Ionic Liquid Ions Research Articles

Computational predictions on Brønsted acidic ionic liquid-catalyzed carbon dioxide conversion to five-membered heterocyclic carbonyl derivatives.

Experimentally conducted reactions between CO2 and various substrates (i.e., ethylenediamine (EDA), ethanolamine (ETA), ethylene glycol (EG), mercaptoethanol (ME), and ethylene dithiol (EDT)) are considered in a computational study. The reactions were previously conducted under harsh conditions utilizing toxic metal catalysts. We computationally utilize Brønsted acidic ionic liquid (IL) [Et2NH2]HSO4 as a catalyst aiming to investigate and propose 'greener' pathways for future experimental studies. Computations show that EDA is the best to fixate CO2 among the tested substrates: the nucleophilic EDA attack on CO2 is calculated to have a very small energy barrier to overcome (TS1EDA, ΔG‡ = 1.4 kcal mol-1) and form I1EDA (carbamic acid adduct). The formed intermediate is converted to cyclic urea (PEDA, imidazolidin-2-one) via ring closure and dehydration of the concerted transition state (TS2EDA, ΔG‡ = 32.8 kcal mol-1). Solvation model analysis demonstrates that nonpolar solvents (hexane, THF) are better for fixing CO2 with EDA. Attaching electron-donating and -withdrawing groups to EDA does not reduce the energy barriers. Modifying the IL via changing the anion part (HSO4-) central S atom with 6 A and 5 A group elements (Se, P, and As) shows that a Se-based IL can be utilized for the same purpose. Molecular dynamics (MD) simulations reveal that the IL ion pairs can hold substrates and CO2 molecules via noncovalent interactions to ease nucleophilic attack on CO2.

Simulations of electric field gradient fluctuations and dynamics around sodium ions in ionic liquids.

The T1 relaxation time measured in nuclear magnetic resonance experiments contains information about electric field gradient (EFG) fluctuations around a nucleus, but computer simulations are typically required to interpret the underlying dynamics. This study uses classical molecular dynamics (MD) simulations and quantum chemical calculations, to investigate EFG fluctuations around a Na+ ion dissolved in the ionic liquid 1-ethyl 3-methylimidazolium tetrafluoroborate, [Im21][BF4], to provide a framework for future interpretation of NMR experiments. Our calculations demonstrate that the Sternheimer approximation holds for Na+ in [Im21][BF4], and the anti-shielding coefficient is comparable to its value in water. EFG correlation functions, CEFG(t), calculated using quantum mechanical methods or from force field charges are roughly equivalent after 200fs, supporting the use of classical MD for estimating T1 times of monatomic ions in this ionic liquid. The EFG dynamics are strongly bi-modal, with 75%-90% of the de-correlation attributable to inertial solvent motion and the remainder to a highly distributed diffusional processes. Integral relaxation times, ⟨τEFG⟩, were found to deviate from hydrodynamic predictions and were non-linearly coupled to solvent viscosity. Further investigation showed that Na+ is solvated by four tetrahedrally arranged [BF4]- anions and directly coordinated by ∼6 fluorine atoms. Exchange of [BF4]- anions is rare on the 25-50ns timescale and suggests that motion of solvent-shell [BF4]- is the primary mechanism for the EFG fluctuations. Different couplings of [BF4]- translational and rotational diffusion to viscosity are shown to be the source of the non-hydrodynamic scaling of ⟨τEFG⟩.

Mixed micelle formation by sodium dodecylsulfate and dodecyltrimethylammonium bromide in aqueous ionic liquid media

Surfactant self-aggregation within ionic liquid (IL) - based media has been investigated to compare and contrast the role of such media with that of water. Behavior of a surfactant mixture constituting of two surfactants with oppositely charged head groups, namely anionic sodium dodecylsulfate (SDS) and cationic n-dodecyltrimethylammonium bromide (DTAB), is assessed in aqueous IL media. Contrary to what is observed in water, it is shown earlier that effective charge screening of the surfactant headgroups by IL ions in a typical IL 1-ethyl-3-methylimidazolium ethylsulfate ([C2C1im][EtSO4]) results in formation of (SDS + DTAB) mixed micelles with critical micelle concentrations (CMCs) ranging between those of SDS and DTAB, respectively. The miscibility of (SDS + DTAB) mixture in aqueous [C2C1im][EtSO4] reveals that as the content of IL [C2C1im][EtSO4] is increased, the miscibility of the surfactant mixture improves indicating increased charge screening involving ions of the IL and the surfactant headgroups. For water mole fraction (XW) ≤ 0.90, (SDS + DTAB) surfactant mixture is miscible in aqueous [C2C1im][EtSO4] system in all proportions. For 1.00 ≥ XW≥ 0.90, while synergism persists due to the presence of attractive electrostatic attraction between SDS and DTAB headgroups leading to mixture CMCs below the CMCs of SDS and DTAB, respectively, the extent of synergism diminishes with increase in IL [C2C1im][EtSO4] in the solution. For XW = 0.80, the (SDS + DTAB) mixture exhibits CMC values that are closest to the values estimated assuming ideal behavior. For 0.70 ≥ XW ≥ 0.30, the (SDS + DTAB) exhibits antagonistic trend with CMC values higher than those estimated for ideal solution; the antagonistic trend gradually decreases with increase in [C2C1im][EtSO4] and again attains close to ideal behavior in neat IL [C2C1im][EtSO4]. This trend is subsequently manifested in the composition of the mixed micelles as well as in the net interaction parameter, β. Addition of small proportion of IL to water helps in solubilization of surfactant mixture of oppositely charged surfactants due to effective charge screening of the surfactant headgroups and results in formation of mixed micelles in aqueous IL media over complete composition range.

Extremely slow dynamics of ionic liquid self-assembled nanostructures near a solid surface

Hypothesis: The dynamics of the self-assembled liquid nanostructure of the ionic liquids (ILs) near a mica surface can be determined from video-rate atomic force microscopy (AFM) data.Experiments: Video-rate AFM has been used to record the nanostructure dynamics of two most widely studied ILs, 1-butyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide (BMIM TFSI) and ethylammonium nitrate (EAN), as well as EAN-water mixtures, above a model anode, mica. Diffusion coefficients were extracted from the AFM videos using dynamic differential microscopy and direct tracking.Findings: Video rate AFM is able to record the movement of the IL nanostructure. This is the first time that any liquid has been directly visualized at a scale of 10 nm × 10 nm in real-time. Diffusion coefficients determined from AFM videos reveal IL nanostructures near surfaces diffuse orders of magnitude more slowly than individual ions in the bulk. Thus, rather than free-flowing liquid, the near-surface nanostructure is better conceptualized as self-assembled aggregates of IL ions diffusing slowly over the cation-rich Stern layer, akin to adsorbed surfactant micelles in aqueous systems. This new and surprising insight affects wide-ranging processes involving the interfacial dynamics of concentrated electrolytes.

Deconvoluting the Combined Effects of Gas Composition and Temperature on Olefin Selectivity for Separations Using Silver(I) Ions in Ionic Liquids.

Silver(I) ions have the propensity of undergoing reduction to form metallic silver within olefin/paraffin separation systems when they are subjected to hydrogen at elevated temperatures. Ionic liquids (ILs) are versatile solvents known for their low vapor pressure, high thermal stability, and structural tunability and have been shown to minimize hydrogen-induced reduction of silver(I) ions when employed as solvents. In the development of robust separation platforms that employ silver(I) ions, it is essential to deploy reliable approaches capable of measuring and assessing the factors that lower the overall separation performance. In this study, silver(I) ions dissolved in an imidazolium-based IL are subjected to mixed gas streams composed of hydrogen, nitrogen, and methane under varying temperatures. Using inverse gas chromatography, a total of 44 columns with stationary phases containing four different concentrations of silver(I) bis[(trifluoromethyl)sulfonyl]imide ([Ag+][NTf2 -]) dissolved in the 1-decyl-3-methylimidazolium ([C10MIM+]) [NTf2 -] IL were used to measure partition coefficients of olefins and paraffins, as well as aromatics, esters, and ketones. Upon exposing the stationary phases to mixed gases at elevated temperatures, olefin partitioning between the silver(I) ion pseudophase and the two other phases (i.e., carrier gas and IL stationary phase) was observed to decrease over time, while partitioning between the IL stationary phase and carrier gas remained unchanged. It was found that exposure gases composed of 5.0 to 85.0 mol % hydrogen and temperatures ranging from 95 to 130 °C resulted in a remarkable acceleration of silver(I) ion reduction and an approximate 36.4-61.3% decrease in olefin partitioning between the silver(I) ion pseudophase and both the carrier gas and IL stationary phase after 60 h. While binary mixtures of hydrogen and nitrogen resulted in a continuous decrease in silver(I) ion-olefin complexation capability, a ternary gas mixture produced varied silver(I) ion reduction kinetics.

Correlation between Redox Potential and Solvation Structure in Biphasic Electrolytes for Li Metal Batteries.

The activity of lithium ions in electrolytes depends on their solvation structures. However, the understanding of changes in Li+ activity is still elusive in terms of interactions between lithium ions and solvent molecules. Herein, the chelating effect of lithium ion by forming [Li(15C5)]+ gives rise to a decrease in Li+ activity, leading to the negative potential shift of Li metal anode. Moreover, weakly solvating lithium ions in ionic liquids, such as [Li(TFSI)2 ]- (TFSI = bis(trifluoromethanesulfonyl)imide),increase in Li+ activity, resulting in the positive potential shift of LiFePO4 cathode. This allows the development of innovative high energy density Li metal batteries, such as 3.8V class Li | LiFePO4 cells, along with introducing stable biphasic electrolytes. In addition, correlation between Li+ activity, cell potential shift, and Li+ solvation structure is investigated by comparing solvated Li+ ions with carbonate solvents, chelated Li+ ions with cyclic and linear ethers, and weakly solvating Li+ ions in ionic liquids. These findings elucidate a broader understanding of the complex origin of Li+ activity and provide an opportunity to achieve high energy density lithium metal batteries.

Emission spectra of glows produced by ionic liquid ion sources

Electrospray devices, such as ionic liquid ion sources, often exhibit glows during operation in high vacuum facilities. The lack of electron excitation mechanisms during electrospray operation prompts the question: “What causes glow in an electrospray device?” Our optical emission spectroscopy results show that electrospray glow exhibits a broad spectral response between 350 and 800 nm with emission lines corresponding to atomic metal constituents of impinged surfaces, neutral and ionized atomic constituents of the ionic liquid propellant, and molecular line shapes that may also be dissociation products of the ionic liquid. We have previously defined secondary species emission to describe the many complex interfacial phenomena that occur when electrosprayed species impact surfaces downstream of the emitter. Our analysis of the optical emission spectra shows that these glows are only possible in the presence of secondary species emission. Therefore, the answer to the proposed question: high-velocity impacts that generate secondary species are the root cause of glow for electrosprays in high vacuum facilities.

(Invited) Understanding Transport Properties of Ionic Liquids By Targeted Modifications of Ion Structures

Ionic liquids have been of great interest throughout this century and continue to find new applications in both academia and industry. This is largely due to their great versatility, with millions of potential combinations of cations and anions, which has led to them being described as 'designer solvents'. However, this leads to its own problems when it comes to choosing the optimum ionic liquid for any given application. To fully exploit this versatility, it is imperative to understand how the properties of ionic liquids arise from their constituent ions.To derive meaningful structure-property relationships for ionic liquids is a complex task. It can be particularly difficult to isolate the cause of any property change arising from even simple modifications of ions. For example, changing the length of the alkyl chain of a cation in an ionic liquid also changes the volume and mass of the ion, all of which can affect a property such as ion mobility and consequent properties such as the viscosity and conductivity of the ionic liquid. A ‘targeted modification’ is a deliberate change in the structure of an ionic liquid ion that is designed to minimise the introduction of such confounding factors. The change must isolate what is of interest, so that we can study only one concept at a time. Once these structure-property relationships have been clearly defined, it will be possible to use these as design elements for new ionic liquids.As well as experimental observations, it is possible to apply the targeted modification approach to a computer simulation. This provides both insight into experimental observations and predictions of potential targeted modifications before complex synthesis is attempted. Together, theory and experiment will enable the concept of ionic liquids as designer solvents to be realised.In this presentation we apply the targeted modifications approach to the transport properties of ionic liquids.

The Puzzling Processes at Electrode | Ionic Liquid Interface

J.M. Lehn stated in his Nobel prize lecture in 1988 that supramolecular chemistry is the chemistry of the intermolecular bond, covering the structure and functions of entities formed by the association of two or more chemical species [1]. The adsorption of organic molecules is the net result of the interactions between the molecules and the two phases, the metal and the electrolyte, and the interactions between the latter two.To this day, the universal understanding that the adsorption of organic molecules results in the formation of an ordered monolayer is based on the phenomenon observed in mainly aqueous solutions. However, the conception might not be straightforwardly transferrable to the organic additive + ionic liquid | electrode interface. For example, the existence of an interfacial multilayer structure of pure IL ions in contrast with an aqueous electrolyte has been previously shown in both experimental and computational studies. Furthermore, it has been shown that in ILs, if the ions form rigid layers on the electrode, it is necessary to apply an overpotential for interfacial restructuring. Therefore, studying the adsorption of organic additives in ionic liquids (IL) should contribute to a better understanding of metal | IL interfaces.In the given presentation we overview the characteristics of solid-liquid interface characteristics of various additives from ionic liquid media at different electrodes.Cyclic voltammetry, electrochemical impedance spectroscopy and in situ scanning tunnelling microscopy measurements were conducted to characterize the electrochemical behavior of the self-assembled layers of 4,4’-bipyridine (4,4’-BP) and 2,2’-bipyridine (2,2’-BP) at the Sb(111) | x-BP+1-ethyl-3-methylimidazolium tetrafluoroborate (EMImBF4) interface [2-3]. The specific adsorption of iodide ions was studied at Bi(111), Cd(0001) and pyrolytic graphite electrodes [4-6]. All the experiments were carried out in a three-electrode electrochemical cell in a glovebox.The halide ions are surface active ions with specific adsorption behavior [4-6]. The strong specific adsorption of halide ions at single crystal electrodes, as well as other electrodes, is a complicated process due to the partial charge transfer between adsorbed ions and the solid electrode surface. The properties of the adsorption layer depend on the electrode potential and the concentration of the surface-active ions in an electrolyte. The theory that the adsorption of organic molecules results in SAM formation is mainly based on the results observed in aqueous solutions. However, these findings may not be as straightforwardly linkable to the organic additive + ionic liquid | electrode interface. The analysis of cyclic voltammetry and impedance results revealed that 2,2′-BP and 4,4′-BP indeed adsorb at the Sb(111) interface, forming a thin dielectric layer at the electrode surface, confirmed by in situ STM measurements, resulting in the differential capacitance values nearly two times lower compared to EMImBF4. Acknowledgments:This work was supported by the Estonian Research Council grant PSG249, and by the EU through the European Regional Development Fund under project TK141 (2014-2020.4.01.15-0011).

Accelerating effect of water on electroreduction of lanthanide ions in a dicyanamide ionic liquid: A generic phenomenon

• The electroreduction of Ln(III) to Ln(0) is described for six lanthanides in a dicyanamide IL. • Deposited Ln can be partly oxidized during electrodeposition by water in the solution. • Water accelerates the electroreduction of Ln(III) to Ln(0) in the dicyanamide IL. • The water accelerating effect is a generic phenomenon for the electroreduction of Ln. Electroplating is a relatively cheap and processible technique of metal production. In the case of lanthanides (Ln), however, this technology is inapplicable in water solutions due to their pronounced electropositivity. This work studies the electroreduction of lanthanides (Ln) from a dicyanamide ionic liquid (IL) on a model Pt(1 1 1) substrate in dry solutions and upon addition of controlled amounts of water. We demonstrate the possibility of irreversible electrodeposition for six different Ln from the dried IL using a complex set of electrochemical and physical (spectroscopic and microscopic) methods. Addition of water leads to the facilitation of electrodeposition for all the studied Ln, as confirmed by a positive shift in the deposition potentials. We relate this promoting effect to the coadsorption of water on the electrode surface and the relevant changes in the IL|electrode interface structure, e.g., the disordering of the IL multilayer structure at the electrode surface. We believe that this promoting effect of water is a generic phenomenon for Ln electrodeposition in dicyanamide ILs and discuss the possible causes that result in acceleration of deposition. Analysis of the obtained deposits indicates that the deposited Ln are partly oxidized in the course of the deposition even in dry solutions, probably due to interaction with the residual water. The results of this work may be instrumental in developing lanthanide electrowinning techniques based on mixtures of ionic organic solvents with controlled water additives.

Effects of Physicochemical Properties of Constituent Ions of Ionic Liquid on Its Permeation through a Silicone Membrane.

Ionic liquids (ILs), defined as liquid salts composed of anions and cations, have the advantage of allowing constituent ions to be stably absorbed through biological membranes, such as skin. However, limited information is currently available on the effects of the physicochemical properties of constituent ions on the membrane permeation of ILs. Therefore, we herein investigated the effects of the polarity of constituent cations on the membrane permeation of each constituent ion from IL. Various ILs were prepared by selecting lidocaine (LID) as a cation and a series of p-alkylbenzoic acids with different n-octanol/water partition coefficients (Ko/w) as anions. These ILs were applied to a skin model, a silicone membrane, and membrane permeability was investigated. The membrane permeabilities of p-alkylbenzoic acids from their single aqueous suspensions were also measured for comparison. The membrane permeability of p-alkylbenzoic acid from the aqueous suspension increased at higher Ko/w. However, the membrane permeability of ILs was similar regardless of the Ko/w of the constituent p-alkylbenzoic acid. Furthermore, the membrane permeability of the counterion LID remained unchanged regardless of the constituent p-alkylbenzoic acid. These results suggest that even when the Ko/w of IL constituents markedly differs, the resulting IL does not affect membrane permeability.

Analysis of impedance: The distribution of capacitance in halide ion treated supercapacitors

The micro- and mesoporous carbon electrode material has an enough pore width capacity to allow to adsorb the small-sized halide- and alkali ions, even to adsorb ionic liquid ions. • Ionic liquid mixtures containing halide or alkali ions are used to treat carbon electrodes. • The CV and EIS characteristics of carbon-based supercapacitors are studied. • The EIS modeling is applied to analyze the electrochemical characteristics. • The capacitive and pseudocapacitive characteristics of supercapacitors are analyzed. • Pseudocapacitance originates in the redox activity and specific adsorption of halide ions. A combination of two energy-stored modes, faradaic and electrostatic, has been applied to improve the energy density of supercapacitors with ionic liquid salt mixtures via impregnation of micro- and mesoporous carbon electrodes. An enhancement of capacitance was observed in the supercapacitors containing halide ion treated carbon electrodes, caused by the pseudocapacitive processes related to redox-active halide ions within and near the micro- and mesoporous carbon electrodes. To highlight the contribution of pseudocapacitance, an equivalent circuit model was applied to analyze the impedance spectra in detail. Significant pseudocapacitive behavior was only observed in the supercapacitors with halide ion treated carbon electrodes. A comparable result for both electrical double layer capacitance and pseudocapacitance values was obtained based on the direct current electrochemistry measurements as well as impedance fitting results. Meanwhile, according to the resistive behavior associated with the mass-transfer and faradaic processes, halide ion treated systems were more reactive compared with alkali ion treated systems. This article offers a brief and fundamental understanding with a focus on the contribution and distribution of both resistive and capacitive behavior analyzed by electrochemical impedance spectroscopy coupled with equivalent circuit modeling.

Experimental study on chemical structure and wetting influence of imidazole ionic liquids on coal

Three imidazole ionic liquid solutions were selected to handle coal with distinct degrees of metamorphism to research the influences of cation and anion ions in ionic liquids on functional groups and the relationship between functional groups and coal wettability. The chemical framework of coal was researched by FTIR and the wetting peculiarity of the coal was researched by contact angle meter. FTIR analysis showed that the cation and anion ions in ionic liquids significantly altered the framework of the coal. The contact angle measurement results demonstrated that compared with coal using pure water, the coal handled with ionic liquids showed a smaller contact angle. Finally, the relationship between contact angle and functional group content was analyzed. The results showed that the anions and cations of different ionic liquids can increase the content of hydrophilic groups in coal dust with different metamorphisms, such as OH···O, CO, and CO, and destroy the hydrophobic groups in the dissolved coal structure, such as CH2, CH and the benzene ring 3 substitutions. And 2 % [Emim][BF4] can effectively reduce the coal contact angle and improve the wettability of coal dust. The content of CO and OH···O groups had the greatest correlation with the contact angle, which were 0.845 and 0.754, respectively. By studying the influence of anions and cations in ionic liquids on the content of functional groups in coal, the effect of specific anions and cations on coal structure was further discovered, which provides a theoretical basis for the development of new ionic liquids with specific functions, and provides guiding significance for ionic liquid solutions to improve the wettability of coal and reduce the dust concentration.

Quantification of ionic-liquid ion source beam composition from time-of-flight data

Ionic-liquid ion sources produce beams of charged particles through evaporation and acceleration of ions and charged droplets from the surface of an ionic liquid. The composition of the emitted beam can impact the performance of ion sources for various applications such as focused beams for microfabrication and space propulsion. Numerical inference is considered for quantification of the beam composition of an ionic-liquid ion source through determining the current fraction of different species along with providing uncertainty in inferred values. An analysis of previously presented data demonstrates the ability to quantify the presence of ion clusters, including the distinct presence of heavy ion clusters such as heptamers. Quantification of beam composition will be an important technique for quantitative comparison of different time-of-flight data.

Negative ion beam bombardment of a protic ionic liquid: Alleviating surface charging and damage and analyzing the surface of organic insulating materials

Positive ion beams are widely used in surface processing and analysis; however, serious surface charging can occur in the case of insulating materials. To address this issue, we investigate bombardment effects of ionic liquid negative ions emitted from the tip of a sharp needle wetted with the protic ionic liquid, diethylmethylammonium trifluoromethanesulfonate. Experimental results show that the potential of an electrically floating metal target bombarded with the ionic liquid negative ions is slightly higher (about 1 V) than that of a front electrode, indicating that the target potential can be controlled by adjusting the potential of a nearby electrode. We also investigate the application of the negative ion bombardment in secondary ion mass spectrometry. Two types of insulating materials, polytetrafluoroethylene and polyethylene glycol, are analyzed. Experimental results show that the negative ion bombardment allows one to analyze organic insulating materials by adjusting sample bias potential, without charge neutralization such as electron flooding. Results obtained show that the ionic liquid negative ion beam is a useful tool for alleviating sample charging and damage because tens of negatively charged low-energy constituent atoms hit a surface locally and simultaneously. The ionic liquid negative ion bombardment is shown to have the advantages of both negative and polyatomic ion bombardment.

Experimental and simulation study on the capture and separation of CO2/CH4 by alkali metal complex ionic liquid

Solutions of [Bmim][BF4] ionic liquid (IL) mixed with three alkali metal tetrafluoroborate salts, i.e. LiBF4, NaBF4 and KBF4, were used to capture and separate CO2/CH4 at 303.15, 313.15 and 323.15 K under different pressures ranged from 500 to 3000 kPa. CO2 solubility in three alkali metal doped solutions decreases with the increase of temperature and decreasing pressure. High concentration of alkali metal salts does not show a very improvement for CO2 absorption, and even reduce CO2 capture instead in the presence of high concentration of LiBF4 in ionic liquid. Unexpectedly, KBF4 has the least solubility in [Bmim][BF4] and LiBF4 dissolved most in [Bmim][BF4] ionic liquid. On the contrary, the solubility of metal complex ionic liquids to CH4 decreased after adding alkali metal salts of any concentration. 0.01 mol·L−1 KBF4-IL showed the best CO2/CH4 solubility selectivity at 303.15 K, up to 54.5. On a basis of Quantum chemical calculations, binding energies between metal-doped ionic liquids and CO2/CH4 were calculated, following an order of KBF4-IL-CO2 > NaBF4-IL-CO2 > LiBF4-IL-CO2 and LiBF4-IL-CH4 > NaBF4-IL-CH4 > KBF4-IL-CH4, which is consistent with the experimental results. [BF4]− anions are approaching the metal ions and the larger metal cations, i.e. Na+ and K+, have longer distances with the anions than Li+, which explains the reason of reduced CO2 solubility when Li+ becomes more. Generally, high concentration of metal ions in ionic liquids are inferior for CO2 absorption because of the association of MBF4 with the ionic liquid. Therefore, the results of this paper can lay a theoretical foundation for CO2/CH4 capture separation.

Do certain imidazolium-based ionic liquid ion pairs/mordenite capture H2S by conformational traps? An ONIOM-DFT study

We present detailed ONIOM(ωB97X-D:PM6) calculations for the formation mechanism of novel composites combining protonic mordenites (H-MOR) with various ionic liquids: 1,3-dimethyl-imidazolium chloride [MMIm]Cl, 1-ethyl-3-methyl-imidazolium chloride [EMIm]Cl; 1-methyl-3-propyl-imidazolium chloride [PMIm]Cl; 1-butyl-3-methyl-imidazolium chloride [BMIm]Cl, 1-(2-hydroxyethyl)-3-methyl-imidazolium chloride [HEMIm]Cl, 1,3-dimethyl-1,3,2-diazasilolium chloride [MMSiN]Cl, and 1,3-dimethyl-1,3-diphospholium chloride [MMPP]Cl. The most feasible [M]-MOR formation mechanism ([M] + = [MMIm] + , [EMIm] + , [PMIm] + , [BMIm] + , [HEMIm] + , [MMSiN] + [MMPP] + ) involves an ion exchange at the T4O10 position favoring the isolation of a minimal number of [M] + isomers (i.e., conformational traps). The interaction of these [M]-MOR composites with pollutant gases has afterward been evaluated. Among the studied sytems, [EMIm]-MOR and [HEMIm]-MOR present electronic and steric conditions for potential applications in gas separation, capture, and storage (H 2 and H 2 S). The H-MOR framework exhibits two structural conformers with the [HEMIm] + cation in the confined space. Both, the MOR-T4O10-[HEMIm] and MOR-T4O10-[HEMIm] HB conformers, interconvert by a dynamic equilibrium with a transition state MOR-T4O10-TS1 acting as a conformational switch ( - ) that selectively recognizes and captures H 2 S through a plier-like conformation. • In silico design of novel composites combining Ionic Liquids with mordenite (MOR) was examined. • A composites formation mechanism that involves the ion exchange of H + by Imidazolium-based Ionic Liquid cation on T4O10 position in H-MOR. • The existence of conformational traps within the mordenite framework was demonstrated. • A new molecular H 2 S recognition/capture mechanism using [HEMIm]-MOR composite was proposed.

Dynamic Nonlinear Behavior of Ionic Liquid-Based Reservoir Computing Devices.

Herein, a physical reservoir device that uses faradaic currents generated by redox reactions of metal ions in ionic liquids was developed. Synthetic time-series data consisting of randomly arranged binary number sequences (“1” and “0”) were applied as isosceles-triangular voltage pulses with positive and negative voltage heights, respectively, and the effects of the faradaic current on short-term memory and parity-check task accuracies were verified. The current signal for the first half of the triangular voltage-pulse period, which contained a much higher faradaic current component compared to that of the second half of the triangular voltage-pulse period, enabled higher short-term memory task accuracy. Furthermore, when parity-check tasks were performed using a faradaic current generated by asymmetric triangular voltage-pulse levels of 1 and 0, the parity-check task accuracy was approximately eight times higher than that of the symmetric triangular voltage pulse in terms of the correlation coefficient between the output signal and target data. These results demonstrate the advantage of the faradaic current on both the short-term memory characteristics and nonlinear conversion capabilities and are expected to provide guidance for designing and controlling various physical reservoir devices that utilize electrochemical reactions.

(Digital Presentation) Reservoir Computing Device Using Faradaic Current of Electroactive Species in Ionic Liquids

Physical Reservoir Computing (PRC) has recently attracted significant attention as a computational method suitable for the edge AI computing, which requires both the high performance of information processing and energy conservative operation. There are two standard methods for evaluating PRC performance: the short-term memory (STM) task for the memory capacity and the parity check (PC) task for the nonlinear conversion capacity. We have developed PR device utilizing Faradaic currents generated by the redox reaction of metal ions in ionic liquids (ILs) and the impact of metal ions in ILs on the STM characteristics has been evaluated by comparing the RC device using metal-ion doped IL with that using non-doped (pure) IL [1]. In this study, we investigated the effect of Faradaic current on the STM and PC tasks by extracting the Faradaic current from the output signal when the triangular shaped input voltage pulse was applied to the PR device. It was found out that the peak shaped Faradaic current in the output signal improves not only the memory capacity but also the nonlinear conversion capability.A reservoir device with a transverse Pt/SiO2/Pt structure was prepared (Fig. 1) and solvated IL, Cu(Tf2N)2-Glyme(G3)=1:1 [2], was provided between the Pt electrodes as a reaction field where electrochemical reaction of Cu actively takes place. In order to prevent unnecessary copper deposition on the top surface of the Pt electrode, all areas other than the Pt electrode tip was covered with SiO2. As a result, a structure that allows deposition only between the terminals was realized. Furthermore, to prevent the migration of the IL by the application of an electric field, an IL pool surrounded by a resist wall was formed by patterning a spin-coated photoresist AZ5214E with a thickness of 2 µm. Au/Ti (100/10 nm) was deposited as the contact pad. The device characteristics were evaluated by cyclic voltammetry. In addition, a response of the device to the triangular pulses was investigated by using the B1530A WGFMU (waveform generator / fast measurement unit). STM and PC tasks were used to evaluate the time series data processing ability.In the present study, an artificial time-series data consisting of randomly connected binary data (0 and 1) was input to one of the Pt electrodes as the triangular shaped voltage pulse stream, while the other electrode was grounded. The positive and negative voltages were defined as 2bit data, ‘1’ and ‘0’, respectively. As shown in Fig. 2, triangular voltage pulse streams shown by the blue line were input to the reservoir device, and output current shown by red line was observed. Current peak appears when the polarity of the input signal is switched from positive to negative and vice versa (black arrow), but the peak intensity decreases when application of voltage pulses with the same polarity are continuously repeated. In addition, Cu deposition on the Pt electrode was observed. These results indicate that the origin of the peak is the Faradaic current generated by the electroactive species near the electrode. We divided output current data into two parts; the first half (yellow region), the latter half (green region). The first half corresponds to the rising part of the triangular pulse and involves the Faradaic current. On the other hand, the latter half corresponds to the descending part of the triangular pulse and is more featureless compared with the first half. We found that the accuracy of STM task was much higher when the first half was used. This tendency was also confirmed for the PC task. In PRC based on the concept of virtual nodes using a single physical device [3], the output signal complexity is considered to be related to the multidimensional transformation capability, which is one of indispensable property for PRC [4]. The present results suggest that the redox reaction of electroactive species in the IL increases the complexity of the output signal and improves the ability to extract time-series features.We thank Mr. Hiroshi Sato for supporting device fabrication processes. A part of this work was supported by "Nanotechnology Platform Program", Grant Number JPMXPF21NM0006.[1] D. Sato et al., MEMRISYS 2021, 4A-7 (2021).[2] H. Yamaoka et al., Chem. Lett., 46, 1832-1835 (2017).[3] L. Appeltant et al., Nat. Commun., 2, 468 (2011).[4] L. Appeltant et al., Sci. Rep., 4, 3629 (2014). Figure 1

Impact of molecular components on performance of multilayer graphene-based infrared emissivity modulator

Actively controlling the infrared emissivity of materials is critical for many applications, such as radiative cooling and thermal camouflage. Multilayer graphene (MLG) has shown great potential as a functional material with a tunable infrared emissivity. However, the spatial homogeneity in adjusting MLG's emissivity through ion intercalation is rather poor, which limits its practical applications. Here, we study how mixing various molecular components (e.g., ethanol) with ionic liquids affects the performance of MLG-based infrared emissivity modulators. The results indicate that introducing a moderate concentration of molecular components not only significantly improves spatial homogeneity in tuning emissivity but also enhances modulation depth, dynamic response, and the stability of the modulators. This is likely due to the increasing conductivity of the mixture and the improved wetting properties between the mixture and the separator, which leads to more effective charge transfer from ions in ionic liquids to carbons in graphene. The microscopic structure of MLG, revealed by Raman spectroscopy, confirms that the improvement in modulator performance is mostly due to homogeneous transportation of ions in the modulators. This not only sheds light on the underlying physics of the modulator but also greatly expands the options when selecting ionic liquids, thereby opening a new route for the modulator design.