RTILs) on the chemical vapor generation (CVG) of noble metals, gold was taken as a model element, and eight RTILs were examined. All the RTILs resulted in 3–24 times improvement in sensitivity for Au, depending on their nature. For the RTILs with identical anion, the RTILs with the cations of short chain exhibited better enhancement effect than those with long alkyl chain length or complex branch chain. For the RTILs with identical cation, the RTILs with Br − gave the best enhancement effect. The formation of ion pairs between the cation of RTILs and the anion species of gold via electrostatic interaction, and/or the substitution of the Cl − in the anion species of gold by the anion of RTILs likely enabled a more effective CVG reaction to occur. The RTILs also facilitated the generation of small bubbles and provided an electrostatic stabilization to protect the unstable volatile gold species and to help fast isolation of volatile gold species from the reaction mixture. 1-Butyl-3-methylimidazolium tetrafluoroborate [C 4mim]Br gave the best improvement in the sensitivity (24 times) among the RTILs studied, and also reduced the interferences from common transition and other noble metals. Based on the enhancement effect of [C 4mim]Br, a novel flow injection–CVG–atomic fluorescence spectrometric method with a detection limit (3 s) of 1.9 μg L −1 and a precision of 3.1% (50 μg L −1, RSD, n = 11) was developed for the determination of trace gold in geological samples.

Acute toxicity of oxygenated and nonoxygenated imidazolium‐based ionic liquids to Daphnia magna and Vibrio fischeri

Room-temperature ionic liquids (RTILs) recently have generated great interest as a result of their potential commercial applications. In particular, because of their negligible vapor pressure and low inflammability, they have been suggested as green alternatives to traditional organic solvents. The toxicity and potential environmental risk of this heterogeneous class of chemicals, however, are poorly understood. An alkyl-substituted RTIL, 1-butyl-3-methylimidazolium tetrafluoroborate ([bmim][BF(4)]), is one of the most widely used cations of RTILs, and information regarding its toxicity is relatively extensive. On the other hand, oxygenated chain-substituted ionic liquids, 1-methoxyethyl-3-methylimidazolium salts (moemims), are a new class of RTILs that have been poorly studied. Here, we compared the acute toxicity of [bmim][BF(4)] and moemims to the crustacean Daphnia magna (end point, 48-h immobilization) and the bacterium Vibrio fischeri (end point, 15-min inhibition of bioluminescence). The concentrations of [bmim][BF(4)] resulting in 50% of the maximum adverse effect (EC50s) for D. magna and V. fischeri were 5.18 and 300 mg/L, respectively, and were consistent with previously published values. The EC50s of the two moemims for D. magna are very similar, ranging from 209 to 222 mg/L in different experimental trials, and are higher by two orders of magnitude than the EC50 of [bmim][BF(4)]. The EC50s of 1-methoxyethyl-3-methylimidazolium tetrafluoroborate ([moemim][BF(4)]) and 1-methoxyethyl-3-methylimidazolium dicyanamide ([moemim][dca]) for V. fischeri are 3,196 and 2,406 mg/L, respectively. Results indicate that introduction of an oxygenated side chain in the imidazolium cation can greatly reduce the toxicity of RTILs and that these RTILs are less toxic than commonly used chlorinated solvents, such as tricloromethane, but are more toxic than nonchlorinated solvent, such as methanol and acetone.

Lithium Secondary Batteries Using Modified-Imidazolium Room-Temperature Ionic Liquid

Highly reversible, safe lithium secondary batteries that use imidazolium-cation-based room-temperature ionic liquid as an electrolyte and lithium metal as an anode material were realized by the molecular design. To achieve higher reduction stability, an electron-donating substituent was introduced to promote charge delocalization in the imidazolium cation of room-temperature ionic liquids.