Quaternary Ammonium-based Ionic Liquids Research Articles

Electrochemical stability of low viscosity ion-pair electrolytes: Structure and interaction in quaternary ammonium-based Ionic liquid containing bis(trifluoromethylsulfonyl)imide anion and analogue

Quaternary ammonium-based ionic liquids (QAIL) consist of an aliphatic cation and possess characteristic properties different from those of aromatic (like imidazolium) with extensive cited applications. The redox stability of QA cations has attractively nominated them to achieve static and dynamic electrochemical phenomena. Herein, we investigated the influence of various anions (bis(fluorosulfonyl)imide [FSI]− and bis(trifluoromethylsulfonyl)imide [NTf2]−) on the structure, electronic, and electrochemical properties of low-viscosity ILs comprising QA cation (triethylpentyl ammonium [N2225]+) by employing highly versatile empirical exchange-correlation functional M06–2X in the context of density functional theory (DFT). The electronic structure, cation-anion interaction energy, dipole moment, cation-anion charge transfer, cathodic and anodic potential boundaries, electrochemical window (ECW), and density of state (DOS) were calculated and discussed. Liquid state studied by polarizable continuum model (PCM). The thermodynamics cycle method, an alternative to HOMO/LUMO method, was used to predict ECW's more realistic. ECWs for [N2225][FSI] ≥ [N2225][NTf2] were found to be wider than the experimental imidazolium counterpart by about two volts. [FSI]− anion is overwhelmingly involved in charge transfer with the cation compared to [NTf2]−. The more redox-stable [N2225][FSI] IL is expected to have less corrosive effects with metal electrodes because the anion (1) cis conformer takes a particular orientation relative to the cation, (2) has a higher charge transfer, and (3) F's atoms have a higher occupation number than [N2225][NTf2] IL. Therefore, these results provide insight for further investigation to expand the electrochemical application of redox-stable aliphatic QAILs involving the two targeted anions.

Highly selective extraction of scandium(III) from rare earth elements using quaternary ammonium based ionic liquids: Experimental and DFT studies

Global demand for rare earth elements (REEs) is steadily increasing, emphasizing the necessity of effective extraction and recovery methods. Although REEs recovery from electronic waste using ionic liquid (IL) extractants offers an alternative solution to avoid potential adverse environmental impacts during traditional mining and processing, highly efficient and selective extraction is still essential. Especially, due to similarities with other REEs, recovery of scandium (Sc(III)) is confronting grand challenges. Herein, quaternary ammonium based ILs (QA-ILs), i.e., [N333 MeOAc][Tf2N] and [N444 MeOAc][Tf2N], have been successfully synthesized for selective Sc(III) extraction from other REEs under various conditions, e.g., initial acidity and IL concentration. Both ILs demonstrate superior selectivity for Sc(III) extraction from other REEs. Specifically, at pH 4.5 and 5, the extraction efficiency of Sc(III) using [N333 MeOAc][Tf2N] was 73.6 % and 83.4 %, respectively, while it was high up to 90.5 % and 95.9 %, respectively, using [N444 MeOAc][Tf2N]. Because of stronger hydrophobicity, [N444 MeOAc][Tf2N] exhibited a higher extraction efficiency. Furthermore, [N444 MeOAc][Tf2N] demonstrated a higher selectivity for Sc(III) as compared to other REEs, with high separation factor of 17 for Sc(III)/Lu(III) and Sc(III)/Yb(III). Additionally, the ILs can be recycled with a high stripping efficiency up to 86 % using 4 mol·L−1 H2SO4 solution. Density functional theory calculations further validated neutral exchange of Sc(III) in the neutral IL extraction process. This study presents a feasible solvent extraction system using novel QA-ILs for highly effective and selective Sc(III) extraction from waste streams.

Interface Engineering with Quaternary Ammonium-Based Ionic Liquids toward Efficient Blue Perovskite Light-Emitting Diodes.

Perovskite light-emitting diodes (PeLEDs) have become a hot research topic in recent years and can now achieve an external quantum efficiency (EQE) of over 22% for green and red devices. However, the efficiency of blue PeLEDs, which are essential for display applications, lags far behind their green and red counterparts. The interface of the PeLEDs has a critical influence on the carrier transport and exciton recombination dynamics, and interface engineering is considered to be an effective strategy to improve the device performance. Herein, quaternary ammonium-based ionic liquids serve as an interfacial modification layer to significantly improve the device efficiency and stability. The interaction of quaternary ammonium cations with Pb(Br/Cl)6 octahedra promotes nucleation sites, which significantly improves the morphology of perovskite films and reduces the formation of defects in films. In addition, ion migration is also effectively suppressed in the device. As a result, with tributylmethylammonium bromide (TMAB) used as the interface layer, the EQE of the device is successfully increased from 3.5 to 6.7%, and the operational stability with a half-lifetime (T50) is increased by over 12 times. Our work provides a new class of interface modification materials toward high-performance blue PeLEDs.

Insights into quaternary ammonium-based ionic liquids series with tetrafluoroborate anion for CO2 capture

In this paper, the structures of quaternary ammonium ionic liquids (QAILs) composed of tetrafluoroborate anion and quaternary ammonium cations with different alkyl chains and their interactions with CO2 molecule were studied by density functional theory at the B3LYP-D3/6–311++G(d, p) level of theory. Geometries of isolate cations/anion, ionic pairs and QAILs-CO2 systems have been fully optimized. QTAIM and NCI analyses have also been performed to obtain the interaction information of fragments for QAILs-CO2 systems. NCI analysis also demonstrates that [BF4]− anion and quaternary ammonium cations actually have the synergistic effects in the CO2 capture process by QAILs. GKS-EDA method was firstly applied for incisive understanding of QAILs-CO2 systems from energetic perspectives; Moreover, we also took advantage of COSMO-RS calculation to obtain CO2 macroscopic solubility in QAILs, which is in good correspondence with the GKS-EDA results. Additionally, gas selectivity results calculated using COSMO-RS theory indicate that the selectivities of CO2/CO and CO2/CH4 decrease gradually as alkyl side chains of QAILs elongate in contrast to the increase of CO2/H2 selectivity. At last, molecular dynamics simulation was also conducted to obtain the dynamic transport property of CO2 in QAILs.

Simulations of Double Layer Structure and Differential Capacitance of Quaternary Ammonium-Based Ionic Liquids: Effect of Switching the Length of Alkyl Chains

Quaternary ammonium-based ionic liquids (QaILs) have non-flammability, non-volatility, and thermal/chemical/electrochemical stabilities and are expected to be electrochemically applied. QaILs are superior to well-known imidazolium-based ILs in the wide potential window and high cationic designability. While the number of studies focusing on QaILs is limited,[1] further knowledge is needed to utilize the characteristics of QaILs. In this study, we performed molecular dynamics simulations at the interface between QaILs and the graphene electrode. The QaILs are composed of a common anion, bis(trifluoromethanesulfonyl)amide (TFSA−) and different cations: butyltrimethylammonium (N1114 +) dibutyldimethylammonium (N1144 +), tributylmethylammonium (N1444 +), tetrabutylammonium (N4444 +). By substituting methyl and butyl groups in Qa cations, we investigated how the number of long alkyl chains affects the potential dependence of differential capacitance and the electric double layer structure.[2] The Qa cations have major two orientations on the electrode: lying orientation where all the butyl chains are parallel to the electrode (Figure a) and standing orientation where one or more butyl chains are pointing to the ILs bulk (Figure b). N4444+ only shows standing orientation because of its geometric restriction. Compositions of the first interfacial layer reflect both the cationic orientation and surface charge density. As the electrode is negatively charged up, the compositions indicate the increase in the number of cations and different behavior of butyl chains depending on the Qa cations. Orientation analysis of the butyl chain indicates that the increase in lying orientation occurs at moderately negative (< ~−2 V) potentials, and the increase in standing orientation occurs at further negative potentials.As the potential deceases, the differential capacitance of all the QaILs drastically decreases in the potential range from 0 to ~−2V and gradually decreases at more negative potentials (Figure c). In the latter potential range, the differential capacitances show an upward discrepancy from predicted curves from Kornyshev model.[3][4] The discrepancy begins at the potentials where the standing orientation starts to increase, which implies a correlation between the differential capacitance and the cationic orientation. The discrepancy is greater for QaILs composed of cations with fewer butyl chains. The orientation effect is significant for such cations because those in lying and standing orientation have a great difference in occupation space in the first ionic layer.

Unraveling the Mechanism of Enhanced Lithium Salt Solubility in Water-in-Salt Electrolytes Containing Ionic Liquids

The narrow electrochemical stability window of aqueous electrolytes of ~1.5 V can be extended to >2.5 V employing high salt concentration.1-3 At a molality of, e.g., 21 moles of lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) per kilogram of water, the water:lithium ratio equals 2.65, causing strong cation-water interactions and the alignment of TFSI anions in a water-blocking electrochemical double-layer at the cathode, resulting in particularly high oxidative stability.1,2 As these electrolytes are typically saturated solutions at room temperature, they tend to crystallize below room temperature. We recently showed that employing salts with asymmetric anions such as lithium (pentafluoroethanesulfonyl)(trifluoromethanesulfonyl)imide (LiPTFSI) is a very effective strategy to suppress crystallization in such water-in-salt electrolytes to temperatures below −10 °C.4,5 LiPTFSI has further been combined with LiTFSI to form a solution with an overall molality of 56 mol kg−1, lowering the water:lithium ratio to 1.6 Reducing the water:lithium ratio is a key challenge to enhance the reductive stability of water-in-salt electrolytes. However, increasing the salt concentration to such high levels leads to a low ionic conductivity of only 0.1 mS cm−1 at 30 °C.6 Recently it was demonstrated that the addition of quaternary ammonium-based ionic liquids to a water-in-salt electrolyte increases LiTFSI solubility, while maintaining high ionic conductivity.7 Yet it is unclear, where the enhanced LiTFSI solubility originates from.In this contribution, we unravel the mechanism enabling very high lithium salt solubility in the presence of ionic liquids in water-in-salt electrolytes via nuclear magnetic resonance and vibrational spectroscopy.8 We investigate hybrid electrolytes with a water:lithium ratio of only 0.93 and a LiTFSI molality of up to 60 mol kg−1, almost three times as high as in water. Generally, these ternary water-ionic liquid-lithium salt electrolytes have much better transport properties at high salt concentration reaching 1.4 mS cm−1 at 25 °C at a molality of 40 mol kg−1 LiTFSI and 20 mol kg−1 ionic liquid. In addition, the enhanced reductive stability enables stable cycling of a Li4Ti5O12 anode in combination with a nickel-rich lithium nickel manganese cobalt oxide (NMC811) cathode with high Coulombic efficiency demonstrating the promising potential of water-in-salt electrolytes.

Simulating the Effect of Anions on Spreading of Nanodroplets and the Monolayer Behavior of Quaternary Ammonium-Based Ionic Liquids on Li(100) and Li(110) Metal Facets

Choice of ionic liquids (ILs) with 〖[NTf_2]〗^- versus [FSI]ˉ (stability promoting and fluidity promoting, respectively) anions has recently attracted attention in different applications for issues ...

Effect of Switching the Length of Alkyl Chains on Electric Double Layer Structure and Differential Capacitance at the Electrode Interface of Quaternary Ammonium-Based Ionic Liquids Studied Using Molecular Dynamics Simulation

Electric double layer structure at the electrode interface has been studied by using molecular dynamics simulation on four quaternary ammonium-based ionic liquids (QaILs) to investigate the effect ...

Synthesis of Quaternary Ammonium Room-Temperature Ionic Liquids and their Application in the Dissolution of Cellulose

In this work, several kinds of quaternary ammonium-based room-temperature ionic liquids (QA RTILs) are synthesized by alkylation and ion-exchange reactions for the rapid dissolution of cellulose. The applications of cellulose materials have been limited due to their poor solubility in conventional organic solvents, because of a high degree of structural regularity and a large number of hydrogen bonds. The prepared ionic liquids were identified by nuclear magnetic resonance, elemental analysis, and liquid chromatography-mass spectrometry. The results indicated that N,N,N-triethylhexan-1-aminium acetate (N6222OAc), tetrahexylammonium acetate (N6666OAc), and N,N,N,N′,N′,N′-hexaethyldecane-1,10-diaminium acetate (C10(N222OAc)2) exhibited good cellulose-dissolution without any pretreatment. The regenerated cellulose films with a low degree of crystallization of the cellulose II phase were also prepared easily in this process using N6222OAc due to its polar and small cation. These QA RTILs can be used as non-derivatizing solvents for cellulose and can also be easily recycled because of their thermostable and nonvolatile properties.

Surface Structure of Quaternary Ammonium-Based Ionic Liquids Studied Using Molecular Dynamics Simulation: Effect of Switching the Length of Alkyl Chains

The surface structure of four quaternary ammonium-based ionic liquids (QaILs) at the QaIL|vacuum interface has been analyzed using molecular dynamics simulation to investigate the effect of switchi...

Measurements of activity coefficients at infinite dilution for organic solutes in two quaternary ammonium-based ionic liquids [DDA][ClO4] and [DDA][BF4

The paper presents new data on the activity coefficient at infinite dilution (γ13∞) for 29 various organic solutes: alkanes, alkenes, al-kynes, cycloalkanes, alcohols, ethers, ketones and aromatic hydrocarbons in two quaternary-ammonium based ionic liquids (quat-based ILs): didecyldimethylammonium perchlorate [DDA][ClO4] and didecyldimethylammonium tetrafluoroborate [DDA][BF4]. The activity coefficient at infinite dilution and physicochemical properties of two mentioned ionic liquids, were determined by inverse gas chromatography at four different temperatures: 308K, 323K, 338K and 353K. Additionally, on the basis of the specific retention volume (Vg0) the Flory – Huggins interaction parameters (χ∞) were determined. In order to identify the fundamental interaction between solute and solvent inside the column, the partial molar excess enthalpies at infinite dilution (ΔH1E,∞) were calculated on the basis of experimental γ13∞ values. The selectivity (Sij∞) and capacity (kj∞) at infinite dilution for a few different separation problems: hexane/benzene, cyclohexane/benzene and hexane/tetrahydrofuran were calculated from the experimental γ13∞ values to evaluate the possible use of the ionic liquids studied as a new class of solvents in liquid-liquid extraction and in other extraction or microextraction methods. The values of the above-mentioned parameters were compared and discussed taking into regard the chemical structures of both quaternary ammonium-based ionic liquids, including the same cation and their interactions with the organic solute.

A Novel Method for Prediction of Impact Sensitivity of Quaternary Ammonium-based Eenergetic Ionic Liquids

A Novel Method for Prediction of Impact Sensitivity of Quaternary Ammonium-based Eenergetic Ionic Liquids

Solvent effect on the fixation of CO2 catalyzed by quaternary ammonium-based ionic liquids bearing different numbers of hydroxyl groups: A combined molecular dynamics simulation and ONIOM study

The solvent effect of ionic liquids on CO2 fixation catalyzed by hydroxyl-functionalized quaternary ammonium-based ionic liquids is thoroughly investigated by ONIOM method associated with the molecular dynamics simulation. As compared with the catalytic activity determined in experiment, the catalytic activity estimated by ONIOM model is more credible than previous result calculated by the polarized continuum model. The critical hydrogen bond and C-Br interaction are analyzed by non-covalent interaction and the atoms in molecules methods. The analysis indicates that the electrophilic activation aroused by hydrogen bond provides more contribution than nucleophilic activation aroused by C-Br interaction in reaction catalyzed by trihydroxyethylethyl ammonium bromide. In contrast, the nucleophilic activation is more important in reactions catalyzed by other three ionic liquids. Choice of the suitable model is possible to obtain the reliable catalytic activity, which would be comparable with the experimental result.

Interfacial Structure at the Quaternary Ammonium-Based Ionic Liquids|Gold Electrode Interface Probed by Surface-Enhanced Infrared Absorption Spectroscopy: Anion Dependence of the Cationic Behavior

The interfacial structure at the quaternary ammonium-based ionic liquids(ILs)|gold(Au) electrode interface has been studied using surface-enhanced infrared absorption spectroscopy (SEIRAS). Four anions, bis(perfluoroalkanesulfonyl)amide (CnCnN–; n = 0, 1, 2, 4), have been combined with a quaternary ammonium cation, trioctylmethylammonium (N8881+), to investigate the influence of the perfluoroalkyl chain length of the anion on the behavior of the quaternary ammonium cation at the interface. In addition, to investigate the effect of the alkyl chain length of the quaternary ammonium cations on the cationic behavior, we have also combined a cation with a shorter alkyl chain, tributylmethylammonium (N4441+) with C1C1N–. Thus, we have performed SEIRAS measurements at the Au interface of five ILs: [N8881+][CnCnN–] (n = 0, 1, 2, 4) and [N4441+][C1C1N–]. The four CH stretching bands originating from the quaternary ammonium cations have been individually analyzed, enabling us to reveal the behavior of the quaternar...

Theoretical studies on CO2 capture behavior of quaternary ammonium-based polymeric ionic liquids.

Quaternary ammonium-based polymeric ionic liquids (PILs) are novel CO2 sorbents as they have high capacity, high stability and high binding energy. Moreover, the binding energy of ionic pairs to CO2 is tunable by changing the hydration state so that the sorbent can be regenerated through humidity adjustment. In this study, theoretical calculations were conducted to reveal the mechanism of the humidity swing CO2 adsorption, based on model compounds of quaternary ammonium cation and carbonate anions. The electrostatic potential map demonstrates the anion, rather than the cation, is chemically preferential for CO2 adsorption. Further, the proton transfer process from water to carbonate at the sorbent interface is successfully depicted with an intermediate which has a higher energy state. By determining the CO2 adsorption energy and activation energy at different hydration states, it is discovered that water could promote CO2 adsorption by reducing the energy barrier of proton transfer. The adsorption/desorption equilibrium would shift to desorption by adding water, which constitutes the theoretical basis for humidity swing. By analyzing the hydrogen bonding and structure of the water molecules, it is interesting to find that the CO2 adsorption weakens the hydrophilicity of the sorbent and results in release of water. The requirement of latent heat for the phase change of water could significantly reduce the heat of adsorption. The special "self-cooling" effect during gas adsorption can lower the temperature of the sorbent and benefit the adsorption isotherms.

Quaternary ammonium-based ionic liquids bearing different numbers of hydroxyl groups as highly efficient catalysts for the fixation of CO2: a theoretical study by QM and MD

The mechanism of coupling reactions of CO2 with PO catalyzed by NEtn(HE)4−nBr (n = 1–4) by QM and MM.

Quaternary Ammonium-Based Room Temperature Ionic Liquids as Components of Carbonate Electrolytes for Li-ion Batteries: Electrochemical Performance and Thermal Properties

Quaternary Ammonium-Based Room Temperature Ionic Liquids as Components of Carbonate Electrolytes for Li-ion Batteries: Electrochemical Performance and Thermal Properties

Quaternary Ammonium-Based Room Temperature Ionic Liquids as Components of Carbonate Electrolytes for Li-ion Batteries: Electrochemical Performance and Thermal Properties

Quaternary Ammonium-Based Room Temperature Ionic Liquids as Components of Carbonate Electrolytes for Li-ion Batteries: Electrochemical Performance and Thermal Properties

The effect of quaternary ammonium-based ionic liquids on copper electrodeposition from acidic sulfate electrolyte

The effect of quaternary ammonium-based ionic liquids (ILs) including tetraethylammonium hydrogen sulfate (NEt4HSO4) and tetrabutylammonium hydrogen sulfate (NBu4HSO4) on copper electrodeposition from acidic sulfate electrolyte was investigated by cyclic voltammetry and chronoamperometric measurements. These ILs were found to have a blocking effect on the copper electroreduction and induced the formation of more leveled and fine-grained cathodic deposits. Analysis of the dimensionless current–time transients indicated that the electrodeposition of copper was involved with instantaneous three-dimensional nucleation with diffusion-controlled growth. The addition of ILs induced the instantaneous nucleation to more progressive one. Data obtained from X-ray diffraction spectra revealed that the presence of these ILs strongly affected the crystallographic orientation of the electrodeposited copper with a (220) preferential orientation.

Prediction of Density, Surface Tension, and Viscosity of Quaternary Ammonium-Based Ionic Liquids ([N222(n)]Tf2N) by Means of Artificial Intelligence Techniques

In this work, thermophysical properties of quaternary ammonium-based ionic liquids (ILs) including density, surface tension, and viscosity are produced by two powerful artificial intelligence techniques: genetic function approximation (GFA) and artificial neural network (ANN). In proposed GFA and ANN models, the critical temperature and water content of studied ILs ([N222(n)]Tf2N with n = 5, 6, 8, 10, and 12) as well as operation temperature were given as the input parameters and the density, surface tension, and viscosity were predicted as the output results. The obtained results reveal that the selected input parameters are appropriate for prediction of thermophysical properties of quaternary ammonium-based ILs. In addition, the high statistical quality represented by various criteria and the low prediction errors of the presented models indicate that they can accurately predict the density, surface tension, and viscosity of new ILs without recourse to experimental data.