Ionic Liquid Gel Research Articles

A scalable nano-engineering method to synthesize 3D-graphene-carbon nanotube hybrid fibers for supercapacitor applications

In this work, we describe a simple approach for the synthesis of three-dimensional graphene (3D-G) - carbon nanotube (CNT) hybrid fibers via Chemical Vapor Deposition (CVD). The obtained hybrid fiber was employed as a free-standing current collector in an electrochemical supercapacitor thus avoiding any conductive additives or metals. The amount of graphene synthesized on the CNT fiber and its properties have been easily tuned by different processing parameters, as described in the paper below. The fabricated fibers revealed a reasonable mechanical strength of 220.4 MPa and high electrical conductivity up to 649 Scm−1. They also showed excellent electrochemical properties and capacitance that was important for their energy storage application. Interconnected PANI nanorods were grown on these fibers by oxidation polymerization, and the resulted fibrous hybrid structures were used as electrodes to make supercapacitors. The created devices employed an ionic liquid gel electrolyte (PVDF-EMIMBF4) which had a voltage window of 3.2 V, thus increasing significantly the energy densities of the supercapacitors. The tested devices achieved a gravimetric energy density of 12.93 Wh/kg and a power density of 1350.25 W/kg at a current density of 1 A/g. They also demonstrated an areal energy density of 14.54 μWh/cm2 and a power density of 1.37 mW/cm2 at a current density of 1 mA/cm2.

Application and Analysis of an Ionic Liquid Gel in a Soft Robot

Due to their light weight, flexibility, and low energy consumption, ionic electroactive polymers have become a hotspot for bionic soft robotics and are ideal materials for the preparation of soft actuators. Because the traditional ionic electroactive polymers, such as ionic polymer-metal composites (IPMCs), contain water ions, a soft actuator does not work properly upon the evaporation of water ions. An ionic liquid polymer gel is a new type of ionic electroactive polymer that does not contain water ions, and ionic liquids are more thermally and electrochemically stable than water. These liquids, with a low melting point and a high ionic conductivity, can be used in ionic electroactive polymer soft actuators. An ionic liquid gel (ILG), a new type of soft actuator material, was obtained by mixing 1-butyl-3-methylimidazolium tetrafluoroborate (BMIMBF4), hydroxyethyl methacrylate (HEMA), diethoxyacetophenone (DEAP) and ZrO2 and then polymerizing this mixture into a gel state under ultraviolet (UV) light irradiation. An ILG soft actuator was designed, the material preparation principle was expounded, and the design method of the soft robot mechanism was discussed. Based on nonlinear finite element theory, the deformation mechanism of the ILG actuator was deeply analyzed and the deformation of the soft robot when grabbing an object was also analyzed. A soft robot was designed with the soft actuator as the basic module. The experimental results show that the ILG soft robot has good driving performance, and the soft robot can grab a 105 mg object at an input voltage of 3.5 V.

High-Performance Ionic Liquid Gel Polymer Electrolytes for Solid-State Lithium Metal Batteries

Lithium metal is considered as a “Holy Grail” anode material for secondary batteries because of its extremely high theoretical specific capacity (3860 mA h g−1), low electrochemical potential (-3.04 V vs. SHE), and low density (0.59 g cm-3). Ionically conductive polymer electrolytes represent a class of environmental-friendly and inflammable electrolytes for solid-state batteries that can enable the use of lithium metal. In our study, we fabricated lithium metal batteries based on transparent self-standing ionic liquid gel polymer electrolytes (ILGPEs) and LiFePO4cathodes. We evaluated the properties of ILGPEs by engineering the compositional space between the constituting components: poly(vinylidene fluoride-co-hexafluoropropylene) (PVDF-HFP), N-methyl-N-propylpiperidinium bis(trifluoromethanesulfonyl)imide (PP13TFSI), and lithium bis(trifluoromethanesulfonyl)imide (LiTFSI). The ionic conductivity of ILGPE increases with the increase of PP13TFSI and LiTFSI, and a maxima conductivity was obtained when the mass ratio of PP13TFSI, PVDF-HFP, and LiTFSI was 3:1:1, and the value was 1.3 mS cm-1at 22 ºC, and then increased to 5.82 mS cm-1at 80 °C. The optimized ILGPE showed excellent compatibility with lithium metal, determined by the interfacial resistance stability with the elapsed time. The solid-state LiFePO4cells delivered a practical capacity approaching 89.5% of the theoretical capacity and a capacity retention of 95.1% after 200 cycles with a current density of C/5 at 22 ºC. The solid-state lithium metal batteries using various cathodes materials, such as NMC, Co-free layered oxides, disordered rocksalt were also evaluated.

Unveiling of the energy storage mechanisms of multi -modified (Nb2O5@C)/rGO nanoarrays as anode for high voltage supercapacitors with formulated ionic liquid electrolytes

A better understanding of the energy-storage mechanisms in complex pseudocapacitive nanostructures is essential to improve the performances of nanohybrid supercapacitors. In this study, highly interface modified Nb2O5 nanoarrays, attached to graphene nanosheets, were carefully designed and synthesized. The electrochemical performances were evaluated in an organic electrolyte, a formulated ionic-liquid mixture electrolyte, and a nanocomposite ionogel electrolyte, respectively. The capacitive and faradaic storage contributions were assessed qualitatively in diverse electrolytes at various temperatures. The capacitive contribution in the ionic liquid electrolyte was found to rise with increasing temperature. A molecular dynamics simulation proved that the increased diffusion coefficient of large ions was much more pronounced than that of the small Li+ ions. A carefully optimized quasi-solid-state lithium ion capacitor, fabricated using a (Nb2O5@C)/rGO nanoarchitecture as the anode and an ionic liquid gel separator, delivered an energy density of 101 Wh kg−1 and a power density of 24 kW kg−1 at 60 °C. The efficient coupling between the nanohybrids and a complex ionogel electrolyte opens a new window for the rational design of high energy-density supercapacitors.

Hierarchical MnO2/activated carbon cloth electrode prepared by synchronized electrochemical activation and oxidation for flexible asymmetric supercapacitors

Despite appealing supercapacitive properties, the flexible asymmetric supercapacitor devices (FASCs) are still suffering from low mass loading and limited operating voltage, leading to unsatisfactory energy densities. Herein, we introduced a high-voltage anodic electro-deposition process (AED) which is a novel avenue enabling the synthesis of hierarchical MnO2 on activated carbon cloth (H-MnO2/ACC). Interestingly, the concomitant activation of carbon cloth substrate is found to be beneficial to improve the conductivity and hydrophilic nature of our novel electrode. A FASC based on H-MnO2/ACC-300 and reduced carbon cloth (RCC) was assembled using a mixed ionic liquid gel (ionogel) electrolyte. Benefiting from highly conductive paths derived from intimately attached fiber-MnO2 interfaces, hierarchically interpenetrated lamella MnO2 porosity and concentric MnO2 interlayer voids, as well as the merits of ionic liquid, the resultant FASC delivers an output voltage as high as 4 V and an impressive volumetric energy density of 3.82 mWh/cm3. Furthermore, the optimized H-MnO2/ACC-300 electrode with high mass loading can even retain 94.2% of initial capacitance upon 5000 cycles in 1 M Na2SO4. The unique H-MnO2/ACC can aid in the rational design towards flexible electronic devices with high mass loading and this synthetic strategy opens up enormous possibilities for the fabrication of electrodeposited materials.

Ionic Liquid Gels: Supramolecular Reaction Media for the Alcoholysis of Anhydrides.

The search of new enantioselective catalysts, able to promote synthetically useful organic reactions with high levels of asymmetric induction, should be associated with the attention to the suitable reaction medium able to achieve the best efficiency in chemical processes. We have investigated the enantioselective desymmetrization of cyclic meso-anhydrides in nonconventional reaction media such as ionic liquids and supramolecular gels. With this aim, we examined several variables in the reacting system: the nature of ionic liquid used as the reaction medium, the gelation solvent, the structure of the anhydrides, the structure of alcohols, the chiral catalysts, and the reaction conditions, i.e., temperature and time. The different components of the system differently influence the reaction outcome, and to understand the interactions existing among them, 1H NMR investigation was carried out. In general, the nonconventional reaction media demonstrated better performance than conventional ones, applying only a small amount of solvent. Good results in terms of yield and enantiomeric excess have been obtained in ionic liquid gels that seem promising media in the catalytic field. Furthermore, to the best of our knowledge, this is one of the first examples for the study of asymmetric alcoholysis of anhydrides in ionic liquid solution and gel phase.

Solid-state graphene-based supercapacitor with high-density energy storage using ionic liquid gel electrolyte: electrochemical properties and performance in storing solar electricity

The electrochemical properties and high-density energy storage performance of graphene nano-platelet-based solid-state electrical double-layer supercapacitor device are reported. The graphene device is fabricated with electrolyte comprising of 1-butyl-3-methylimidazolium tetrafluoroborate (BMIMBF4) room temperature ionic liquid and LiClO4 dopant entrapped within polymer matrix formulated as a gel. The mesoporous graphene electrode was formed via dispersion in amorphous polyvinylidene (PVdF2) host over flexible graphite sheets with minimal graphene layer (< 5-layer) stacking. Exploiting the abundance of charge ion species in the ionic liquid gel electrolyte and pervasive accesses to the graphene platelets via voids, high double-layer specific capacitance of 214 Fg−1 was realized based on cyclic voltammetry data. Impedance studies show a low (0.79 Ω cm2) charge transfer resistance and a short Warburg range indicating highly diffusive ionic transport capability in the ionic liquid gel electrolyte. The Bode analysis showed high figure of merit for pulse power with 1145 ms response time and high-density (27 kWkg−1) pulsed power capability of the graphene supercapacitor. The charge–discharge data show graphene supercapacitor by availing high (~ 2 V) stable potential window in ionic liquid electrolyte gel greatly boosted the energy density to 33.3 Whkg−1 at power density 3 kWkg−1 with minimal decrement to 24.7 Whkg−1 at high ~ 3 Ag−1 discharge current density. By integration with solar cells, direct storage of light-generated electricity and discharge behavior of ionic liquid electrolyte graphene supercapacitor is reported.

Electrochemical and electromechanical properties of high-performance fluoropolymer/ionic liquid (with wide electrochemical window of 6 V) gel hybrid actuators based on single-walled carbon nanotubes

In this study, various ionic liquids (ILs) with electrochemical windows as wide as 6 V were synthesized and their electrochemical and electromechanical properties were evaluated for their application in actuators. These actuators were based on an ionic fluoropolymer (Nafion™)/non-ionic fluoropolymer (poly(vinylidene fluoride‑co‑hexafluoropropylene) [PVdF(HFP)]) gel fabricated using a single-walled carbon nanotube (SWCNT) containing an ionic liquid (IL) gel electrode, which was in turn composed of aliphatic or cyclic quaternary cations and perfluoroalkyltrifluoroborate anions. The ionic conductivity of the gel electrolyte layer was dependent on the IL species employed. In addition, the maximum strains of the ±3-V actuators were 1.5–2-times larger than those of the ±2-V actuators. These results indicated that the Nafion™/PVdF(HFP)-based hybrid actuators, containing quaternary cations and perfluoroalkyltrifluoroborate anions, are ideal for practical applications and could be used as electrochemical materials in wearable and energy conversion devices. After determining the frequency dependences of the displacement responses of the above-mentioned Nafion™/PVdF(HFP)–SWCNT–IL gel hybrid actuators, these results were simulated using a double-layer charging kinetic model. Surprisingly, the simulated curves were similar and comparable to the experimentally obtained ones. The response time constant was determined and was represented by an equivalent circuit comprising a series combination of the ionic resistances and the double-layer capacitance. The Nafion™/PVdF(HFP)–SWCNT–IL (imidazolium-cation-type) gel hybrid actuator was represented by the ionic resistance and double-layer capacitance, in contrast to the PVdF(HFP)–SWCNT–IL (imidazolium-cation-type) actuator, which was represented by the electronic resistance and double-layer capacitance.

Motion Simulation of Ionic Liquid Gel Soft Actuators Based on CPG Control.

The ionic liquid gel (ILG), a new type of soft actuator material, is a mixture of 1-butyl-3-methylimidazolium tetrafluoroborate (BMIMBF4), hydroxyethyl methacrylate (HEMA), diethoxyacetophenone (DEAP), and ZrO2 polymerized into a gel state under ultraviolet (UV) light irradiation. The soft actuator structure consists of a layer of ionic liquid polymer gel sandwiched between two layers of activated carbon capped with gold foil. The volume of the cationic BMIM+ in the ionic liquid BMIMBF4 is much larger than that of the anionic BF4 −. When voltages are applied to both sides of the actuator, the anions and cations move toward the anode and cathode of the electrode, respectively, under the electric field. The volume of the ILG cathode side therefore expands, and the volume of the ILG anode side shrinks, hence bending the entire actuator toward the anode side. The Ogden model was selected as the hyperelastic constitutive model to study the mechanical properties of the ILG by nonlinear analysis. As the ILG is an ideal material for the preparation of a supercapacitor, the equivalent circuit of the ILG can be modeled by the supercapacitor theory to identify the transfer function of the soft actuator. The central pattern generator (CPG) control is widely used in the area of biology, and CPGs based on bioinspired control methods have attracted great attention from researchers worldwide. After the continuum soft actuator is discretized, the CPG-based bioinspired method can be used to control the soft robot drivers. According to the simulation analysis results, the soft actuator can be smooth enough to reach the specified location.

Electric-field effect on photoluminescence of lead-halide perovskites

With the development of novel semiconductors for optoelectronic applications, new device functionalities utilizing unique characteristics of emerging materials can be particularly appealing. Here, we demonstrate a reversible control of photoluminescence (PL) emission from lead-halide perovskites achieved in perovskite electric-double-layer transistors. PL in several prototypical lead-halide perovskite compounds is shown to be reversibly tuned by a small gate voltage in the range ±1.2 V applied to the ionic-liquid gel on the perovskite surface, with the intensity modulation that can reach one to two orders of magnitude. This effect may be mediated by a reversible migration of oxygen ions affecting the crystal region near the interface with the ion gel. The resulting passivation (or activation) of non-radiative recombination centers (traps) by oxygen ions would then modulate the population of mobile photogenerated electrons and holes that give rise to PL, which is thus tuned with an electric “knob” (the gate) in these devices.

Supported Ionic Liquid Gel Membrane Electrolytes for a Safe and Flexible Sodium Metal Battery

Concerns about the sustainability of lithium supplies has stimulated interest in alternative energy storage chemistries including in sodium metal and sodium ion batteries. Gel ionic liquid electrol...

An ionic liquid gel with ultralow concentrations of tetra-arm polymers: Gelation kinetics and mechanical and ion-conducting properties

We report an ion gel with ultralow polymer content based on two key materials: 1 wt% tetra-arm poly(ethylene glycol) (TetraPEG) and 99 wt% ionic liquid (herein, 1-ethyl-3-methylimidazolium bis(fluorosulfonyl)amide, [C2mIm][FSA]). We performed kinetics analysis on the TetraPEG network formation in [C2mIm][FSA], i.e., AB-type cross-end coupling reaction of two different TetraPEGs with thiol (SH) and maleimide (MA) terminals (TetraPEG-SH and TetraPEG-MA). In neat [C2mIm][FSA], no gelation occurred at room temperature, whereas the reaction successfully proceeded when 1-ethylimidazole (C2Im) was added in this reaction as a catalyst. The apparent reaction rate constant (k′gel) was determined by varying C2Im concentration, and the network connectivity (p) was estimated to be p ∼ 98% toward the end of the reaction. The results indicated that the TetraPEG prepolymers could be successfully gelled in [C2mIm][FSA] despite extremely low polymer content (1 wt%), which allows us to prepare an ideally homogeneous polymer network gel with a large amount of ionic liquid. The ionic conductivity measurements demonstrated that the 1 wt% TetraPEG ion gel showed ideal liquid-like ion-conducting properties that were comparable to those of neat ionic liquid.

Synthesis of Benzoxazoles, Benzimidazoles, and Benzothiazoles Using a Brønsted Acidic Ionic Liquid Gel as an Efficient Heterogeneous Catalyst under a Solvent-Free Condition.

Herein, we introduce a reusable Brønsted acidic ionic liquid gel (BAIL gel) obtained by treating 1-methyl-3-(4-sulfobutyl)-1H-imidazolium hydrogen sulfate with tetraethyl orthosilicate (TEOS). The grafting of the Brønsted acidic ionic liquid to the surface of TEOS has increased the catalytic activity of the material and also simplified catalyst recovery from the reaction mixture. This reaction has a wide substrate scope, and the BAIL gel represents a new catalyst for the synthesis of benzoxazoles, benzimidazoles, and benzothiazoles. The method shows attractive characteristics such as high yields, recyclable catalyst, and work-up simplicity. More importantly, no additional additives or volatile organic solvent and inert atmosphere are required for the reaction, and the BAIL gel has shown a great promise for industrial applications. To the best of our knowledge, the synthesis of benzoxazoles, benzimidazoles, and benzothiazoles using a recyclable heterogeneous ionic liquid gel was not previously reported in the literature.

The alkylation of indole with benzaldehyde derivatives catalyzed by 1-(4- sulfobutyl)-3-methylimidazolium hydrogene sulfate ion gel

The alkylation of indole with benzaldehyde and derivatives catalyzed by 1-(4- sulfobutyl)-3-methylimidazolium hydrogene sulfate ion gel has been developed. The reaction was taken place under solvent-free ultrasonic irradiation afforded the corresponding product in high yield. Ion gel catalysis was formed by sol-gel method. The recovered ionic liquid gel in each reaction which is quite simply achieved by filtration could be reused up to 5 times without any detectable loss of catalytic performance.

Synthesis, characterization and properties of tropine-based ionic liquids gels

Hydrophilic ionic liquid (IL) gels based-on tropine as a potential separation material.

Basic Ionic Liquid Gels for Catalysis: Application to the Hydrogen Borrowing Mediated Dehydration of 1,3-Propanediol

The application of basic ionic liquid gels (BILGs) as recyclable promoters of hydrogen borrowing chemistry was investigated. The hydrogen transfer initiated dehydration of 1,3-propanediol to propan...

Effect of polymer type on the performance of a nanofiber mat actuator

We fabricated actuators consisting of an ionic liquid gel electrolyte layer sandwiched between two nanofiber mat electrodes and studied the relationship between the polymer type of the nanofiber mat and the performance of the actuator. We selected poly(urethane) (PU), poly(methyl methacrylate), and poly(vinylidene fluoride-co-hexafluoropropylene) (PVDF-HFP) as the materials for the nanofiber mat electrodes. The PU nanofiber mat actuator exhibited the largest deformation, whereas the PVDF-HFP mat actuator exhibited the smallest deformation. The performance of the actuator was determined on the basis of cyclic voltammetry and alternating current impedance measurements. We fabricated actuators consisting of an ionic liquid gel electrolyte layer sandwiched between two nanofiber mat electrodes and studied the relationship between the polymer type of the nanofiber mat and the performance of the actuator. We selected poly(urethane) (PU), poly(methyl methacrylate) (PMMA), and poly(vinylidene fluoride-co-hexafluoropropylene) (PVDF-HFP) as the materials for the nanofiber mat electrodes. The performance of the actuator was determined on the basis of cyclic voltammetry and AC impedance measurements.

High-performance N-methyl-N-propylpiperidinium bis(trifluoromethanesulfonyl)imide/poly(vinylidene fluoride-hexafluoropropylene) gel polymer electrolytes for lithium metal batteries

Ionically conductive polymer electrolytes represent a class of safe and environment-friendly electrolytes for next-generation alkali metal batteries. Understanding the interplay between composition-driven interfacial processes and battery performance can fundamentally inform the design of polymer electrolytes for practical applications. In this study, we fabricate lithium metal batteries based on transparent free-standing ionic liquid gel polymer electrolytes (ILGPEs) and LiFePO4 cathodes. We develop the ILGPEs using a composite of poly(vinylidene fluoride-co-hexafluoropropylene) (PVDF-HFP), N-methyl-N-propylpiperidinium bis(trifluoromethanesulfonyl)imide (PP13TFSI), and lithium bis(trifluoromethanesulfonyl)imide (LiTFSI). A thorough compositional optimization shows that the lithium ion conductivity of the ILGPE increases with the increase of PP13TFSI and LiTFSI, reaching maxima of 1.3 mS cm−1 at 23 °C and 5.82 mS cm−1 at 80 °C when the ILGPE contains 60 wt% PP13TFSI and 20 wt% LiTFSI. The optimized ILGPE exhibits excellent interfacial stability against the lithium metal, as signified by the stable interfacial resistance upon long-term storage. The LiFePO4|ILGPE|Li cells can deliver superior battery performance with a practical capacity approaching 89.5% of the theoretical capacity and capacity retention of 95.0% after 200 cycles. The formation of the electrode–electrolyte interphases takes place primarily during the initial cycles, which likely accounts for the activation period observed in LiFePO4|ILGPE|Li cells.

Thin‐Film Composite Polyionic Liquid Gel Membranes and Their Potential for Nanofiltration in Organic Solvents

AbstractPolymeric ionic liquid (PIL) gels can serve as a promising material for the fabrication of solvent resistance nanofiltration (SRNF) membranes, given the solubility and the high delocalization of the counterion of PILs in organic solvents. This research describes the fabrication of a new thin‐film composite membrane (TFC) with a crosslinked PIL (i.e., PIL gel) as an active layer and demonstrates its great potential as an SRNF membrane. A hydrophobic and positively charged thin‐film PIL gel (100–400 nm) is successfully grafted onto a polyethersulfone membrane. The grafting degree, surface charge, and cross‐linker density depend on the grafting conditions. This, it turn, governs the permeability and selectivity of the membranes tested in acetonitrile and ethanol solutions, good and poor solvents for the grafted PIL gel, respectively. These changes are attributed to the trade‐off between the membrane surface properties in the two solvents. In particular, the membrane that has a high grafting degree, surface charge, and cross‐linker density yields high permeance and rejection in acetonitrile. Furthermore, the membrane performance is stable in ethanol for one week. Due to the wide variety of PIL monomers, TFC membranes with different properties can be developed based on the solvent properties.

Solid-state supercapacitors based on poly (3, 4-ethylendioxythiophene) (PEDOT) – Manganese oxide (MnO2) composite electrodes synthesized by single-step Co-Deposition for electrical energy storage

In this work, solid-state supercapacitors were fabricated and characterized based on PEDOT-MnO2 electrodes and ionic liquid gel polymer electrolyte. The PEDOT-MnO2 electrodes were synthesized by single-step co-deposition technique in an aqueous solution consisting of 0.1 M LiClO4, 0.01 M EDOT monomer, 0.07 M SDS, and 0.3 M MnSO4. For comparative studies, another electrode was prepared from pure MnO2 that was electrochemically synthesized in exact same way with the exception that the EDOT monomer was not dissolved in the electrochemical deposition aqueous medium. The presence of both PEDOT and MnO2 in the electrochemically prepared electrodes was confirmed by Raman spectroscopy. The electrochemical performance characteristics were evaluated using cyclic voltammetry, charge-discharge tests, and electrochemical impedance spectroscopy. The PEDOT-MnO2 solid-state supercapacitor displayed an optimum areal capacitance density of 73.81 mF cm−2 at 10 mV s−1. The maximum energy and power densities were found to be 15.07 Wh kg−1 and 6.84 kW kg−1, respectively. In addition, the electrochemical performance of both PEDOT-MnO2 and pure MnO2 based solid-state supercapacitors was compared in terms of CV and CD and it was confirmed that the PEDOT-MnO2 electrode had superior electrochemical performance compared to the pure MnO2 electrode. Overall, the PEDOT-MnO2 based solid-state supercapacitor holds great potential for thin, flexible, and lightweight energy storage.