Room Temperature Ionic Liquids Research Articles

Reactivity Manipulation of Ionic Liquid Based on Alkyl Primary Ammonium: Protonation Control Using 4‐tert‐Butylpyridine Additive for Effective Spontaneous Passivation of Perovskite via Hole Transport Material Deposition

Alkyl‐primary‐ammonium‐based room‐temperature ionic liquids (RTILs) designed to exhibit specific reactivities allowing functions that cannot be achieved by other RTILs have recently emerged. The archetype of the reactive RTILs is n‐octylammonium bis(trifluoromethanesulfonyl)imide (OA‐TFSI), which has promising functions as an additive for hole transport materials (HTMs) in perovskite solar cells (PSCs); the high reactivity of the OA cations on the perovskite surface allows spontaneous perovskite passivation via HTM deposition, effectively improving the photovoltaic (PV) performance. However, although the reactivity manipulation of the reactive RTILs is instrumental for exploiting their potential functions and exploring their application scope, methods for reactivity control have not been developed. Herein, it is proposed that the coaddition of a pyridine derivative (4‐tert‐butylpridine: TBP) can effectively manipulate the reactivity of OA‐TFSI by controlling the protonation between OA and the 2,2′,7,7′‐tetrakis‐(N,N‐di‐4‐methoxyphenylamino)‐9,9′‐spirobifluorene (Spiro‐OMeTAD) HTM. The TBP prevents OA deprotonation presumably via stabilization of the OA cation, thus retaining its ammonium form, which allows efficient spontaneous perovskite passivation, effectively enhancing the PV performance. This reveals the protonation preference in the OA‐TFSI system, which is opposite to that in conventional RTILs. This first proposal of a method in manipulating reactivity of the reactive RTILs will contribute to the development of materials science.

Understanding the Decamethylferrocene FeIII/IV Oxidation Process in Tris(pentafluoroethyl)trifluorophosphate-Containing Ionic Liquids at Glassy Carbon and Boron-Doped Diamond Electrodes.

Under voltammetric conditions, the neutral decamethylferrocene ([Me10Fc]) to cationic ([Me10Fc]+) FeII/III process is a well-known reversible outer-sphere reaction. A companion cationic [Me10Fc]+ to dicationic [Me10Fc]2+ FeIII/IV process has been reported under direct current (DC) cyclic voltammetric conditions at highly positive potentials in liquid SO2 at low temperatures and in a 1.5:1.0 AlCl3/1-butylpyridinium chloride melt. This study demonstrates that in room-temperature ionic liquids containing the hard to oxidize and hydrophobic tris(pentafluoroethyl)trifluorophosphate anion, the [Me10Fc]+/2+ process can be detected as a quasi-reversible reaction at glassy carbon (GC) and boron-doped diamond (BDD) electrodes. Large amplitude Fourier-transformed alternating current (FT-AC) voltammetry minimizes background current contributions occurring at potentials similar to those of the FeIII/IV process in the second and higher-order harmonics. This enables a straightforward determination of the thermodynamics and kinetics for both the FeII/III and FeIII/IV processes. Unlike the ideal outer-sphere FeII/III process, the parameters of the FeIII/IV process may be impacted by ion-interaction effects. For the faster FeII/III process, heterogeneous rate constants are approximately 10 times smaller at BDD than those at GC electrodes. This electrode dependence is less pronounced for the slower FeIII/IV process. The slower BDD kinetics may be attributed in part to a density of states lower than that at GC.

Two Fold Amplification of Paste Electrode with Pt/Graphene Nanocomposite and Room Temperature Ionic Liquid to Monitoring of Vitamin B6 in Environmental and Food Samples

Two Fold Amplification of Paste Electrode with Pt/Graphene Nanocomposite and Room Temperature Ionic Liquid to Monitoring of Vitamin B6 in Environmental and Food Samples

Boosting degradation of C4mim cation by metal alkoxide-derived Co4S3-activated Oxone: Yolk-Shell-Engineered enhancement and DFT-assisted toxic evaluation

The low bio-degradability of room-temperature ionic liquids (RTILs) makes RTILs a new class of persistent contaminants. It is urgent to develop useful technology to eliminate RTILs to prevent their presence in the environment. Sulfate-radical advanced oxidation processes (SR-AOPs) are particularly suitable for degrading such low-biodegradability pollutants. This study introduces a novel SR-AOP aimed at eliminating the representative RTIL, 1-butyl-3-methylimidazolium chloride (C4M), using an enhanced catalyst to activate Oxone. Traditionally, cobalt (Co) has been used for Oxone activation, but homogeneous catalysis with Co ions poses recovery challenges and secondary pollution risks. Recent studies suggest that cobalt sulfides (CSs) are more promising due to their superior redox properties, which are critical for effective Oxone activation. In this work, we developed a catalyst composed of cobalt sulfide (CS) with a unique yolk-shell (YS) structure, termed YSCS, to maximize catalytic activity. YSCS was easily fabricated from Co-Glycerate (CoG) precursors through a self-destruction/reconstruction process during sulfidization, resulting in a YS structure covered by self-assembled Co4S3 nanoplates. This morphology provides a highly mesoporous structure, enhanced electrochemical properties, and expanded active sites. Consequently, YSCS demonstrated significantly higher catalytic activity for Oxone activation compared to its precursor CoG and the benchmark Co3O4, with a reaction rate constant (k) of 0.108 min-1, surpassing those of Co3O4 NP + Oxone (0.007 min-1) and CoG + Oxone (0.023 min-1). Additionally, YSCS + Oxone exhibited a lower activation energy (Ea) of 17.8 kJ/mol for C4M degradation. The degradation pathway of C4M by YSCS + Oxone was thoroughly investigated using Fukui indices and analyzing the degradation by-products. Toxicity assessments showed that YSCS + Oxone significantly reduces the acute toxicity and bioconcentration factor of C4M, as well as potential mutagenicity and developmental toxicity risks. These findings confirm that YSCS is a highly effective catalyst for Oxone activation and RTIL degradation in water.

Electrochemical instability of room-temperature ionic liquids with LiTFSI at elevated temperature and its consequences in Li/Li-ion based half-cells and full-cells

High-temperature Li-ion batteries capable of operating up to 100 ℃ can replace lithium thionyl chloride primary batteries in specialized industrial applications. Room-temperature ionic liquids (RTIL) offer high thermal stability and can be a promising choice of electrolyte for high-temperature batteries. This work elucidates that high thermal stability alone does not guarantee effective battery operation due to the electrochemical instability observed in RTIL-LiTFSI mixtures at elevated temperatures. Here, we investigate the impact of varying electrochemical stability in RTILs on half-cell, full-cell, and calendar aging. Electrochemical instability of the electrolyte at the cathode interface injects additional electrons and Li-ions into the electrochemical cell, triggering a cascade of detrimental chain reactions that hinder efficient battery performance. We demonstrate that electrochemical information gathered from a full-cell configuration can frequently obscure the presence of electrochemical instability at the cathode surface. To accurately evaluate this instability, it is essential to perform in-depth half-cell studies and other characterizations. Our results indicate that cathode electrolyte interphase (CEI) can reach a thickness of up to 100 nm, with a depth-dependent composition showing higher concentration of inorganic species like LiF and LiNSO near the cathode surface. Further, accelerated calendar aging measurements of such cells at high temperature revealed complete irreversible self-discharge within as little as 14 days. These findings shed light on the critical factors influencing the stability and performance of cells under challenging operating conditions.

Digital light processing 3D printing of polymerizable ionic liquids towards carbon capture applications

This study presents new 3D printable materials based on ad-hoc synthesized photocurable imidazolium ionic liquids (ILs) with bis(trifluoromethanesulfonyl)imide (NTf2)− as counterion and two different alkyl chain's structures at the cation, with enhanced CO2 capture properties. The molecular structure of the synthesized ILs was confirmed through NMR technique and a polymerization study was carried out, by means of photorheological tests and FT-IR analyses, on formulations containing a crosslinking monomer (PEGDA). The study confirmed the good reactivity of the formulations that makes them suitable for digital light processing (DLP) 3D printing technique. Simple membranes were then tested through high pressure CO2 uptake analysis to estimate their capture efficiency, comparing the results with the standard room temperature ionic liquid (RTIL) counterpart, and evidencing an increase of CO2 absorption regardless the pressure applied. At last, complex gyroid-like structures incorporating the synthesized ILs were successfully 3D printed, showing the remarkable ability of these materials to be processed with 3D printing technology while maintaining the great CO2 capture performances of ionic liquids. This preliminary work paves the way for the implementation of “ad-hoc” designs to create filters or devices to enhance the CO2 capture.

Redox potentials in ionic liquids: Anomalous behavior?

Redox potentials depend on the nature of the solvent/electrolyte through the solvation energies of the ionic solute species. For concentrated electrolytes, ion solvation may deviate significantly from the Born model predictions due to ion pairing and correlation effects. Recently, Ghorai and Matyushov [J. Phys. Chem. B 124, 3754-3769 (2020)] predicted, on the basis of linear response theory, an anomalous trend in the solvation energies of room temperature ionic liquids, with deviations of hundreds of kJ/mol from the Born model for certain size solutes/ions. In this work, we computationally evaluate ionic solvation energies in the prototypical ionic liquid, 1-butyl-3-methylimidazolium tetrafluoroborate (BMIM/BF4), to further explore this behavior and benchmark several of the approximations utilized in the solvation energy predictions. For comparison, we additionally compute solvation energies within acetonitrile and molten NaCl salt to illustrate the limiting behavior of purely dipolar and ionic solvents. We find that the overscreening effect, which results from the inherent charge oscillations of the ionic liquid, is substantially reduced in magnitude due to screening from the dipoles of the molecular ions. Therefore, for the molten NaCl salt, for which the ions do not have permanent dipoles, modulation of ionic solvation energies from the overscreening effect is most significant. The conclusion is that ionic liquids do indeed exhibit unique solvation behavior due to peak(s) in the electrical susceptibility caused by the ion shell structure; redox potential shifts for BMIM/BF4 are of more modest order ∼0.1V, but may be larger for other ionic liquids that approach molten salt behavior.

Ionic Liquid Crystal-Polymer Composite Electromechanical Actuators: Design of Two-Dimensional Molecular Assemblies for Efficient Ion Transport and Effect of Electrodes on Actuator Performance.

We present the development of free-standing ionic liquid crystal-polymer composite electrolyte films aimed at achieving high-frequency response electromechanical actuators. Our approach entails designing novel layered ionic liquid-crystalline (LC) assemblies by complexing a mesomorphic dimethylphosphate with either a lithium salt or a room-temperature ionic liquid through the formation of ion-dipole interactions or hydrogen bonds. These electrolytes, exhibiting room-temperature ionic conductivities on the order of 10-4 S cm-1 and wide LC temperature ranges up to 77 °C, were successfully integrated into porous polymer networks. We systematically investigated the impact of ions and electrodes on the performance of ionic electroactive actuators. Specifically, the Li+-based liquid crystal-polymer composite actuator with PEDOT:PSS electrodes demonstrated the highest bending deformation, achieving a strain of 0.68% and exhibiting a broad frequency response up to 110 Hz, with a peak-to-peak displacement of 3 μm. In contrast, the ionic-liquid-based liquid crystal-polymer composite actuator with active carbon electrodes showcased a bending response at a maximum frequency of 50 Hz and a force generation of 0.48 mN, without exhibiting the back relaxation phenomenon. These findings offer valuable insights for advancing high-performance electromechanical systems with applications ranging from soft robotics to haptic interfaces.

Effect of charge on the rotation of prolate nitroxide spin probes in room-temperature ionic liquids

We have studied the rotational diffusion of two prolate nitroxide probes, the doubly negatively charged peroxylamine disulfonate (Frémy's salt − FS) and neutral di-tert-butyl nitroxide (DTBN), in a series of 1-alkyl-3-methylimidazolium tetrafluoroborate room-temperature ionic liquids (RTILs) having alkyl chain lengths from two to eight carbons using electron paramagnetic resonance (EPR) spectroscopy. Though the size and shape of the probes are reasonably similar, they behave differently due to the charge difference. The rotation of FS is anisotropic, and the rotational anisotropy increases with the alkyl chain length of the cation, while the rotation of DTBN is isotropic. The hyperfine coupling constant of DTBN decreases as a function of the alkyl chain length and is proportional to the relative permittivity of ionic liquids. On the other hand, the hyperfine coupling constant of FS increases with increasing chain length. These behaviors indicate the location of each probe in RTILs. FS is likely located in the polar region near the network of charged imidazolium ions. DTBN molecules are predominately distributed in the nonpolar domains.

Activation Energy of Ion Desorption at Ionic Liquid/Pt Electrode Interfaces: A Sum-Frequency Generation Vibrational Spectroscopic Study.

Electrolyte/electrode interfaces of room-temperature ionic liquids (RTILs) exhibit hysteretic responses to different applied potentials owing to the differences in the ion adsorption/desorption processes; the ion desorption requires excess potential, which reflects the activation energy of ion desorption. Thus far, the contributions of the ion adsorption energy and the activation barrier for ion desorption toward the ion-dependent excess potential have not been quantified. Herein, we report on our infrared-visible sum-frequency generation vibrational spectroscopy study of the hysteretic responses of the anion adsorption/desorption at Pt electrode interfaces using neat, binary, and diluted RTILs composed of 1-butyl-3-methylimidazolium cations ([C4mim]+) and bis(trifluoromethanesulfonyl)amide ([TFSA]-) and trifluoromethanesulfonate ([OTf]-) anions. Experimental results are compared to the theoretical calculations for the electric double layer model. The hysteretic response of the RTIL/Pt interface derives predominantly from the activation energy of anion desorption, which causes the negative excess potential required for anion desorption. A comparison of the anion adsorption/desorption behaviors of neat RTILs with those of binary and diluted RTILs reveals that the large activation energy of anion desorption at the neat RTIL/Pt interface originates largely from the activation barrier for restructuring ionic layering in the diffuse layer.

Tunable liquid lens for three-photon excitation microscopy

We demonstrate a novel electrowetting liquid combination using a room temperature ionic liquid (RTIL) and a nonpolar liquid, 1-phenyl-1-cyclohexene (PCH) suitable for focus-tunable 3-photon microscopy. We show that both liquids have over 90% transmission at 1300 nm over a 1.1 mm pathlength and an index of refraction contrast of 0.123. A lens using these liquids can be tuned from a contact angle of 133 to 48° with applied voltages of 0 and 60 V, respectively. Finally, a three-photon imaging system including an RTIL electrowetting lens was used to image a mouse brain slice. Axial scans taken with an electrowetting lens show excellent agreement with images acquired using a mechanically scanned objective.

Speciation of uranium bis(trifluoromethylsulfonyl)imide in a room temperature ionic liquid

Speciation of uranium bis(trifluoromethylsulfonyl)imide in a room temperature ionic liquid

Effects of Water Content on the Transport and Thermodynamic Properties of Phosphonium Ionic Liquids.

We present a numerical investigation of the influence of water content on the dynamic properties of a family of phosphonium-based room-temperature ionic liquids. The study presents a compelling correlation between structural changes in water-ionic liquid solutions and thermodynamic and transport properties across diverse systems. The results for phosphonium ionic liquids are compared with 1-butyl-3-methylimidazolium hexaphosphate ([bmim]PF6) as a reference. Through this approach, phosphonium cation structure-related characteristics can be identified and placed within the broader context of ionic liquids. These insights are underpinned by observed changes in interaction energy, boiling point, diffusion rate, and viscosity, highlighting the crucial role of water molecules in weakening the strength of interactions between ions within the ionic liquid. The investigation also explains temperature-dependent trends in phosphonium cations, showing that alkyl group length and molecular symmetry are important tuning parameters for the strength of Coulomb interactions. These results contribute to a refined understanding of phosphonium ionic liquid behavior in the presence of water, offering valuable insights for optimizing their use in diverse fields.

Alkyl-π Functional Molecular Gels: Control of Elastic Modulus and Improvement of Electret Performance.

The development of optoelectronically-active soft materials is drawing attention to the application of soft electronics. A room-temperature solvent-free liquid obtained by modifying a π-conjugated moiety with flexible yet bulky alkyl chains is a promising functional soft material. Tuning the elastic modulus (G') is essential for employing optoelectronically-active alkyl-π liquids in deformable devices. However, the range of G' achieved through the molecular design of alkyl-π liquids is limited. We report herein a method for controlling G' of alkyl-π liquids by gelation. Adding 1 wt % low-molecular-weight gelator formed the alkyl-π functional molecular gel (FMG) and increased G' of alkyl-π liquids by up to seven orders of magnitude while retaining the optical properties. Because alkyl-π FMGs have functional π-moieties in the gel medium, this new class of gels has a much higher content of π-moieties of up to 59 wt % compared to conventional π-gels of only a few wt %. More importantly, the gel state has a 23 % higher charge-retention capacity than the liquid, providing better performance in deformable mechanoelectric generator-electret devices. The strategy used in this study is a novel approach for developing next-generation optoelectronically-active FMG materials.

Liquid metal manifold microchannel heat sink for ultra-high heat flux cooling

Advanced heat dissipation technology is crucial for chip operation and performance utilization. Room temperature liquid metal convection cooling technology has demonstrated its efficacy as a viable approach for addressing high heat flux heat dissipation. However, the smaller specific heat capacity of liquid metal leads to a large temperature rise, hindering the advancement of its cooling technology. To address this, a liquid metal manifold channel structure is proposed to convert the continuous long-range flow into a segmented short-range flow. The good matching between liquid metal and manifold structures is adequately demonstrated through a comparison with alternative coolant and channel structure. The simulation results demonstrate the effectiveness of liquid metal manifold channel cooling in dealing with a heat flux of 1000 W/cm2, ensuring that the maximum temperature of the chip remains below 351.7 K. Moreover, the convective heat transfer coefficient even reaches 106 W/(m2·K), which is ten times larger than that of water conventional microchannel heat sink. Orthogonal experiments analyzed the impact of structural parameters on dissipation performance, including the height of the microchannel, ratio of manifold length to fin length, length of fin in manifold, width of channel, and ratio of fin with to channel width. The height of the microchannel has been identified as the most critical factor. This manifold structure mitigates the inherent limitation of liquid metal's lower specific heat capacity, enabling efficient thermal management for electronic devices under ultra-high heat flux conditions.

Green Synthesis of a Molecularly Imprinted Polymer Based on a Novel Thiophene-Derivative for Electrochemical Sensing.

An environmentally friendly and sustainable approach was adopted to produce a molecularly imprinted polymer (MIP) via electropolymerization, with remarkable electrochemical sensing properties, tested in tyrosine (tyr) detection. The 2,2'-bis(2,2'-bithiophene-5-yl)-3,3'-bithianaphtene (BT2-T4) was chosen as functional monomer and MIP electrosynthesis was carried out via cyclic voltammetry on low-volume (20 μL) screen-printed carbon electrodes (C-SPE) in ionic liquid 1-butyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide ((BMIM) TFSI). An easy and rapid washing treatment allowed us to obtain the resulting MIP film, directly used for tyr electrochemical detection, carried out amperometrically. The sensor showed a linear response in the concentration range of 15-200 μM, with LOD of 1.04 µM, LOQ of 3.17 μM and good performance in selectivity, stability, and reproducibility. Tyrosine amperometric detection was also carried out in human plasma, resulting in a satisfactory recovery estimation. The work represents the first use of BT2-T4 as a functional monomer for the production of a molecularly imprinted polymer, with a green approach afforded by using a few microliters of a room temperature ionic liquid as an alternative to common organic solvents on screen-printed carbon electrodes, resulting in a valuable system that meets the green chemistry guidelines, which is today an essential criterion in both research and application field.

Physicochemical Properties of Pyrrolidinium-based Room Temperature Ionic Liquids with Propoxyethyl, Ethoxypropyl, or (Methoxymethoxy)ethyl Group

Physicochemical Properties of Pyrrolidinium-based Room Temperature Ionic Liquids with Propoxyethyl, Ethoxypropyl, or (Methoxymethoxy)ethyl Group

Using Deep Eutectic Solvent-Assisted Plating Baths to Electrodeposit Composite Coatings: A Review

This review provides a systematic analysis of the literature data on the electrodeposition of composite coatings using plating baths based on a new generation of room-temperature ionic liquids known as deep eutectic solvents (DESs). Such systems offer several advantages over traditionally used aqueous electrolytes and organic solvent-based electrolytes. The colloidal–chemical properties of suspension and colloidal electrolytes for composite deposition are thoroughly examined. New theories describing the kinetics of the co-deposition of composite layers are characterized. The kinetics and mechanisms of electrochemical deposition processes of composite coatings with metallic matrices are discussed. Case studies regarding the electrodeposition of composite coatings based on electrodeposited copper, silver, zinc, tin, nickel, cobalt, and chromium from DES-assisted electroplating baths are described and systematized. The main prospective directions for further research in the discussed scientific area are highlighted.

Atomically precise Pdm(SR)n nanoclusters for efficient hydrogen evolution reaction

Thiolate (SR) protected noble metal nanoclusters have grasped immense attention because of their promising applications in electrocatalysis, electrochemical sensors, photoluminescencse, supercapacitor and energy production. Among the noble metals, numerous reports have highlighted interesting results for Au25(SR)18, Au22(SR)18 and Ag44(SR)30 clusters but Pd and Pt nanoclusters are less addressed. Room temperature ionic liquids (RTIL) show enhanced electrocatalytic activity and stability as a binding matrix as compared to commercial binders like Nafion, Polyvinylidene fluoride (PVDF) and so on. Here, we have synthesised water-soluble thiolate 3-mercaptopropyl sulfonate (MPS) capped Palladium nanoclusters (Pd-MPS NCs). Further, Poly Acrylamide Gel Electrophoresis (PAGE), a separation technique was used to isolate size-dependent NCs and their electrocatalytic activity for the hydrogen evolution reaction (HER) with room temperature ionic liquid as a binding matrix was demonstrated. The electron microscope images of isolated Pd-MPS NCs from these three bands (obtained from PAGE separation) resulted with size ranges of 0.8-1.8 nm, 2-4 nm and 4.2-8 nm respectively. Among the three bands obtained from PAGE gel from the crude Pd NCs, the ultrasmall Pdm(SR)n NCs was isolated from the lower band resulted in high HER activity with less overpotential of 197 mV and a Tafel slope of 125.2 mV dec-1 as compared to Pd-MPS NCs obtained from the other two distinctive bands.

Room Temperature Ionic Liquid Capping Layer for High Efficiency FAPbI3 Perovskite Solar Cells with Long-Term Stability.

Ionic liquid salts (ILs) are generally recognized as additives in perovskite precursor solutions to enhance the efficiency and stability of solar cells. However, the success of ILs incorporation as additives is highly dependent on the precursor formulation and perovskite crystallization process, posing challenges for industrial-scale implementation. In this study, a room-temperature spin-coated IL, n-butylamine acetate (BAAc), is identified as an ideal passivation agent for formamidinium lead iodide (FAPbI3) films. Compared with other passivation methods, the room-temperature BAAc capping layer (BAAc RT) demonstrates more uniform and thorough passivation of surface defects inthe FAPbI3 perovskite. Additionally, it provides better energy level alignment for hole extraction. As a result, the champion n-i-p perovskite solar cell with a BAAc capping layer exhibits a power conversion efficiency (PCE) of 24.76%, with an open-circuit voltage (Voc) of 1.19V, and a Voc loss of ≈330mV. The PCE of the perovskite mini-module with BAAc RT reaches 20.47%, showcasing the effectiveness and viability of this method for manufacturing large-area perovskite solar cells. Moreover, the BAAc passivation layer also improves the long-term stability of unencapsulated FAPbI3 perovskite solar cells, enabling a T80 lifetime of 3500h when stored at 35% relative humidity at room temperature in an air atmosphere.