Asymmetric Cation Research Articles

Air-Processed Efficient Cesium-Based Two-Dimensional Perovskite Solar Cells Based on Asymmetric Chiral Ammonium Salts.

Cesium-based two-dimensional (2D) perovskites with attractive phase and environmental stability have broad application prospects in single-junction and tandem perovskite solar cells (PSCs). However, the severe nonradiative recombination and significant energy losses due to disordered phase orientations and phase distributions greatly hinder the carrier transport performance of cesium-based 2D PSCs and severely limit their photovoltaic performance. Here, we employ an asymmetric chiral spacer cation source, (R)-α-phenylethylamine acrylate (R-α-PEAAA), to prepare high-quality 2D cesium-based films with uniform phase distribution and high out-of-plane orientation by air processing, resulting in efficient carrier transport. More importantly, the asymmetric chiral spacer R-α-PEA has a stronger dipole moment than its isomer (PEA), which can regulate the dielectric properties of cesium-based 2D perovskites and promote charge dissociation. In addition, the chiral R-α-PEA can optimize the morphology and out-of-plane orientation of perovskite films, reduce trap density and nonradiative recombination loss, and optimize energy level alignment, thus enhancing carrier transport. As a result, cesium-based 2D PSCs (R-α-PEA2Cs4Pb5I16, n = 5) achieved a record power conversion efficiency of 19.71% and the unencapsulated device maintained over 90% efficiency after 1500 h of continuous light exposure and ambient storage (35 ± 5% relative humidity). This study provides an idea for the development of chiral 2D perovskite with efficient charge carrier transport toward efficient and stable cesium-based 2D PSCs.

Synthesis and soft crystal structure-induced broad emission of (NH3C6H12NH3)InBr5·2H2O.

We report a simple synthesis of a new lead-free zero-dimensional (0D) hybrid halide compound, (5P1)InBr5·2H2O [(5P1) = NH3C6H12NH3], which hosts isolated and distorted octahedra of [InBr5(H2O)]2-, surrounded by bulky asymmetric organic cations [(5P1)2+] and H2O molecules. The hybrid crystals exhibit broad self trapped excitonic (STE) emission due to strong anharmonic soft structure.

Tailoring Perovskite Surface Potential and Chelation Advances Efficient Solar Cells.

Modifying perovskite surface using various organic ammonium halide cations has proven to be an effective approach for enhancing the overall performance of perovskite solar cells. Nevertheless, the impact of the structural symmetry of these ammonium halide cations on perovskite interface termination has remained uncertain. Here, this work investigates the influence of symmetry on the performance of the devices, using molecules based on symmetrical bis(2-chloroethyl)ammonium cation (B(CE)A+) and asymmetrical 2-chloroethylammonium cation (CEA+) as interface layers between the perovskite and hole transport layer. These results reveal that the symmetrical B(CE)A+ cations lead to a more homogeneous surface potential and more comprehensive chelation with uncoordinated Pb2+ compared to the asymmetrical cations, resulting in a more favorable energy band alignment and strengthened defect healing. This strategy, leveraging the spatial geometrical symmetry of the interface cations, promotes hole carrier extraction between functional layers and reduces nonradiative recombination on the perovskite surface. Consequently, perovskite solar cells processed with the symmetrical B(CE)A+ cations achieve a power conversion efficiency (PCE) of 25.60% and retain ≈91% of their initial PCE after 500 h of maximum power point operation. This work highlights the significant benefits of utilizing structurally symmetrical cations in promoting the performance and stability of perovskite solar cells.

Synchronous and zwitter-ion channels of (<i>R</i>)-5-methyl2-(1-methylethylidene)-cyclohexanone reaction with 4-phenyl-4<i>H</i>-1,2,4-triazoline-3,5-dione

The interaction of pulegone with enophil - 4-phenyl-4 H -1,2,4-triazoline-3,5-dione leads to the formation of two described earlier epimers: 1-[(1 R ,4 R )-4-methyl-1-(1-methylethenyl)-2-oxocyclohexyl]-4-phenyl-1,2,4-triazolidine-3,5-dione ( RR -isomer) and 1-[(1 S ,4 R )-4-methyl-1-(1-methylethenyl)-2-oxocyclohexyl]-4-phenyl-1,2,4-triazolidine-3,5-dione ( SR -isomer). Along with these epimers, we found another isomer - 1-{1-methyl-1-[(4 R )-4methyl-6-oxocyclohex-1-en-1-yl]ethyl}-4-phenyl-1,2,4-triazolidine-3,5-dione. Quantum chemical modeling has established that isomeric products of hydrogen substitution in pulegone by enophil are formed along three routes. In the SR -isomer formation route, the ene reaction proceeds consistently. The other two routes are implemented with the enophil approach from the R -side of the pulegon. These routes consist of two consecutive stages. At the first stage, an intermediate of the type of asymmetric cyclic aziridine cation is formed. Elimination of a proton from one of the geminal methyl groups of the intermediate leads to an RR -isomer with a terminal double bond. When a proton is eliminated from the methylene group of the pulegog ring, an internal unsaturated compound is formed. The ratio of the yield of the isomer with an internal double binding and the RR -isomer depends on the polarity of the aprotic solvents.

Regulating Phase Distribution of Dion-Jacobson Perovskite Colloidal Multiple Quantum Wells Toward Highly Stable Deep-Blue Emission.

Metal halide perovskite colloidal quantum wells (CQWs) hold great promise for modern photonics and optoelectronics. However, current studies focus on Ruddlesden-Popper (R-P) phase perovskite CQWs that contain bilayers of monovalent long-chain alkylamomoniums between the separated perovskite octahedra layers. The bilayers are packed back-to-back via weak van der Waals interaction, resulting in inferior charge carrier transport and easier decomposition of perovskite. This report first creates a new type of perovskite colloidal multiple QWs (CMQWs) in the form of Dion-Jacobson (D-J) structure by introducing an asymmetric diammonium cation. Furthermore, the phase distribution is optimized by the synergistic effect of valeric acid and zwitterionic lecithin, finally achieving pure deep-blue emission at 435nm with narrow full width at half maximum. The diammonium layer in D-J perovskite CMQWs features extremely short width of only ≈0.6nm, thereby contributing to more effective charge carrier transport and higher stability. Through the continuous photoluminescence (PL) measurement and corresponding theoretical calculation, the higher stability of D-J perovskite CMQWs than that of R-P structural CMQWs is confirmed. This work reveals the inherent superior stability of D-J structural CMQWs, which opens a new direction for fabricating stable perovskite optoelectronics.

A novel porous asymmetric cation exchange membrane with thin selective layer for efficient electrodialysis desalination

Ion exchange membranes (IEMs) are widely used in various electrochemical fields. Generally, identifying a solution for the trade-off between ion conductivity and dimensional stability is crucial for the further development of IEMs in the electrodialysis (ED) process. This study aimed to prepare a novel type of cation exchange membrane for electrodialysis desalination. Different from the previous cation exchange membranes with the thick and dense cross-section structure, the as-prepared asymmetric composite membranes in the present work composed of a thin and dense skin layer and a porous support layer via the pore-filling process of the skin layer of the porous poly (ether sulfone) (PES) membrane. Benefiting from such structural features, effective ion transport and dimensional stability were simultaneously achieved in the case of low ion exchange capacity. Ultimately, the optimal sulfonated poly (ether sulfone)-poly (ether sulfone) (SPES-PES) composite membrane simultaneously achieved ion transport enhancement, low swelling rate at 80 °C, and better mechanical stability compared to pure sulfonated poly (ether sulfone) (SPES) membranes. When applied to ED, the prepared 40 %SPES-PES membrane exhibited more excellent desalination performance (91.9%), higher current efficiency (127.5%), and lower energy loss (5.55 Kw·h·kg−1) compared to commercial membrane.

Ionic Liquids: Momentous Tools in Transdermal Delivery of Biomacromolecules

AbstractTransdermal drug delivery is a promising strategy characterized by minor fluctuations in blood concentrations, few adverse effects, convenience, and excellent patient compliance, especially for biomacromolecules. Conversely, traditional delivery methods are limited by their poor penetration abilities and complex preparation and application techniques. However, some inherent properties of biomacromolecules, such as large sizes, complex structure, and poor stability, can affect their ability to overcome skin barriers and reach deeper layers. Ionic liquids (ILs) are organic salts composed of asymmetric cations and anions in liquid form below 100 °C. ILs provide excellent protection for biomacromolecules and can facilitate their passage through the stratum corneum to cells for therapeutic effects. Therefore, they represent one of the most promising approaches to promoting transdermal penetration. Here, the barriers to effective transdermal delivery, including skin properties and the stability and biocompatibility of IL‐based biomacromolecule formulations, are highlighted and the current status of IL‐based biomacromolecule formulations are focused on, the tremendous advantages of using ILs based on current challenges in transdermal drug delivery are discussed, and light is shed on several ILs frequently used in the delivery of biomacromolecules.

Linking Molecular Structure and Lubrication Mechanisms in Tetraalkylammonium Orthoborate Ionic Liquids

While ionic liquids (ILs) have gained wide interest as potential alternative lubricants able to meet the requirements of next-generation tribological systems owing to their unique physico-chemical properties and promising lubricating behavior, our understanding of the mechanisms by which ILs reduce friction and/or wear is still elusive. Here, we combine macroscale tribological experiments with surface-analytical measurements to shed light on the lubrication mechanisms of a class of halogen-free ILs, namely tetraalkylammonium orthoborate ILs, at steel/steel sliding contacts. The tribological results indicate an improvement of the friction-reducing properties of these ILs as the length of the alkyl chains attached to ammonium cations increases. X-ray photoelectron spectroscopy analyses provide further evidence for the dependence of the lubrication mechanism of tetraalkylammonium orthoborate ILs on the IL structure. In the case of tetraalkylammonium orthoborate ILs with asymmetric ammonium cations containing a long alkyl chain, no sacrificial tribofilms were formed on steel surfaces, thus suggesting that the friction-reducing ability of these ILs originates from their propensity to undergo a pressure-induced morphological change at the sliding interface that leads to the generation of a lubricious, solid-like layered structure. Conversely, the higher friction response observed in tribological tests performed with tetraalkylammonium orthoborate ILs containing more symmetric ammonium cations and short alkyl chains is proposed to be due to the inability of this IL to create a transient interfacial layer owing to the reduced van der Waals interactions between the cationic alkyl chains. The resulting hard/hard contact between the sliding surfaces is proposed to lead to the cleavage of boron-oxygen bonds in the presence of water to form species that then adsorb onto the steel surface, including trivalent borate esters and oxalic acid from the decomposition of orthoborate anions, as well as tertiary amines from the degradation of alkylammonium cations induced by hydroxides released during the orthoborate decomposition reaction. The results of this work not only establish links between the molecular structure of a class of halogen-free ILs, their lubricating performance, and lubrication mechanism, but also provide evidence for the existence of multiple mechanisms underpinning the promising lubricating properties of ILs in general.

Room temperature ionic liquids with two symmetric ions.

Room temperature ionic liquids typically contain asymmetric organic cations. The asymmetry is thought to enhance disorder, thereby providing an entropic counter-balance to the strong, enthalpic, ionic interactions, and leading, therefore, to lower melting points. Unfortunately, the synthesis and purification of such asymmetric cations is typically more demanding. Here we introduce novel room temperature ionic liquids in which both cation and anion are formally symmetric. The chemical basis for this unprecedented behaviour is the incorporation of ether-containing side chains - which increase the configurational entropy - in the cation. Molecular dynamics simulations indicate that the ether-containing side chains transiently sample curled configurations. Our results contradict the long-standing paradigm that at least one asymmetric ion is required for ionic liquids to be molten at room temperature, and hence open up new and simpler design pathways for these remarkable materials.

Strain regulating mechanical stability and photoelectric properties of CH3NH3PbI3 containing the asymmetric CH3NH3 cations

Strain engineering effectively improves the intrinsic stability and power conversion efficiency (PCE) of organic-inorganic hybrid CH 3 NH 3 PbI 3 perovskite solar cells (PSCs), wherein the disordered state of asymmetric CH 3 NH 3 cations induces different photoelectric properties. However, there is limited information about the effect of asymmetric CH 3 NH 3 cations on structural evolution and mechanical stability under the strains ( ε ). Herein, the effect of strains on CH 3 NH 3 PbI 3 containing the asymmetric CH 3 NH 3 cations is investigated using density functional theory (DFT). The results show that the asymmetric CH 3 NH 3 cations have little impact on atomic structure at lower strains -4.0% < ε < 4.0%, contributing to stable mechanical property and linear regulation of photovoltaic properties. Under higher tensile strains ε > 4.0%, the differentiation of I-Pb bond length tends to be dominant in the fracture process of CH 3 NH 3 PbI 3 . The ultra-high compressive strains -15.0% < ε < -7.5% induce structural bending phase transition involving nonlinear changes of I-Pb bond length and Pb-I-Pb bond angle, which is strongly influenced by the asymmetry CH 3 NH 3 cations. The structural deformation on ab- plane with larger deformation resistance contributes greatly to bandgap regulation, attributing to overlapped (localized) charge density distribution of VBM I-5 p and Pb-6 s orbitals induced by shorter (longer) I-Pb bond length, resulting in the large shift of VBM. VBM upward bending caused by compression strains is favorable for the energy level match of PSCs. Viewed from anisotropic CH 3 NH 3 PbI 3 structure ( a = b < c ), the visible light absorption along c -axis direction obtains greater enhancement than the a -axis or b -axis direction. Moreover, the bandgap approximating Shockley-Queisser limits (1.34 eV) is obtained under compression strains -3.0% < ε < -2.0%, and thus enhancing the visible light absorption capacity. This work provides a detailed atomistic understanding of regulation mechanism on CH 3 NH 3 PbI 3 or other perovskites with similar electronic structures for improvement of PSCs. • The differentiation of I-Pb bond length tends to be dominant in fracture process of CH 3 NH 3 PbI 3 subjected to tensile strain. And bending phase transition is influenced strongly by the asymmetry CH 3 NH 3 cations under ultra-high compressive strains ε < -7.5%. • The compression strains of -2.0% < ε < -3.0% not only achieve the approximate optimal bandgap of Shockley-Queisser limits (about 1.34 eV) with favorable upward VBM/CBM band bending but also obtain stronger visible light absorption along c-axis.

Ionic liquid‐based materials for electrochemical biosensing

AbstractDue to their interesting features including negligible volatility, ease of designing in the construction, good chemical, and thermal stability, and excellent ionic conductivity, ionic liquids (ILs) have attracted a lot of attention to themselves in recent years. They are constructed from asymmetric anions and cations and are found in a liquid state lower than 100°C. Their unique features introduce them as candidates for the application in the structure of different types of electrochemical biosensors, in which they could act as electrolytes, or could be used as detecting agents. According to these features, this review aims to present an overview of the application of ILs in the structure of electrochemical sensors and biosensors. Based on this, after a brief description of the ILs and biosensors, the application of ILs in the structure of some of the recent electrochemical biosensors has been discussed and then, remarks and perspectives on these types of biosensors are explained.

Ionic liquids for electrochemical applications: Correlation between molecular structure and electrochemical stability window

Ionic gating has emerged as an effective and versatile tool to tune the charge-carrier density of a material and control its electronic ground state, as well as to develop low-temperature devices such as electrochemical transistors. Ionic liquids are a promising gating agent due to their high thermal- and electrochemical stability for both fundamental and applied research. However, the understanding of the correlation between the molecular structure of ionic liquids and their electrochemical stability is quite limited. For this reason, this study aims at determining the guidelines for synthesizing ionic liquids suitable for their use as electrolytes at low temperatures. A series of twenty-three ionic liquids having various ammonium cations, composed of three ''short chains'' and one ''long chain'', and Tf2N as the anion, were synthesized. Afterwards, their thermal behavior was determined to identify those ionic liquids exhibiting Tg < −50 °C. The anodic and cathodic limits of the selected ionic liquids were measured via linear-sweep voltammetry using an electrochemical transistor configuration, working at −33 °C. Electrochemical windows having absolute values from 2.9 to 5.7 V were measured. Overall, five guidelines were determined from the experimental results: first, the cations influence both cathodic and anodic limits; second, the asymmetric ammonium cations show larger electrochemical stability than symmetric ones; third, the electrochemical stability decreases at the increase of the length of the ''long chain''; fourth, alkyl long chains show a larger anodic limit, but smaller cathodic limit than ether long chains having the same length; fifth, the ether chain with largest electrochemical stability comprises three carbon atoms and one oxygen.

Conductivity prediction model for ionic liquids using machine learning.

Ionic liquids (ILs) are salts, composed of asymmetric cations and anions, typically existing as liquids at ambient temperatures. They have found widespread applications in energy storage devices, dye-sensitized solar cells, and sensors because of their high ionic conductivity and inherent thermal stability. However, measuring the conductivity of ILs by physical methods is time-consuming and expensive, whereas the use of computational screening and testing methods can be rapid and effective. In this study, we used experimentally measured and published data to construct a deep neural network capable of making rapid and accurate predictions of the conductivity of ILs. The neural network is trained on 406 unique and chemically diverse ILs. This model is one of the most chemically diverse conductivity prediction models to date and improves on previous studies that are constrained by the availability of data, the environmental conditions, or the IL base. Feature engineering techniques were employed to identify key chemo-structural characteristics that correlate positively or negatively with the ionic conductivity. These features are capable of being used as guidelines to design and synthesize new highly conductive ILs. This work shows the potential for machine-learning models to accelerate the rate of identification and testing of tailored, high-conductivity ILs.

Ammonium enables reversible aqueous Zn battery chemistries by tailoring the interphase

<h2>Summary</h2> Aqueous rechargeable Zn metal batteries (RZMBs) are promising candidates for coupling with intermittent renewable energy sources to realize a carbon-neutral energy transition. However, irreversible issues of Zn metal anodes and a poor understanding of the interphasial chemistry severely limit the viability of RZMBs. Here, we demonstrate that the addition of an asymmetric alkylammonium cation, trimethylethyl ammonium-bis(trifluoromethylsulfonyl)imide (Me₃EtN-TFSI), as a supporting salt into a traditional aqueous electrolyte results in improved Zn anode reversibility. Performance improvements are attributed to the formation of interphasial chemistries including ZnF₂, ZnCO₃, and fluoro-polymeric species, especially when combined with CO_2. By tailoring the Zn interphase, this electrolyte exhibited excellent stability in Na₂V₆O₁₆ · 1.63H₂O (HNVO)/Zn full cells, with a high specific capacity sustained (>100 mAh g⁻¹) over 1,000 cycles at 300 mA g⁻¹. A combination of experiments and modeling showed the importance of tuning interphases to further improve Zn reversibility and RZMBs.

Two-dimensional lamellar MXene/three-dimensional network bacterial nanocellulose nanofiber composite Janus membranes as nanofluidic osmotic power generators

In the field of nanofluidic osmotic power generators, it has been an ultimate but seemingly distant goal to controllably fabricate the different-dimensional confined space including slits, network, nanochannels or their composition to control the ion transport. We demonstrated ion transport behaviors through ultimately 2D lamellar MXene/3D network bacterial nanocellulose nanofiber composite Janus membranes under the different transmembrane concentration gradient. The heterogeneous multilayers Janus membrane comprised effectively stacked hydrophobic MXene to hydrophilic bacterial nanocellulose (BNC). The asymmetric cations transport phenomena were explained in terms of asymmetric surface charges polarization in the confined space. Our results provided a facile and general strategy for studying the effects of membrane-scale confinement, which was important for the development of biomimetic energy conversion, ionic seizing, chemical sensing and other nanoscale technologies.

Structure, Stability, and Photocatalytic Activity of a Layered Perovskite Niobate after Flux-Mediated Sn(II) Exchange.

A new strategy to incorporate the Sn(II) cation and its stereoactive lone pair into the structure of a photocatalytic oxide has been achieved by leveraging the asymmetric coordination environments within the (111)-oriented perovskite-type layers of Ba5Nb4O15. This layered perovskite represents one of the few known photocatalysts capable of efficiently splitting water, but its activity is restricted to ultraviolet radiation owing to its large band gap. By reacting this layered niobate at 350 °C for 24 h within a low-melting SnCl2/SnF2 salt, the new (Ba1-xSnx)Nb4O15 (x = 0-0.5; P3̅m1; a = 5.79650(5) Å, c = 11.79288(8) Å; Z = 2) has been prepared in high purity with up to ∼50% Sn(II) cations. Statistical disordering of the Sn(II) cations was probed by neutron diffraction Rietveld refinements and found to occur predominantly over the asymmetric cation sites, Ba2 and Ba3, for the 40% Sn(II) composition of x = 0.4. An increasing Sn(II) amount significantly red-shifts the band gap (Eg) from 0% Sn for x = 0 (3.78 eV; ultraviolet, indirect) to 40% Sn for x = 0.4 (Eg = 2.35 eV; visible, indirect), as found by UV-vis diffuse reflectance. Density functional theory calculations show an increasing metastability, i.e., a thermodynamic instability toward decomposition to the simpler oxides SnO, Nb2O5, and SnNb2O6. A synthetic limit of ∼50% Sn(II) cations can be kinetically stabilized under these reaction conditions. For the highest Sn(II) amounts, photocatalytic rates are observed for the production of molecular oxygen from water of up to ∼77 μmol O2 h-1 g-1 (visible irradiation) and ∼159 μmol O2 h-1 g-1 (UV-vis irradiation), with apparent quantum yields of ∼0.35 and 0.52%, respectively. By comparison, pure Ba5Nb4O15 exhibits no measurable photocatalytic activity under visible-light irradiation. Electronic structure calculations show that the decreased band gap stems from the introduction of the Sn(II) cations and the formation of a higher-energy valence band arising from the filled 5s2 valence orbitals. Thus, visible-light bandgap excitation occurs from electronic transitions predominantly involving the Sn(II) (5s2) to Nb(V) (4d0) cations. This study demonstrates the new and powerful utility of low-temperature Sn(II)-exchange reactions to sensitize layer-type oxide photocatalysts to the visible region of the solar spectrum, which is facilitated by exploiting their asymmetric cation environments.

Strain Regulating Mechanical Stability and Photoelectric Properties of Ch3nh3pbi3 Containing the Asymmetric Ch3nh3 Cations

Strain Regulating Mechanical Stability and Photoelectric Properties of Ch3nh3pbi3 Containing the Asymmetric Ch3nh3 Cations

Symmetry breaking of A3M2X9-type perovskite derivatives induced by polar quaternary ammonium cations: achieving efficient nonlinear optical properties.

Low-dimensional organic-inorganic metal halides, especially lead-free perovskites, are attracting increasing attention because of their environmentally friendly processing, flexible structures, chemical stability, and promising nonlinear optical properties. Herein, we report a new stable polar 0D lead-free hybrid bismuth chloride to enable the second-harmonic generation (SHG) active material (BTA)3Bi2Cl9 (BTA = benzyltriethylammonium, C6H5CH2N(C2H5)3+) that was obtained by the antisolvent vapor diffusion method and crystallized in the polar Cc space group. Its structure features organic cations surrounded by face-sharing [Bi2Cl9]3- dimers. (BTA)3Bi2Cl9 exhibits a wide direct bandgap (3.21 eV) and a strong phase-matchable SHG conversion efficiency (1.39 × KDP). Theoretical calculation reveals that the SHG response is owing to the synergistic effect of distorted inorganic [Bi2Cl9]3- anions and polar organic BTA+ cations. This work not only enriches the family of organic-inorganic A3M2X9 (A = monovalent cations; M = trivalent metal ions; and X = halide ions) NLO crystals but also provides the possibilities for further designing novel lead-free semiconducting piezoelectric, pyroelectric and ferroelectric materials.

Spectral Stable Blue-Light-Emitting Diodes via Asymmetric Organic Diamine Based Dion-Jacobson Perovskites.

The spectral instability issue is a challenge in blue perovskite light-emitting diodes (PeLEDs). Dion–Jacobson (DJ) phase perovskites are promising alternatives to achieve high-quality blue PeLEDs. However, the current exploration of DJ phase perovskites is focused on symmetric divalent cations, and the corresponding efficiency of blue PeLEDs is still inferior to that of green and red ones. In this work, we report a new type of DJ phase CsPb(Br/Cl)3 perovskite via introduction of an asymmetric molecular configuration as the organic spacer cation in perovskites. The primary and tertiary ammonium groups on the asymmetric cations bridge with the lead halide octahedra forming the DJ phase structures. Stable photoluminescence spectra were demonstrated in perovskite films owing to the suppressed halide segregation. Meanwhile, the radiative recombination efficiency of charges is improved significantly as a result of the confinement effects and passivation of charge traps. Finally, we achieved an external quantum efficiency of 2.65% in blue PeLEDs with stable spectra emission under applied bias voltages. To our best knowledge, this is the first report of asymmetric cations used in PeLEDs, which provides a facile solution to the halide segregation issue in PeLEDs.

Synthesis and Characterization of a Novel Hydroquinone Sulfonate-Based Redox Active Ionic Liquid.

Introducing redox-active moieties into an ionic liquid (IL) structure is an exciting and attractive approach that has received increasing interest over recent years for a various range of energy applications. The so-called redox-active ionic liquids (RAILs) provide a highly versatile platform to potentially create multifunctional electroactive materials. Ionic liquids are molten salts consisting of ionic species, often having a melting point lower than 100 °C. Such liquids are obtained by combining a bulky asymmetric organic cation and a small anion. Here, we report on the synthesis of a novel RAIL, namely 1-butyl-3-methylimidazolium hydroquinone sulfonate ((BMIM)(HQS)). (BMIM)(HQS) was synthesized in a two-step procedure, starting by the quaternization of methylimidazole using butylchloride to produce 1-butyl-3-methylimidazolium chloride ((BMIM)(Cl)), and followed by the anion exchange reaction, where the chloride anion is exchanged with hydroquinone sulfonate. The resulting product was characterized by 1H NMR, 13C NMR, FT-IR spectroscopy, themogravimetric analysis, and differential scanning calorimetry, and shows a high stability up to 340 °C. Its electrochemical behavior was investigated using cyclic voltammetry at different temperatures and its viscosity analysis was also performed at variable temperatures. The electrochemical response of the presented RAIL was found to be temperature dependent and diffusion controlled. Overall, our results demonstrated that (BMIM)(mix of HQS and HSQ) is redox active and possesses high stability and low volatility, leading to the employment of this RAIL without any additional supporting electrolyte or additives.