Ionic Liquid Concentration Research Articles

Recovery of ionic liquids from aqueous solutions using membrane technology

Ionic liquids (ILs) have great potential as solvents and catalysts in the most diverse areas of the chemical industry. However, the need for a process that allows the recycling and purification of ILs in an efficient and economically viable manner is restricting the practical application of these solvents. The recycling processes most used to recover ILs are distillation and evaporation, followed by extraction and crystallization. However, most of these processes demand high energy consumption, or temperatures that may compromise the structural and chemical stability of the ILs. This work focuses on understanding the separation of ionic liquid from aqueous solution using membranes, a technique widely used in industry. The separation of eleven ILs (([C4mim][AOc], [C4mim][SCN], [C4mim][CF3SO3], [C4mim][CF3CO2], [C4mim][Cl], [C8mim][Cl], [P4444][Cl], [N4444][Cl], [C4mpip][Cl], [C4mpyr][Cl] and [C4-2-mpy][Cl]) was studied using a nanofiltration (NF270) and a reverse osmosis (BW30LE) membrane. The influence of cation and anion, pressure, IL concentration, and temperature, on the separation of ILs, was evaluated. The Donnan exclusion mechanism was found to be the limiting factor for the reverse osmosis, while the combination of concentration polarization and sieving mechanism was the limiting factor for nanofiltration membrane. The increase of temperature and pressure leads to an increase in the volumetric flux at the cost of a decrease of the IL retention. On the other hand, the increase in the concentration of the IL solution resulted in an increase in the osmotic pressure and, consequently, a decrease in the volumetric flow and a decrease in the rejection of the IL.

Modulation of Insulin Amyloid Fibrillization in Imidazolium-Based Ionic Liquids with Hofmeister Series Anions.

Amyloid fibrils have immense potential to become the basis of modern biomaterials. The formation of amyloid fibrils in vitro strongly depends on the solvent properties. Ionic liquids (ILs), alternative solvents with tunable properties, have been shown to modulate amyloid fibrillization. In this work, we studied the impact of five ILs with 1-ethyl-3-methylimidazolium cation [EMIM+] and anions of Hofmeisterseries hydrogen sulfate [HSO4-], acetate [AC-], chloride [Cl-], nitrate [NO3-], and tetrafluoroborate [BF4-] on the kinetics of insulin fibrillization and morphology, and the structure of insulin fibrils when applying fluorescence spectroscopy, AFM and ATR-FTIR spectroscopy. We found that the studied ILs were able to speed up the fibrillization process in an anion- and IL-concentration-dependent manner. At an IL concentration of 100 mM, the efficiency of the anions at promoting insulin amyloid fibrillization followed the reverse Hofmeister series, indicating the direct binding of ions with the protein surface. At a concentration of 25 mM, fibrils with different morphologies were formed, yet with similar secondary structure content. Moreover, no correlation with the Hofmeister ranking was detected for kinetics parameters. IL with the kosmotropic strongly hydrated [HSO4-] anion induced the formation of large amyloid fibril clusters, while the other kosmotropic anion [AC-] along with [Cl-] led to the formation of fibrils with similar needle-like morphologies to those formed in the IL-free solvent. The presence of the ILs with the chaotropic anions [NO3-] and [BF4-] resulted in longer laterally associated fibrils. The effect of the selected ILs was driven by a sensitive balance and interplay between specific protein-ion and ion-water interactions and non-specific long-range electrostatic shielding.

TiO2 nanostructures synthesized by electrochemical anodization in green protic ionic liquids for photoelectrochemical applications

This work studies the influence of the 2-hydroxyethylammonium acetate (2-HEAA) ionic liquid (IL) as an electrolyte in the electrochemical anodization of titanium for the synthesis of nanostructures for photoelectrochemical water splitting. Different 2-HEAA IL concentrations were used ranging from 0 to 4% v/v (IL-0 to IL-4) in electrolytes containing NH4F, water and ethylene glycol. Morphological, structural and electrochemical characterization of the nanostructures was carried out by means of field emission scanning electron microscopy (FE-SEM), high resolution transmission electron microscopy (HRTEM), X-ray diffraction (XRD), electrochemical impedance spectroscopy (EIS), and Mott-Schottky (MS) analysis. Additionally, photoelectrochemical tests were carried out in order to evaluate the efficiency of these materials as catalysts for water splitting applications. According to the obtained results, the electrolyte used for electrochemical anodization should contain little amount of NH4F (0.05 M) in order to obtain efficient nanostructures for photoelectrochemical purposes. However, small concentrations of IL (IL-0.25) resulted in nanostructures with higher photocurrents than doubling the NH4F concentration to 0.1 M. Therefore, the IL addition contributes to a more sustainable electrolyte formulation. The best photoelectrochemical response for water splitting processes was obtained for the nanostructures anodized with 1% v/v of 2-HEAA IL (IL-1) due to their high surface/area (higher pore diameters, smaller nanotubes wall thickness and higher nanotubes lengths), better crystallinity and electrochemical response, showing photocurrents more than 100% higher than the ones obtained for the nanotubes anodized without IL.

Experimental investigation of ionic liquid as an additive in enhancing the rheological and filtration properties of water-based drilling fluid

The design of the drilling fluid is unquestionably important for the overall optimization of the drilling operation. The type of components utilized for the drilling fluid construction, as well as their proportions, contribute to the necessary rheological and filtration loss attributes. The objective of this study is to determine how the properties of the water-based drilling fluid are affected by addition of specific concentrations of ionic liquid (1-Butyl-3-Methylimidazolium-Chloride). Ionic liquids have a favorable effect on the rheology of the drilling fluid while diminishing the filtrate loss values, in addition to limiting clay swelling at particular concentrations. At 0.4% of IL the filtration loss was observed to be the least.

Mass Transfer Characteristics of CO2 and Blended Aqueous Solutions of [C2OHmim][Lys]/MDEA in a Microchannel

In this paper, the two-phase flow and mass transfer process of CO2 and [C2OHmim][Lys]/MDEA mixed aqueous solution in a T-shaped microchannel were investigated systematically. By using a high-speed camera connected to a computer, the two-phase flow patterns were recorded online, including the Taylor flow and a small amount of Taylor-bubbly flow. And the effects of ionic liquid concentration and two-phase flow ratio (QG/QL) on bubble length, specific surface area, gas holdup, and mass transfer coefficient were studied experimentally. The results indicate that the blended solution of [C2OHmim][Lys]/MDEA could significantly enhance two-phase mass transfer compared to single N-methyldiethanolamine aqueous solution. The reaction mechanism between CO2 and ionic liquid/amine mixed aqueous solution was also analyzed. On the basis of experimental data, some new correlations for predicting the bubble initial length and the volumetric mass transfer coefficient were proposed, which matched well with the experimental data. This work is helpful to provide new ideas for the design of CO2 absorbents and further improve the data of gas–liquid mass transfer in microchannels.

Small angle X-ray scattering investigation of ionic liquid effect on the aggregation behavior of globular proteins

Globular proteins are well-folded model proteins, where ions can substantially influence their structure and aggregation. Ionic liquids (ILs) are salts in the liquid state with versatile ion combinations. Understanding the IL effect on protein behavior remains a major challenge. Here, we employed small angle X-ray scattering to investigate the effect of aqueous ILs on the structure and aggregation of globular proteins, namely, hen egg white lysozyme (Lys), human lysozyme (HLys), myoglobin (Mb), β-lactoglobulin (βLg), trypsin (Tryp) and superfolder green fluorescent protein (sfGFP). The ILs contain ammonium-based cations paired with the mesylate, acetate or nitrate anion. Results showed that only Lys was monomeric, whereas the other proteins formed small or large aggregates in buffer. Solutions with over 17 mol% IL resulted in significant changes in the protein structure and aggregation. The Lys structure was expanded at 1 mol% but compact at 17 mol% with structural changes in loop regions. HLys formed small aggregates, with the IL effect similar to Lys. Mb and βLg mostly had distinct monomer and dimer distributions depending on IL type and IL concentration. Complex aggregation was noted for Tryp and sfGFP. While the anion had the largest ion effect, changing the cation also induced the structural expansion and protein aggregation.

Highly stretchable, repeatable, and easy-to-prepare ionogel based on polyvinyl chloride for wearable strain sensors

Conventional hydrogels are prone to water loss and instability, while non-hydrogel materials can be designed with high stability and repeatability. Therefore, a flexible sensing material was developed to meet the requirements of high elasticity, good stability, and high repeatability using a simple physical blending method. The developed ionogel comprised polyvinyl chloride (PVC) gel as the elastomer matrix, ionic liquid (IL) 1-ethyl-3-methylimidazolium thiocyanate as the dielectric, and dibutyl adipate (DBA) as the plasticizer. The PVC organic-ionogel exhibited good physicochemical stability without any phase change in the range of − 30 to 127 °C, and it had a maximum tensile strain of 424 %. Its shape and dimensions remained unchanged in air for 60 days, and the sensing performance was maintained following exposure to air for over a year. Moreover, the PVC organic-ionogel with moderate DBA and IL contents (DBA 7, IL 3 %) showed the best performance, which exhibited the best linearity with a relative error of only 0.96 %, sensitivity of 1.90, modulus of 17.71 kPa, response time of 161 ms, and continuous and stable operation for 35,000 cycles. This excellent performance enabled the PVC organic-ionogel to detect a range of human movements, namely finger flexion, throat vibration, muscle contraction, daily movements, and special limb movements, such as Tai Chi, with high accuracy and sensitivity. This work provides a new approach for the design of flexible sensing materials with variable parameters, in addition to a new solution for the development of wearable devices, sports-related risk monitoring, and boxing action optimization.

High-Performance Sustainable Electrochromic Devices Based on Carrageenan Solid Polymer Electrolytes with Ionic Liquid.

The development of sustainable functional materials with strong potential to be applied in different areas has been growing and gaining increasing interest to address the environmental impact of current materials and technologies. In this scope, this work reports on sustainable functional materials with electrochromic properties, based on their increasing interest for a variety of applications, including sensing technologies. The materials have been developed based on a natural derived polymer, carrageenan, in which different amounts of the ionic liquid (IL) 1-ethyl-3-methylimidazolium thiocyanate ([EMIM][SCN]) were blended. It is shown that the addition of different amounts of IL to the carrageenan matrix does not affect the properties of the samples in terms of morphology or physicochemical and thermal properties, the most significant difference being the increase of the ionic conductivity with increasing IL content, ranging from 2.3 × 10-11 S·cm-1 for pristine carrageenan to 4.6 × 10-4 S·cm-1 for the samples with 5 and 60 wt % IL content, respectively. A electrochromic device has been developed based on the different IL/carrageenan samples as electrolyte and poly(3,4-ethylenedioxythiophene) polystyrenesulfonate (PEDOT:PSS) as electrodes. Spectroelectrochemistry testing demonstrates functional devices at low voltages between 0.3 and -0.9 V. Among the different samples, the one with 15 wt % IL content presents the best conditions for application, presenting an oxidation time of 6 s, a reduction time of 8 s, and a charge density of 1150 and 1050 μC·cm-2 for oxidation and reduction, respectively. The same sample also presents excellent optical density as a function of load density, presenting an optical switch (Δ%Tx) of 99%. Thus, it is demonstrated that it is possible to develop high efficiency and sustainable electrochromic devices based on natural polymers and ionic liquids.

Conformation features and interaction of pyrrolidinium-based ionic liquids immobilized with silicon dioxide: Infrared spectroscopy

Ionic liquids (ILs) based on pyrrolidinium cation, 1-butyl-1-methylpyrrolidinium bis(trifluoromethylsulfonyl)imide (BMPyrrTFSI) and 1-butyl-1-methylpirrolidinium dicyanamide (BMPyrrN(CN)2), were incorporated into the silica matrix (SiO2, particle size about 80 nm) by a simple mixing procedure. Semitransparent phase-stable ionogels with an IL content of more than 90 wt% have been obtained and studied by FTIR spectroscopy. The analysis of microscopic mechanisms of interaction, in particular, hydrogen bonding, was carried out using the procedure of fitting the characteristic bands of pure and confined ILs. The observed changes in the position and intensity of some characteristic frequencies were interpreted in terms of the interaction of SiO2 with IL. Under confined condition, the cis–trans equilibrium of both the TFSI− anion and BMPyrr+ cation changes in favor of the trans population due to the predominant interaction of cis conformers with silica walls. This data for confined BMPyrr-based ionic liquids were obtained in our study for the first time and will be useful for designing of a new nanostructured hybrid materials with promising properties.

Role of Hydrogen Bond Defects for Cluster Formation and Distribution in Ionic Liquids by Means of Neutron Diffraction and Molecular Dynamics Simulations.

Defects fundamentally govern the properties of all real materials. Correlating molecular defects to macroscopic quantities remains a challenge, particularly in the liquid phase. Herein, we report the influence of hydrogen bonds (HB) acting as defects in mixtures of non-hydroxyl-functionalized ionic liquids (ILs) with an increasing concentration of hydroxyl-functionalized ILs. We observed two types of HB defects: The conventional HBs between cation and anion (c-a), and the elusive HBs between cations (c-c) despite the repulsive Coulomb forces. We use neutron diffraction with isotopic substitution in combination with molecular dynamics simulations for measuring the geometry, strength, and distribution of mobile OH defects in the IL mixtures. In principle, this procedure allows relating the number and stability of defects to macroscopic properties such as diffusion, viscosity, and conductivity, which are of utmost importance for the performance of electrolytes in batteries and other electrical devices.

Thermomechanical properties of imidazolium ionic liquid-modified mwcnt/carbon fiber/epoxy hybrid composite laminates

Hybrid composite laminates with nanofillers are high performance materials for thermal and structural applications. In this work, multiwall carbon nanotubes (MWCNT) were non-covalently modified by treating them with 1 wt% or 5 wt% of ionic liquid (IL), 1-butyl-3-methylimidazolium chloride. The treated MWCNT were dispersed in epoxy resin (weight content: 0.2–2 wt% or 1 to 3 wt%, respectively) and used to obtain hybrid composite laminates based on carbon fibers (CF) molded by hand layup and vacuum bagging techniques. The hybrid composite laminate containing 1 wt% of MWCNT modified with 1 wt% of IL showed the best mechanical and thermomechanical properties, including an increase of 210% and 151% in flexural strength and modulus, and an increase of 101%, 116% and 29.3% in storage modulus, loss modulus and damping, respectively. Scanning and transmission electron micrographs showed the enhanced MWCNT dispersion and network at low IL content, justifying its improved mechanical properties. The application of a low amount of IL dispersant was found a promising approach to prepare MWCNT/CF/epoxy composites with enhanced properties.

Lignosulfonate-Based Ionic Liquids as Asphaltene Dispersants.

Asphaltenes are recognized as being troublesome from upstream to downstream in the oil industry due to their tendency to precipitate and self-associate. Their extraction from asphaltenic crude oil for a cost-effective refining process is a crucial and critical challenge in the oil and gas sector. Lignosulfonate (LS), as a by-product of the wood pulping process in the papermaking industry, is a highly available and underutilized feedstock. This study aimed to synthesize novel LS-based ionic liquids (ILs) by reacting lignosulfonate acid sodium salt [Na]2[LS] with different alkyl chains of piperidinium chloride for asphaltene dispersion. The synthesized ILs, 1-hexyl-1-methyl-piperidinium lignosulfonate [C6C1Pip]2[LS], 1-octyl-1-methyl-piperidinium lignosulfonate [C8C1Pip]2[LS], 1-dodecyl-1-methyl-piperidinium lignosulfonate [C12C1Pip]2[LS] and 1-hexadecyl-1-methyl-piperidinium lignosulfonate [C16C1Pip]2[LS] were characterized using FTIR-ATR and 1H NMR for functional groups and structural confirmation. The ILs depicted high thermal stability because of the presence of a long side alkyl chain and piperidinium cation following thermogravimetric analysis (TGA). Asphaltene dispersion indices (%) of ILs were tested by varying contact time, temperature and ILs concentration. The obtained indices were high for all ILs, with a dispersion index of more than 91.2% [C16C1Pip]2[LS], representing the highest dispersion at 50,000 ppm. It was able to lower asphaltene particle size diameter from 51 nm to 11 nm. The kinetic data of [C16C1Pip]2[LS] were consistent with the pseudo-second-order kinetic model. The dispersion index (%), asphaltene particle growth and the kinetic model agreed with the molecular modeling studies of the HOMO-LUMO energy of IL holds.

Functionalized Graphene from Electrochemical Exfoliation of Graphite toward Improving Lubrication Function of Base Oil

Electrochemical exfoliation of graphene is an environmentally friendly method, which enables mass production. Herein, three ionic liquids (ILs) with the same imidazole cation were used to exfoliate graphite into functionalized graphene, as a lubricant additive in an acetonitrile solution. Chemical and structural characterization revealed the relationship between the functionalization density of graphene and the concentration of IL, showing higher concentrations with higher densities. The exfoliated graphene hybrid oil displayed good dispersion because of a high functionalization density. More importantly, the different anions affected the tribological properties of the exfoliated graphene. Among them, the exfoliated graphene with 1-butyl-3-methylimidazolium hexafluorophosphate ([BMIm][PF6]) possessed the best tribological performance, and the average friction coefficient and wear volume were reduced by 32% and 39%, respectively. Through the characterization of worn surfaces and wear debris, the lubrication mechanism and structural evolution of the functionalized graphene were illustrated in detail. The good lubrication function was attributed to the formation of a tribo-film and the disorder transformation of the graphene structure. The simultaneous exfoliation and functionalization of graphene offers a promising advanced lubricant for industrial fabrication.

Evaluation of structure-reactivity correlation of efficient corrosion inhibitor ionic liquids for mild steel in acidic medium

The synthesis and characterization of Imidazolium cation-based ionic liquids having different anions were reported in the present article. The physicochemical and spectral analyses were used to characterized these ionic liquids. The theoretical studies using the B3LYP method provide optimized structure, HOMO–LUMO plots, thermodynamic parameters, and quantum descriptors. The anti-corrosive property of Imidazolium cation-based ionic liquids was observed in 0.5 M H2SO4 corrosive medium at 303, 313, 323, and 333 K temperatures by various strategies like gravimetric studies, electrochemical impedance spectroscopy, potentiodynamic polarization studies, and scanning electron microscopy (SEM). The interesting feature of this article is that both ionic liquids follow different adsorption isotherms. IL-1 ionic liquid shows physisorption adsorption behavior, and IL-2 exhibits mixed adsorption (chemisorptions and physiorption). The electrochemical strategies and E gap value obtained from DFT reveal the maximum inhibition efficiency of IL-2 for the corrosion process in an acidic medium on mild steel. Potentiodynamic polarization studies reveal the mixed type behavior for ionic liquid inhibitors. EIS results indicate that the inhibition efficiency improved by enhancing ionic liquids concentration. The protective layer formation or adsorption of ionic liquid on metallic surface was confirmed by SEM. In the present article, the proposed mechanism shows the blockage of anodic and cathodic sites by ionic liquids to inhibit the corrosion process on mild steel in an acidic medium.

Investigation into the possibility of using a novel ionic liquid leaching method to obtain vanadium from vanadium slag

An environmentally friendly, novel method for extracting vanadium from slag with two imidazolium-based ionic liquids, namely1-butyl-3-methylimidazolium trifluoromethane sulfonate [Bmim+CF3SO3-], and 1-butyl-3-methyl-imidazolium hydrogen sulfate [Bmim+HSO4-], before and after magnetic separation, was proposed in this study. The effect of the type of ionic liquid, the concentration of ionic liquid, temperature and liquid to solid ratio were examined. The optimum experimental condition after examining these influential factors was found to be: ionic liquid [Bmim+HSO4–] 50% (v/v), a leaching temperature of 100 ℃, and a liquid to solid ratio of 12 ml/g (12:1), at a leaching time of 90 min, with shaking speed of 250 rpm. The results indicated that a maximum vanadium extraction of 94.2% with 57.6% iron as an impurity could be achieved from the non-magnetic slag fraction. The kinetics of vanadium dissolution in 50% (v/v) [Bmim+HSO4–] was governed by a surface chemical reaction with an estimated Ea= 65.5 kJ/mol.

Preparation of Cellulose Nanocrystals by Synergistic Action of Ionic Liquid and Recyclable Solid Acid under Mild Conditions

Cellulose nanocrystals (CNCs) are nanoscale particles made from cellulose. They have many unique properties such as being lightweight, stiff, and renewable, making them promising for a variety of applications in a wide range of industries, including materials science, energy storage, and biomedicine. In this paper, a two-stage (swelling-SA-catalyzed) method including IL pretreatment and solid acid hydrolysis process was developed to extract CNCs with high purity and good thermal stability from microcrystalline cellulose (MCC). In the first stage, the swelling of MCC in ionic liquid was studied with the assistance of ultrasonication, and it was found that the amorphous regions became more disordered while the crystalline areas were selectively retained under the conditions of 30 min of reaction time, 45 °C of temperature, 2% of ionic liquid water content and 1:4 mass ratio of cellulose to ionic liquid. CNCs were extracted using solid acid hydrolysis, with a 45 wt% solid acid to cellulose ratio and a 5.0 h hydrolysis process at 45 °C. The morphology, crystallinity, surface characteristics and thermo stability of the sample were characterized by atomic force microscopy (AFM), X-ray diffraction (XRD) and thermogravimetric analysis (TGA), respectively. Results demonstrated the highly thermostable CNCs were successful extracted with rodlike shape of 300 ± 100 nm in length and 20 ± 10 nm in width. Solid acid recovery and reuse were also studied, revealing a promising candidate that can reduce the environmental impact associated with chemical products.

Novel Oxygen- and Curcumin-Laden Ionic Liquid@Silica Nanocapsules for Enhanced Antimicrobial Photodynamic Therapy.

The efficiency of photodynamic therapy is often limited by the scarcity of oxygen at the target site. To address this problem, this work proposes the development of a new nanosystem for antimicrobial photodynamic therapy applications (aPDT) where the natural-origin photosensitizer curcumin (CUR) is immersed in an oxygen-rich environment. Inspired by the perfluorocarbon-based photosensitizer/O2 nanocarriers reported in the literature, we developed a new type of silica nanocapsule containing curcumin dissolved in three hydrophobic ionic liquids (ILs) with high oxygen dissolving capacities. The nanocapsules (CUR-IL@ncSi), prepared by an original oil-in-water microemulsion/sol-gel method, had a high IL content and exhibited clear capacities to dissolve and release significant amounts of oxygen, as demonstrated by deoxygenation/oxygenation studies. The ability of CUR-IL solutions and of CUR-IL@ncSi to generate singlet oxygen (1O2) upon irradiation was confirmed by the detection of 1O2 phosphorescence at 1275 nm. Furthermore, the enhanced capacities of oxygenated CUR-IL@ncSi suspensions to generate 1O2 upon irradiation with blue light were confirmed by an indirect spectrophotometric method. Finally, preliminary microbiological tests using CUR-IL@ncSi incorporated into gelatin films showed the occurrence of antimicrobial effects due to photodynamic inactivation, with their relative efficiencies depending on the specific IL in which curcumin was dissolved. Considering these results, CUR-IL@ncSi has the potential to be used in the future to develop biomedical products with enhanced oxygenation and aPDT capacities.

Experimental Study on CH4 Hydrate Dissociation by the Injection of Hot Water, Brine, and Ionic Liquids

Thermal stimulation is an important method to promote gas production and to avoid secondary hydrate formation during hydrate exploitation, but low thermal efficiency hinders its application. In this work, hydrate dissociation was carried out in synthesized hydrate-bearing sediments with 30% hydrate saturation at 6.9 MPa and 9 °C. Ionic liquids, such as 1-butyl-3-methylimidazolium chloride (BMIM-Cl) and tetramethylammonium chloride (TMACl), were injected as heat carriers, and the promotion effects were compared with the injection of hot water and brine. The results showed that the injection of brine and ionic liquids can produce higher thermal efficiencies compared to hot water. Thermodynamic hydrate inhibitors, such as NaCl, BMIM-Cl, and TMACl, were found to impair the stability of CH4 hydrate, which was conducive to hydrate dissociation. By increasing the NaCl concentration from 3.5 to 20 wt%, the thermal efficiency increased from 37.6 to 44.0%, but the thermal efficiencies experienced a fall as the concentration of either BMIM-Cl or TMACl grew from 10 to 20 wt%. In addition, increasing the injection temperature from 30 to 50 °C was found to bring a sharp decrease in thermal efficiency, which was unfavorable for the economics of gas production. Suitable running conditions for ionic liquids injection should control the concentration of ionic liquids under 10 wt% and the injection temperature should be around 10 °C, which is conducive to exerting the weakening effect of ionic liquids on hydrate stability.

Intermolecular Interactions and Electrochemical Studies on Highly Concentrated Acetate-Based Water-in-Salt and Ionic Liquid Electrolytes

Water-in-salt electrolytes constitute a new class of materials that have distinct properties relative to lower-concentration solutions. A recent approach to further increase the salt concentration and decrease the water content includes the addition of an ionic liquid to a highly concentrated aqueous solution. However, the physicochemical and electrochemical properties of aqueous lithium acetate-1-ethyl-3-methylimidazolium acetate solutions as well as the molecular interactions between electrolyte species have not been characterized. Here, we investigate these properties by evaluation of the ionic conductivity, viscosity, and thermal properties as well as the electrochemical behavior of various electrodes in these electrolytes. The intermolecular interactions are probed by nuclear magnetic resonance and infrared spectroscopies. We find that the addition of the ionic liquid increases the solubility limit of lithium acetate and that with an increase in both acetate salt and ionic liquid concentration in the electrolyte and decrease in water concentration, a strong acetate-water network is formed. The electrochemical stability window increases upon addition of the ionic liquid and reaches a value larger than 5 V for a set of negative Al and positive Ti electrodes in the highest acetate salt/ionic liquid concentration. Preliminary electrochemical charge storage performance measurements of a symmetric device based on two porous carbon electrodes cycled at a current density of 25 mA g-1 delivered a specific capacitance of 20 F g-1 with a Coulombic efficiency higher than 99% using a 1.8 V voltage window.

Cross-Link-Dependent Ionogel-Based Triboelectric Nanogenerators with Slippery and Antireflective Properties.

Given the ability to convert various ambient unused mechanical energies into useful electricity, triboelectric nanogenerators (TENGs) are gaining interest since their inception. Recently, ionogel-based TENGs (I-TENGs) have attracted increasing attention because of their excellent thermal stability and adjustable ionic conductivity. However, previous studies on ionogels mainly pursued the device performance or applications under harsh conditions, whereas few have investigated the structure-property relationships of components to performance. The results indicate that the ionogel formulation-composed of a crosslinking monomer with an ionic liquid-affects the conductivity of the ionogel by modulating the cross-link density. In addition, the ratio of cross-linker to ionic liquid is important to ensure the formation of efficient charge channels, yet increasing ionic liquid content delivers diminishing returns. The ionogels are then used in I-TENGs to harvest water droplet energy and the performance is correlated to the ionogels structure-property relationships. Improvement of the energy harvesting is further explored by the introduction of surface polymer brushes on I-TENGs via a facile and universal method, which enhances droplet sliding by means of ideal surface contact angle hysteresis and improves its anti-reflective properties by employing the I-TENG as a surface covering for solarcells.