Pure Room Temperature Ionic Liquids Research Articles

From Molecular Simulations to Experiments: The Recent Development of Room Temperature Ionic Liquid-Based Electrolytes in Electric Double-Layer Capacitors.

Due to the unique properties of room temperature ionic liquids (RTILs), most researchers' interest in RTIL-based electrolytes in electric double-layer capacitors (EDLCs) stems from molecular simulations, which are different from experimental scientific research fields. The knowledge of RTIL-based electrolytes in EDLCs began with a supposition obtained from the results of molecular simulations of molten salts. Furthermore, experiments and simulations were promoted and developed rapidly on this topic. In some instances, the achievements of molecular simulations are ahead of even those obtained from experiments in quantity and quality. Molecular simulations offer more information on the impacts of overscreening, quasicrowding, crowding, and underscreening for RTIL-based electrolytes than experimental studies, which can be helpful in understanding the mechanisms of EDLCs. With the advancement of experimental technology, these effects have been verified by experiments. The simulation prediction of the capacitance curve was in good agreement with the experiment for pure RTILs. For complex systems, such as RTIL-solvent mixtures and RTIL mixture systems, both molecular simulations and experiments have reported that the change in capacitance curves is not monotonous with RTIL concentrations. In addition, there are some phenomena that are difficult to explain in experiments and can be well explained through molecular simulations. Finally, experiments and molecular simulations have maintained synchronous developments in recent years, and this paper discusses their relationship and reflects on their application.

Effects of Operating Temperature on Li-O2 Battery with Ionic Liquid-Based Binary Electrolyte

The progress of rechargeable Li-O2 battery (LOB) is hampered due to the number of challenges its components present. Among various critical challenges, the choice of electrolyte has always been a bottleneck impeding the breakthrough in the development of LOB. Various electrolytes, including organic solvents and room-temperature ionic liquids (RTILs) have been developed and studied. Each electrolyte comes with various limitations, which restrict its application in the LOB. These include thermal and electrochemical stability, volatility, viscosity, flammability, capability to dissolve incoming oxygen, diffusivity, and ionic conductivity. Consequently, no electrolyte could be regarded as an ideal electrolyte. Nonetheless, efforts have been made to tune the physiochemical properties of the electrolyte by blending two or more miscible solvents. High thermal and electrochemical stability and negligible volatility of RTILs can be combined with high diffusivity and ionic conductivity of organic solvents by merely blending them with optimized volume ratios.In this study, we comprehensively investigated the effects of operating temperature (20°C, 40°C and 60°C) on the electrochemical performance of LOBs incorporated with RTIL and organic solvent binary electrolyte. We designed and investigated, 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide ([C2C1im][Tf2N]) RTIL and dimethyl sulfoxide (DMSO) organic solvent at various volume ratios ((4:1), (1:1), (1:4)). Among the binary electrolytes, ([C2C1im][Tf2N]/DMSO (1:4)) delivered the highest discharge capacities of 3.70 Ah g-1 (20°C), 4.0 Ah g-1 (40°C) and 3.65 Ah g-1 (60°C) as compared with pure [C2C1im][Tf2N] and DMSO. Cycling stability tests showed superior stability of the binary electrolyte ([C2C1im][Tf2N]/DMSO (1:4)) irrespective of the operating temperature. From viscosity and ionic conductivity measurements (at 20-60°C), [C2C1im][Tf2N]/DMSO (1:4) exhibited the highest ionic conductivity and the lowest viscosity compared with other binary electrolytes and pure RTIL at any given temperature. Cyclic voltammetry (CV) tests revealed a higher reaction rate with [C2C1im][Tf2N]/DMSO (1:4) binary electrolytes than pure electrolytes. The superior performance of [C2C1im][Tf2N]/DMSO (1:4) binary electrolyte was ascribed to enhanced stability against reactive intermediate species during oxygen reduction reaction (ORR), increased ionic conductivity, low viscosity (comparable with organic electrolytes), improved oxygen solubility, and relatively low evaporation rates. The detailed results and discussion will be presented during the presentation.

Ionic liquid derived novel deep eutectic solvents as low viscous electrolytes for energy storage

This work investigates a newly emerging class of solvents to be used as alternatives to or complementarily with ionic liquid (IL) electrolytes. Three novel deep eutectic solvents (DESs) comprised of the hydrogen bond donors (HBDs), namely N-Methylacetamide (NMAc) and formamide, were formulated with three variants of the methyl imidazolium-based ionic liquids (ILs) as hydrogen bond acceptors (HBAs). ILs consisting of 1-butyl-3-methyl imidazolium ([BMIM]) cation with anions namely methanesulphonate ([MeSO3]), bis(trifluoromethylsulfonyl)imide ([Tf2N]), and hexafluorophosphate ([PF6]) were used as hydrogen bond acceptors. Initially, the eutectic points of the DESs were estimated using a quantum chemical-based thermodynamic model, namely Conductor like Screening Model-Segment Activity Coefficient (COSMO-SAC). The calculated melting points of the DESs were determined to be markedly lower than those of both the constituent components. Further, physical and chemical characterization was done on the synthesized DESs. The viscosities (<20 cp) were found to be significantly lower than those of conventionally used pure room temperature ILs, and ionic conductivities (>5 mS/cm) were found to be appreciably higher than those of the corresponding constituent ILs. Thermogravimetric analysis revealed negligible mass loss up to 80–100 °C. Linear scan voltammetry (LSV) was employed to determine the electrochemical stable potential window (ESPW) of the solvents with a glassy carbon (GC) electrode. LSV provided electrochemical stabilities in the range of 3.8–4 V for all three studied deep eutectic solvents, comparable to pure ILs and far higher than the potential windows of mixtures of ILs and organic solvents, a blend commonly used as electrolytes.

Fluoride-free electropolymerization of 3-aminophenylboronic acid in room temperature ionic liquids without exogenous protons

The electropolymerization of 3-aminophenylboronic acid (3-APBA) in conventional electrolyte usually requires fluoride and an exogenous proton source to obtain high quality poly-3-aminophenylboronic acid (Poly (3-APBA)). In the present work, the direct electropolymerization of 3-APBA in neat room temperature ionic liquids 1-butyl-3-methylimidazolium hexafluorophosphate ([BMIM]PF6) is investigated for the first time. Without fluoride or exogenous proton, Poly (3-APBA) is indeed obtained. The imidazolium-based ionic liquids [BMIM]PF6 acts as the supporting electrolyte. The PF6− acts as a hybridization agent and the imidazolium rings act as the dopants. Each ion is involved in the electropolymerization process and plays an important role. Electrochemical measurements indicate that the obtained Poly(3-APBA) has excellent capacitive performance and good electrical conductivity. The UV–Vis and FTIR spectra further validate that the Poly(3-APBA) is indeed obtained in pure room temperature ionic liquids [BMIM]PF6 without F− or exogenous protons. Furthermore, the Poly(3-APBA) can be used as a sensor to glucose. This paper presents an innovative and simple strategy for 3-APBA electropolymerization.

Novel asymmetric 1,3-di(alkyloxy)imidazolium based ionic liquids for liquid-phase microextraction of selected analgesics and estrogens from aqueous samples

In this study, four novel and pure room temperature ionic liquids were synthesized from basic chemicals and examined on their applicability as extraction media for liquid-phase microextraction of selected analgesics and estrogens from aqueous samples. Analyses were performed with high-performance liquid chromatography equipped with ultraviolet detection. The molecular structures of newly synthesized ionic liquids were elucidated by nuclear magnetic resonance spectroscopy. Three different extraction experiments were performed to verify their suitability as extraction media in liquid-phase microextraction. Recoveries and enrichment factors were calculated and extraction time profiles recorded to evaluate their extraction performance. Under optimized conditions high recoveries (84–92%) and acceptable enrichment factors (36–68) were obtained for the extraction of naproxen, ibuprofen, estrone and estradiol from aqueous samples. Extraction time profiles showed that equilibrium was reached after 40–80 min depending on analyte and applied ionic liquid. The proposed method was also tested on complex water samples from the nearby river (Inn) in which case same recoveries and enrichment factors were obtained. Calibration curves were linear with a coefficient of determination ranging from 0.9992 to 0.9997 for a concentration level between 2 and 20 μg mL−1. Limit of detection and limit of quantification were calculated according to DIN 32645:2008-11 for the four analytes and ranged between 0.016 and 0.060 μg mL−1 and 0.056–0.19 μg mL−1, respectively.

“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.

High Ionic Conductivity, Mechanically Strong Ion Gels for All Solid State Supercapacitor Applications

Electrochemical double layer capacitors (EDLCs) have many advantages compared with batteries and fuel cells because of their cycle life and power density. The limitation for use of EDLCs in major applications such as electric vehicles and grid storage is their low energy density. One way to increase energy density of EDLCs is to increase the stability window of the electrolytes. Room temperature ionic liquids (RTILs), which are salts with low temperature melting points, have been investigated as electrolytes in electrochemical devices, since they have useful (i.e. large) electrochemical stability windows (> 4V), are nonvolatile (and as a result often non-flammable), and are therefore safer than conventional aprotic liquid electrolytes. The utility of a EDLC device increases if it is developed in the form of a thin, solid film since it avoids leakage problems and the use of casings that decrease energy density. One method to make these films is to form iongels, which are ion conducting liquids (such as RTILs) immobilized in a polymer matrix, forming a solid polymer electrolyte (SPE). Since RTILs are typically more viscous (30-200 cP vs ~ 1 cP) than conventional aprotic or aqueous solvents, and therefore less conductive (0.1 to 18 mS/cm), it becomes important to decrease the amount of polymer required to solidify the iongel. Immobilization of the RTIL can be achieved using gelators that participate in chemical crosslinking reactions or form physical crosslinks. Gelators further increase viscosity and decrease conductivity of RTIL, which decreases the conductivity and increases the equivalent series resistance (ESR) in EDLCs. Therefore, the requirements of iongels in EDLC applications are minimum wt% of gelator, low ESR, good chemical and electrochemical stability with the electrodes and good mechanical properties (to prevent shorting the electrodes under pressure). In our previous work, we have shown that renewable, environmentally friendly, abundant and inexpensive natural polymers such as methyl cellulose (MC), (as gel former), when combined with an ionic liquid, form tough, temperature stable ion gels1,2. In this work, we developed an iongel with 5% MC as gelator and 95% 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide as the ionic liquid, for all solid state supercapacitor applications. The formed iongels have temperature dependent ionic conductivities only 1.5 to 1.8 times lower than the pure RTILs, high thermal stability up to 350oC, solid like behavior over a frequency range of 1 Hz to 100 Hz, at 25oC and a storage modulus of 5 MPa at 25oC, as shown in Figure 1. The iongel was incorporated into 3-D porous interconnected network of free standing porous carbon nanofibers prepared by an electrospinning technique and further chemically activated, yielding a high surface area of 2282 m2/g as shown in Figure 2.A specific capacitance of 137 F g-1 at 20 mV s-1was obtained for the cell corresponding to a specific energy density of 56 Wh/kg (based on total electrode mass) for a 3.5V window. At the same scan rate 163 F/g was obtained for liquid based cell. In this talk, the performance, stability and postmortem studies of the supercapacitor will be discussed. In summary we have developed novel iongels that have been solidified with only 5% methylcellulose as gelator, with excellent ionic conductivities (1.5 to 1.8 times lower than the RTIL) and mechanical properties (5MPa at 25oC) as electrolytes for all solid state supercapacitor applications. Figure 1: Comparison of liquid IL and gel IL; Log σ vs 1000/T (a) 2ndheating DSC thermograms (b) TGA thermograms (c) and storage and loss moduli as a function of frequency for gel IL at 25 °C (d). Figure 2 top left. SEM micrographs: a-CNFs and right; a-CNFs filled with iongel; bottom left. EIS of liquid- and solid-based cells and right; corresponding CVs Figure 1

The Influence of Water on the Alkyl Region Structure in Variable Chain Length Imidazolium-Based Ionic Liquid/Water Mixtures.

Solutions of room temperature ionic liquids (RTILs) and water were studied by observing the reorientational dynamics of the fluorescent probe perylene. Perylene is solvated in the alkyl regions of the RTILs. Its D2h symmetry made it possible to extract dynamical information on both in-plane and out-of-plane reorientation from time-resolved fluorescence anisotropy measurements. Perylene reorientation reports on its interactions with the alkyl chains. The RTILs were a series of 1-alkyl-3-methylimidazolium tetrafluoroborates (CnmimBF4, where n is the number of carbons in the alkyl chain), and the effects on perylene's dynamics were observed when varying the alkyl chain length of the cation (n = 4, 6, 8, and 10; butyl, hexyl, octyl, decyl) and varying the water content from pure RTIL to roughly three water molecules per RTIL ion pair. Time correlated single photon counting was used to measure the fluorescence anisotropy decays to determine the orientational dynamics. The friction coefficients for both the in-plane and out-of-plane reorientation were determined to eliminate the influence of changes in viscosity caused by both the addition of water and the different alkyl chain lengths. The friction coefficients provided information on the interactions of the perylene with the alkyl environment and how these interactions changed with chain length and water content. As the chain length increased, the addition of water had less of an effect on the local alkyl environment surrounding the perylene. The friction coefficients generally increased with higher water contents; the in-plane orientational motion was hindered significantly more than the out-of-plane motion. The restructuring of the alkyl regions is likely a consequence of a rearrangement of the ionic imidazolium head groups to accommodate partial solvation by water, which results in a change in the arrangement of the alkyl chains. At very high water content, BmimBF4 broke this general trend, with both in-plane and out-of-plane rotational friction decreasing above a water content of one water per ion pair. This decrease indicates a major reorganization of the overall liquid structure in high water content mixtures. In contrast to BmimBF4, the longer chain length RTILs are not infinitely miscible with water, and do not show evidence of a major reorganization before reaching saturation and phase-separating. The results suggest that phase separation in longer chain length BF4 RTILs is a consequence of their inability to undergo the reorganization of the alkyl regions necessary to accommodate high water concentrations.

A comparative study of room temperature ionic liquids and their organic solvent mixtures near charged electrodes

The structural properties of electrolytes consisting of solutions of ionic liquids in a polar solvent at charged electrode surfaces are investigated using classical atomistic simulations. The studied electrolytes consisted of tetraethylammonium tetrafluoroborate (NEt4-BF4), 1-ethyl-3-methylimidazolium tetrafluoroborate (c2mim-BF4) and 1-octyl-3-methylimidazolium tetrafluoroborate (c8mim-BF4) salts dissolved in acetonitrile solvent. We discuss the influence of electrolyte concentration, chemical structure of the ionic salt, temperature, conducting versus semiconducting nature of the electrode, electrode geometry and surface roughness on the electric double layer structure and capacitance and compare these properties with those obtained for pure room temperature ionic liquids. We show that electrolytes consisting of solutions of ions can behave quite differently from pure ionic liquid electrolytes.

Polymorphs in room-temperature ionic liquids: Hierarchical structure, confined water and pressure-induced frustration

Room-temperature ionic liquids (RTILs) can extract hidden information about water. Various types of hydrogen bonds of water are detected clearly in the liquid, glass, and crystal states. In addition to hydrogen bonding in water, balancing among charge (scalar), dipole (vector), and coordination number (topology) contribute to heterogeneous structure on the multiple scales in RTILs–water systems. The water-mediated hierarchical structure in the liquid is connected to macroscopic properties such as AC impedance, pH oscillations, density, and differential scanning calorimetry trace as a function of water concentration. Nanoscale water confinement was observed inside the RTILs, and the size and distribution of confined water were tuned by water concentration and temperature. The loosely packed confinement plays an important role in the engineering of next generation novel nanoheterogeneous materials. High-pressure crystal polymorphs were identified in pure RTILs by X-ray diffraction and Raman spectroscopy. By further compression, amorphous appeared partially in the deformed crystalline.

Real-time monitoring of room-temperature ionic liquid purity through optical diode-based sensing

Room-temperature ionic liquids (RTILs) are promising for use in many industries due to their unique properties, including wide electrochemical windows, low vapor pressures, high ionic conductivities, and chemical and thermal stability. All of these properties require high RTIL purity, and achieving this high purity is a major driver of RTIL manufacturing costs. Continuous flow processes to synthesize highly pure RTILs at a reduced cost have been developed, but due to exothermic synthesis reactions and temperature dependent reaction rates, these processes require real-time control. An ultraviolet LED based optical sensor has been designed to measure RTIL purity at millisecond sampling rates using a liquid flow cell. The sensor is demonstrated by measuring 1-methylimidazole (MIM) concentration in 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide ([EMIM][TFSI]). Sensor results are compared against spectroscopic measurements with good agreement.

Systematic refinement of Canongia Lopes-Pádua force field for pyrrolidinium-based ionic liquids.

Reliable force field (FF) is a central issue in successful prediction of physical chemical properties via computer simulations. While Canongia Lopes-Pádua (CL&P) FF provides good to excellent thermodynamics and structure of pure room-temperature ionic liquids (RTILs), it suffers from drastically and systematically underestimated ionic motion. This occurs due to neglected partial electron transfer from the anion to the cation, resulting in unphysically small simulated self-diffusion and conductivity and high shear viscosities. We report a systematic refinement of the CL&P FF for six pyrrolidinium-based RTILs (1-N-butyl-1-methylpyrrolidinium dicyanamide, triflate, bis(fluorosulfonyl)imide, bis(trifluoromethanesulfonyl)imide, tetrafluoroborate, chloride). The elaborated procedure accounts for specific cation-anion interactions in the liquid phase. Once these interactions are described effectively, experimentally determined transport properties can be reproduced with an acceptable accuracy. Together with the original CL&P parameters, our force field fosters computational investigation of ionic liquids. In addition, the reported results shed more light on the chemical nature of cation-anion binding in various families of RTILs.

Ion Transport in Electrolytes for Dye-Sensitized Solar Cells: A Combined Experimental and Theoretical Study

The ion transport properties of electrolytes based on room temperature ionic liquids (RTILs) used in dye-sensitized solar cells (DSCs) have been studied by electrochemical voltammetry experiments and molecular dynamics (MD) simulations. Fully atomistic models based on the Lennard-Jones potential with atomic point charges have been developed for imidazolium and pyrrolidinium imides (Tf2N). MD simulations with the proposed force fields reproduce accurately the density and the self-diffusion coefficient of the anion and cation of the RTIL, as well as their temperature dependence and the effect of the length of the alkyl chain. The diffusion coefficients of iodide/tri-iodide redox mediator in mixture of RTIL and acetonitrile have been studied by voltammetry and MD. Both experiment and simulation show a 2 orders of magnitude decrease of the diffusion coefficient of the redox mediator between pure acetonitrile and pure RTIL. However, the variation of the diffusion coefficient with the RTIL/acetonitrile mixing ratio shows that a small amount of acetonitrile is sufficient to induce an improvement of the ion transport properties of the electrolyte, which can be very beneficial to design efficient and stable electrolytes for DSCs.

Double-line Hammett relationship revealed through precise acidity measurement of benzenethiols in neat ionic media: a typical "ionic liquid effect"?

Equilibrium acidities (pKa) of 14 aromatic thiols in four pure room temperature ionic liquids (RTILs) were precisely determined and the corresponding acidity scales were established for the first time. Regression analyses show a distinct double-line Hammett relationship with similar slopes and excellent linearity (R(2) of 0.996-0.999) in all four ILs. This could be rationalized by a resonance enhanced effect of the IL cation to solvate the para substituent of feasible electronic structure (CSAR effect), revealing a typical and rarely seen "ionic liquid effect".

Isomer effect of propanol on liquid–liquid equilibrium in hydrophobic room-temperature ionic liquids

The cloud-point temperature determined the liquid–liquid phase equilibrium (LLE) of binary systems comprising hydrophobic room-temperature ionic liquids (RTILs) and propanol. The RTILs were 1-alkyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide, [Cxmim][TFSI] (2≤x≤10). Upper critical solution temperatures in LLE are inversely proportional to the Cxmim+ cation alkyl chain length, x. The propanol isomer effect indicates the critical alkyl chain length (xcritical=6–7). UNIQUAC model determined the interaction parameters (with crossing points at x=6). In pure RTILs, conformation stability of TFSI− by Raman spectroscopy changed between x=6 and 7, corresponding to the simulation-determined 90°-torsion angle at x=6.

Voltammetric behaviour of ferrocene in olive oils mixed with a phosphonium-based ionic liquid

In this paper the mass transport characteristics of both the room temperature ionic liquid (RTIL) trihexyl(tetradecyl)phosphonium bis(trifluoromethylsulfonyl)imide ([P14,6,6,6]+ [NTf2]−) and the RTIL mixed with an olive oil sample were investigated by voltammetry, using ferrocene as the probe molecule. The RTIL was used as electrolyte to increase the conductivity of the vegetable oil. To avoid problems related to ohmic drop, the measurements were taken with platinum microdisk electrodes, 10–12.5μm radius. Cyclic voltammetric measurements at different scan rates were performed over the range 1–200mVs−1, while the concentration of ferrocene was varied over the range 2.5–10mM. The results obtained indicated that, under these conditions, a mixed radial-planar diffusion regime applied. Diffusion coefficient values for Fc in both pure RTIL and various oil/RTIL mixtures were evaluated by using the experimental peak current against square root of scan rate plots fitted to the theoretical relationship that applies for microdisk electrodes under a mixed diffusion regime. Digital simulation was employed to support the interpretation of the experimental voltammograms and also to obtain the diffusion coefficient of Fc+ in both RTIL and oil/RTIL media. Diffusion coefficient values of Fc and Fc+ depended on the sample matrix and essentially reflected the viscosity of the investigated media. The results obtained here can be useful to model voltammetric measurements of analytes in viscous and low conducting vegetable oil matrices.

Direct Evidence of Confined Water in Room-Temperature Ionic Liquids by Complementary Use of Small-Angle X-ray and Neutron Scattering.

The direct evidence of confined water ("water pocket") inside hydrophilic room-temperature ionic liquids (RTILs) was obtained by complementary use of small-angle X-ray scattering and small-angle neutron scattering (SAXS and SANS). A large contrast in X-ray and neutron scattering cross-section of deuterons was used to distinguish the water pocket from the RTIL. In addition to nanoheterogeneity of pure RTILs, the water pocket formed in the water-rich region. Both water concentration and temperature dependence of the peaks in SANS profiles confirmed the existence of the hidden water pocket. The size of the water pocket was estimated to be ∼3 nm, and D2O aggregations were well-simulated on the basis of the observed SANS data.

Fluorescence correlation spectroscopy study on room-temperature ionic liquids

Unique fluorescence behavior was reported in room-temperature ionic liquids having imidazolium cations. Due to the molecular electronic energy level of the imidazolium cation, fluorescence in the visible range from pure ionic liquids is not expected, but was readily observed. Fluorescence correlation spectroscopy (FCS) was used to find the nature of this unique fluorescence by investigating the fluorescence fluctuation and the number density of fluorophores. FCS signal was observed in pure room-temperature ionic liquids having different cations and anions, which is considered to come from the molecular aggregate of room-temperature ionic liquid. The size and the number density of aggregates in pure ionic liquids were measured by using FCS.

Molecular Dynamics Simulation Study of the Capacitive Performance of a Binary Mixture of Ionic Liquids near an Onion-like Carbon Electrode.

An equimolar mixture of 1-methyl-1-propylpyrrolidinium bis(trifluoromethylsulfonyl)imide ([C3mpy][Tf2N]), 1-methyl-1-butylpiperidinium bis(trifluoromethylsulfonyl)imide ([C4mpip][Tf2N]) was investigated by classic molecular dynamics (MD) simulation. Differential scanning calorimetry (DSC) measurements verified that the binary mixture exhibited lower glass transition temperature than either of the pure room-temperature ionic liquids (RTILs). Moreover, the binary mixture gave rise to higher conductivity than the neat RTILs at lower temperature range. In order to study its capacitive performance in supercapacitors, simulations were performed of the mixture, and the neat RTILs used as electrolytes near an onion-like carbon (OLC) electrode at varying temperatures. The differential capacitance exhibited independence of the electrical potential applied for three electrolytes, which is in agreement with previous work on OLC electrodes in a different RTILs. Positive temperature dependence of the differential capacitance was observed, and it was dominated by the electrical double layer (EDL) thickness, which is for the first time substantiated in MD simulation.

Thermophysical and spectroscopic studies of room temperature ionic liquid, 1-butyl-3-methylimidazolium hexafluorophosphate in Tritons

The thermophysical properties viz. density ρ, speed of sound u, and specific conductivity κ of pure room temperature ionic liquid (1-butyl-3-methylimidazolium hexafluorophosphate) and its binary formulations with Triton X-45 and Triton X-100 have been studied over the entire composition range at different temperatures (293.15 to 323.15)K. Excess molar volume VE, deviation in isentropic compressibility ΔKS, partial molar excess volume ViE, deviation in partial molar isentropic compressibility ΔKS,i, deviation in specific conductivity Δκ have also been estimated and analysed. Spectroscopic properties (IR, 1H and 13C NMR) of these mixtures have been investigated in order to understand the structural and interactional behaviour of formulations studied. The magnitude of interactions between the two components increases with addition of number of oxyethylene groups in Tritons and with rise in temperature. Spectroscopic measurements indicate that interactions are mainly taking place through the five member ring of room temperature ionic liquid and six member ring of Tritons.