Room Temperature Molten Salts Research Articles

Development of a wafer cooling system using ionic liquid under high vacuum condition for semiconductor fabrication device

Herein, vacuum-compatible semiconductor-wafer-immersion-cooling method is proposed as an alternative to helium gas cooling, which becomes challenging to maintain in high-vacuum conditions during semiconductor manufacturing. This method aims to simultaneously maintain a high vacuum and achieve high cooling performance. It involves supplying a low-vapor-pressure ionic liquid (IL), a type of room-temperature molten salt, into the gap between the wafer and the wafer stage, using liquid pressure to float and cool the wafer. The proposed cooling device was prototyped, and experimentally investigated the IL cooling performance. The results showed that, even under high vacuum with order of 10−4 Pa, IL can fully immerse the 80 μm-scale small clearance between wafer and wafer stage and demonstrate high cooling performance for heated wafers. The proposed method has been proven to achieve both high vacuum and high cooling performance. It is expected as an alternative to helium gas cooling in semiconductor manufacturing.

Thermal stabilities and decomposition mechanisms under oxygen and nitrogen atmospheres for imidazolium ionic liquids with different cations

Ionic liquids (ILs) are room temperature molten salts, have received extensive attention from the academic community due to their excellent characteristics. In the context of global warming, more and more scholars are looking forward to using ILs as a gas adsorbents, especially ILs containing bis(trifluoromethylsulfonyl)imine (Tf2N). It is well known that the thermal stabilities of ILs are affected by many factors, and the cation type is one of them. In this paper, five imidazole ILs with different functional groups on the side chains of the imidazole rings were selected as the research objects, and their anions were all Tf2N. The thermal decomposition characteristics and thermal effects of the selected samples were determined by thermal gravimetric analyzer (TGA) and differential scanning calorimetry (DSC). The experimental data showed that the most stable ionic liquid was that with the simplest side chain, and the more complex the side chain was, the lower the thermal stability of the sample. In addition, some of their decomposition products were studied with thermogravimetric analyzer coupled with Fourier-transform infrared spectrometry (TG–FTIR). The decomposition mechanisms of the samples did not change under different atmospheres.

High Energy Density Porous RuO2 micro-Supercapacitors Using Protic Ionic Liquid Electrolytes

The rapid development of the Internet of Things (IoT) demands reliable and long-term energy supply to microelectronic devices distributed over the network with high power performance and less maintenance required.[1] Micro-supercapacitors (MSCs) have come to the foreground as miniaturized energy storage devices showing outstanding power density and long cycle life. However, the low cell voltage and low energy density remain major bottleneck that prevents their adoption in real device applications. To this end, several studies have been devoted to the engineering of MSC electrode materials and structural architecting of current collectors within the limited available footprint. This approach could offer opportunities to enhance the electrochemically active surface and mass loading of active materials with fast ion diffusion kinetics, leading to high areal energy density performance.[2] Although several efforts have been put forth in this direction, the complex synthesis route, unfavourable interfacial and mechanical stability of the electrode, electrolyte compatibility issues, etc. remain an arduous challenge.[3] The low cell voltage is another major issue preventing from achieving high energy density values in MSCs as it is directly linked to the electrochemical stability window (ESW) of the electrolytes used.[4] In addition, liquid-state electrolytes currently employed are inappropriate for the microfabrication route as it is prone to evaporation, leakage, and potential safety issues. Hence, a lot of research attention has been given to developing solid-state electrolytes able to afford large operational windows and help promote the application of on-chip MSCs. In this work, we have demonstrated the use of protic ionic liquid (PIL)-based electrolytes able to provide pseudocapacitance in hydrous ruthenium dioxide (RuO2) electrodeposited on interdigitated MSC substrates with extended operational cell voltage. As a pseudocapacitive material, RuO2 exhibits excellent conductivity, high electrochemical reversibility, and cycling stability.[5] On the other hand, as room temperature molten salts, PILs help to overcome evaporation and encapsulation problems associated with the conventional aqueous electrolytes and flammability and safety issues linked to common organic electrolytes.[6-9] We explored pyrrolidinium-based PILs with varying alkyl substitutions, their structure-property, and electrochemical studies for RuO2 MSCs. To further expand the use of these PILs in real devices, 3D MSCs with higher active material mass loading was realised using interdigitated porous Au current collector substrates. The PIL-based porous RuO2 MSCs showed superior charge storage and higher energy density performance as compared to conventional aqueous electrolytes. To envision the practical application of RuO2 MSCs and their subsequent integration with microelectronic devices, ionogel-based solid-state electrolytes were developed. This work opens pathways to develop micro-supercapacitors exhibiting high energy and power density by combining pseudocapacitive metal oxide-based active materials and protic ionic-liquid-based non-aqueous electrolytes and help their integration with on-chip IoT devices.

Self-doped TiO2 nanotubes with surface modification by ionic liquids for enhanced photoreduction of CO2 to acetic acid

The photocatalytic reduction of CO2 to high-value hydrocarbons can both solve environmental problems and alleviate the energy crisis. As a room-temperature molten salt with designable anions and cations, ionic liquids are very popular in the field of CO2 capture. If combining ionic liquids with photocatalysts, simultaneous capture and conversion of CO2 are expected to be achieved. In this study, a [bmim][Tf2N] loaded self-doped TiO2 nanotubes (ILs-RTNTs) composite photocatalyst was developed for the photoreduction of CO2 to acetic acid. The acetic acid yield of ILs-RTNTs reached as high as 88.1 μmol gcat−1h−1, and there was no decrease after six cycles. Both the defects constructed by self-doping and the surface modification by ionic liquids strengthened the light utilization ability of the photocatalyst and enhanced the separation of photoinduced electron-hole pairs. Density-functional theory (DFT) calculations further revealed that the surface loading of ionic liquids introduced more active sites, strengthened the adsorption of CO2, changed the electronic structure, and lowered the energy barrier for electron transfer of the photocatalyst. This study will promote the versatile application of ionic liquids in the field of simultaneous capture and photoreduction of CO2.

Machine Learning-Boosted Design of Ionic Liquids for CO2 Absorption and Experimental Verification.

Efficient CO2 capture is indispensable for achieving a carbon-neutral society while maintaining a high quality of life. Since the discovery that ionic liquids (ILs; room-temperature molten salts) can absorb CO2, various solvents composed of molecular ions have been studied. However, it is challenging to observe the properties of each isolated ion component to control the function of ILs as they are mixtures of ions. Finding the optimal cation-anion combination for the CO2 absorbent from their enormous chemical space had been impossible in a practical sense. This study applied electronic structure informatics to explore ILs with high CO2 solubility from 402,114 IL candidates. The feature variables were determined by a set of cheap quantum chemistry calculations for isolated small-ion fragments, and the importance of molecular geometries and electronic states governing molecular interactions was identified via the wrapper method. As a result, it was clearly shown that the electronic states of ionic species must have essential roles in the CO2 physisorption capacity of ILs. Considering synthetic easiness for the candidates narrowed by the machine learning model, trihexyl(tetradecyl)phosphonium perfluorooctanesulfonate was synthesized. Using a magnetic suspension balance, it was experimentally confirmed that this IL has higher CO2 solubility than trihexyl(tetradecyl)phosphonium bis(trifluoromethanesulfonyl)amide, which is the previous best IL for CO2 absorption.

High ionic conductivity of “Room Temperature Molten Salt” based PVA hydrogel electrolyte prepared by electron beam irradiation

In order to improve the safety and environmental friendliness of electrolytes, it is necessary to enhance the ionic conductivity of polyvinyl alcohol (PVA) hydrogel electrolytes. Herein, we present a method for the preparation of PVA hydrogels using electron beam irradiation, and based on this method, a high strength PVA hydrogel with breaking strength of 78 kPa was obtained. It was combined with room-temperature inorganic hydrated molten salt (RTMS) to prepare RTMS-PVA hydrogel electrolytes with a maximum ionic conductivity of 70.6 mS cm−1, and the assembled NaCoHCF/AC aqueous ion battery at 1C The capacity retention after 100 cycles was 98%, achieving a highly stable PVA hydrogel with high ionic conductivity. This protocol is not only cost-effective in terms of raw materials and synthetic routes, simple to operate, and nontoxic, but also provides an avenue to realize large-scale industrial production.

A Versatile Molten-Salt Induction Strategy to Achieve Efficient CsPbI3 Perovskite Solar Cells with a High Open-Circuit Voltage >1.2 V.

All-inorganic CsPbI3 perovskite has emerged as an important photovoltaic material due to its high thermal stability and suitable bandgap for tandem devices. Currently, the cell performance of CsPbI3 solar cells is mainly subject to a large open-circuit voltage (VOC ) deficit. Herein, a multifunctional room-temperature molten salt, dimethylamine acetate (DMAAc) is demonstrated, which not only directly acts as a solvent for precursor solutions, but also regulates the phase conversion process of the CsPbI3 film for high-efficiency photovoltaics. DMAAc can stabilize the DMAPbI3 structure and eliminate the Cs4 PbI6 intermediate phase, which is easily spatially segregated. Meanwhile, a new homogeneous intermediate phase DMAPb(I,Ac)3 is formed, which finally affords high-quality CsPbI3 films. With this approach, the charge capture activity of defects in the CsPbI3 film is significantly suppressed. Consequently, a VOC of 1.25V and >21% power conversion efficiency are achieved, which is the record highest reported thus far. This intermediate phase-regulation strategy is believed to be applicable to other perovskite material systems.

Fluorine Gas Production by Electrolysis of Copper Fluoride in Room-temperature Molten Salt

Fluorine Gas Production by Electrolysis of Copper Fluoride in Room-temperature Molten Salt

General framework for the study of dynamical properties and arrested states of ionic liquids

In this work, we present a first-principles theoretical framework for the description of structural and dynamical behaviors of ionic liquids. This framework applies the self-consistent generalized Langevin equation (SCGLE) theory, which predicts the dynamically arrested states of several physical systems, including charge and size asymmetric ionic liquids. In its current form, the SCGLE is a particularly useful framework for predictions of arrested and partially arrested states in both classical and room-temperature molten salts, electrolytic solutions, and superionic conductors. Some illustrative examples of the predictive power of our framework are presented in this work, showing its potential application in design and development of novel conducting materials.

Understanding the Reversible Electrodeposition of Al in Low-Cost Room Temperature Molten Salts

Al-based batteries are considered an attractive alternative to Li metal batteries due to the use of Al metal as an anode with lower cost, lower reactivity and larger abundance compared to Li. Despite the aforementioned attributes, few electrolytes permit reversible electrodeposition of Al metal at room temperature. Thus, for the last 30 years, expensive imidazolium-based ionic liquids have dominated the field. Even though extensive research has been conducted on imidazolium-based ionic liquids, a systematic study that sheds light on the structural requirements, physicochemical and transport properties required to enable high reversibility has not been conducted. Here, we investigated two ammonium-based systems that show comparable reversibility to imidazolium-based ionic liquids with Coulombic efficiencies up to 99.1% for over 1000 cycles (1 mAh/cm2, 4 mA/cm2). We reveal that high reversibility in ammonium- and imidazolium- based electrolytes is achieved when a critical ratio of the solvation species (AlCl4 - and Al2Cl7 -) is obtained, where Lewis’s acidity and beneficial interfacial reactions continuously etch the Al2O3 resistive interfacial layer and uniform current distribution is attained on the anode. Insights were obtained via construction of phase diagrams, 27Al quantitative NMR, structural considerations, chemical analyses, transport properties and electrochemical measurements. The findings yield quantitative molecular-level understanding of Al electrodeposition in room-temperature ammonium-based molten salts that are up to five times cheaper than the commonly used imidazolium-based electrolytes. The fundamental understanding gained on the structural, physicochemical and transport properties that enable high reversibility of Al electrodeposition in electrolytes can guide engineering approaches for other electrolyte systems for Al-based batteries. Furthermore, the development of low-cost, high-rate capability and long-term stability electrolytes can accelerate the development of high-capacity cathodes leading to higher energy densities relevant for electric vehicles.

“Room Temperature Molten Salt”-Based Polymer Electrolyte Enabling a High-Rate and High-Thermal Stability Hybrid Li/Na-Ion Battery

“Room Temperature Molten Salt”-Based Polymer Electrolyte Enabling a High-Rate and High-Thermal Stability Hybrid Li/Na-Ion Battery

A High Rate and Stable Hybrid Li/Na-Ion Battery Based on a Hydrated Molten Inorganic Salt Electrolyte.

Taking into the consideration safety, environmental impact, and economic issue, the construction of aqueous batteries based on aqueous electrolyte has become an indispensable technical option for large-scale electrical energy storage. The narrow electrochemical window is the main problem of conventional aqueous electrolyte. Here, an economical room-temperature inorganic hydrated molten salt (RTMS) electrolyte with a large electrochemical stability window of 3.1V is proposed. Compared with organic fluorinated molten salts, RTMS is composed of lithium nitrate hydrate and sodium nitrate with much lower cost. Based on the RTMS electrolyte, a hybrid Li/Na-ion full battery is fabricated from cobalt hexacyanoferrate cathode (NaCoHCF) and perylene-3,4,9,10-tetracarboxylic dianhydride (PTCDA) anode. The full cell with the RTMS electrolyte exhibits a fantastic performance with high capacity of 139 mAh g-1 at 1 C, 90 mAh g-1 at 20 C, and capacity retention of 94.7% over 500 cycles at 3 C. The excellent performances are contributed to the unique properties of RTMS with a large electrochemical window, solvated H2 O free and high mobility of Li+ , which exhibits excellent Li-ions insertion and extraction capacity of NaCoHCF. This RTMS cell provides a new economic choice for large-scale energy storage.

Design of carboxylate-based ionic liquids (ILs) containing OH and CF3 groups; influence of intramolecular hydrogen bonds and inductive effect on the binding energy between the cation and anion of ILs, a DFT study

Ionic liquids, which are widely known as room temperature molten salts, have been the subject of much scientific debate for more than a decade.

Synthesis, crystal structure and properties of tris(2-hydroxypropyl)ammonium based protic ionic liquids and protic molten salts

Fifteen tris(2-hydroxypropyl)ammonium salts (TPA salts) were first synthesized by a direct reaction of proton transfer from carboxylic acids to tris(2-hydroxypropyl)amine. The composition and structure of synthesized TPA salts were confirmed by NMR (1H, 13C), FT-IR spectroscopy and elemental analysis. The crystal structure and conformation of the tris(2-hydroxypropyl)ammonium cation in salts of salicylic, nicotinic and malonic acids were studied by single-crystal X-ray diffraction. Thermal stability studies have shown that TPA salts are protic ionic liquids with melting temperatures below 100 °C or room-temperature ionic liquids or molten salts. Selected TPA salts were investigated for their antimicrobial activity against bacterial and fungus strains. In addition, it was shown for the first time that synthesized TPA salts can be used as potential buffer agents for 68Ga-radiolabeling of bifunctional chelating agents (BCA) and clinically relevant peptides (PSMA-11, PSMA-617, DOTA-NOC, DOTA-TATE).

Dielectric properties of sulfonated poly(ether ether ketone) (SPEEK) electrolytes with 1-ethyl-3-methylimidazolium tetrafluoroborate salt: Ionic liquid-based conduction pathways

In this study, dielectric properties of sulfonated poly(ether ether ketone) (SPEEK) solid polymer electrolytes (SPEs) containing room-temperature molten salt, 1-ethyl-3-methylimidazolium tetrafluoroborate were investigated. Additionally, the effects of ionic liquid (IL) addition on the thermomechanical properties and the micro-structure of composite electrolytes (SPEEK-30 × 1IM and SPEEK-30 × 2IM) were studied. The characteristics of the SPEs were investigated by FTIR, SEM, TGA, DSC and DMA measurements. FTIR analysis confirmed the success of the sulfonation process and IL/sulfonated polymer interactions. IL addition caused changes in the crystalline structure and surface morphology of the SPEs. It was observed that SPEEK-30 × 1IM and SPEEK-30 × 2IM electrolytes have lower glass transition temperatures (Tg) and crystallinity than that of pure SPEEK-30. Due to the amorphous character formed by IL, proton conduction paths in which ILs exhibit enhanced conductivity have been formed. Among the composite electrolytes, SPEEK-30 × 2IM demonstrated an ionic conductivity (5.45 × 10−4 Scm-1) more than 20 times higher than SPEEK-30.

Flammability estimation of 1-hexyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide

Ionic liquids (ILs) are known as room temperature molten salts, which are considered green replacement to traditional organic solvents. The fire hazards of traditional organic solvents mainly depend on the combustibility of their vapors, thus ILs are generally regarded as nonflammable owing to their low volatility. However, recent studies show that ILs may combust due to the potential hazards of thermal decomposition, indicating the issue of fire and explosion of ILs are eager to be evaluated during the applications. In this study, the fire and explosion hazards of IL 1-hexyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide ([C6mim][NTf2]) are explored in different aspects. The traditional definition of the flammability for the common organic solvent is not thoroughly applicable to [C6mim][NTf2] due to the low volatility. Furthermore, the common definition of reactivity for traditional organic solvents also fails to apply, because the decomposition reaction is indeed an endothermic reaction. However, the auto-ignition of some decomposition products will result in fire and explosion hazards for [C6mim][NTf2]. Therefore the application of such data in safety purposes should be very careful.

Electrodeposition of Al-Cr-Mn Alloys from Chloroaluminate Ionic Liquids

Despite the emergence of many new ionic liquid systems or room-temperature molten salts, chloroaluminate ionic liquids are still one of the most versatile systems for the electrochemical surface finishing of metals. The most commonly studied chloroaluminate IL is the well-known mixture of AlCl3 and the quaternary ammonium chloride salt, 1-ethyl-3-methylimidazolium chloride (EtMeImCl).1 Among the anhydrous, aprotic ILs prepared to date, this mixture still holds the record for the highest conductivity and lowest viscosity. Save for the need to protect it from exposure to moisture, it is undoubtedly one of the most versatile IL systems for electrochemistry. In most cases, the acidic composition of this IL proves to be the most valuable composition for surface finishing, owing to the presence of the coordinately unsaturated Lewis acidic species, Al2Cl7 -, which is readily reduced to Al metal via the reaction:4Al2Cl7 - + 3e- ⇌ Al + 7AlCl4 - (1)The electroplating of Al from chloroaluminate ILs, such as AlCl3-EtMeImCl, is one of the most thoroughly studied processes in the field of ionic liquid electrochemistry, as attested in a recent review.2 However, much less attention has been devoted to the electrodeposition of aluminum alloys from these ILs, many of which have very useful properties. Stable alloys can be obtained during the electrodeposition of Al if certain low valent transition metal ions, M z +, that are reduced negative of the potential required for the reaction shown in Eq. 1 are added to the acidic IL, e.g., Cr2+, Ti2+, V2+, Mo2+, and Mn2+, to name a few.2 In this case, it is possible to prepare aluminum-transition metal alloys: xM(AlCl4) p (p-z)- + 4(1-x)Al2Cl7 - + [3-(3-z)x]e- ⇌ M x Al1-x + [7(1-x) +px]AlCl4 - (2)where x represents the fraction of the transition metal in the M x Al1-x alloy. For some values of x, these so-called “overpotential alloys” form single-phase metallic glasses. In this case, these amorphous, non-equilibrium alloys exhibit a greatly enhanced resistance to chloride pitting corrosion relative to pure Al. Ternary alloys with metallic glass phases can also be produced by adding a second transition metal to the acidic IL. Articles have appeared in The Journal describing the electrodeposition and properties of such aluminum alloys containing Mn + Mo,3 Mo + Ti,4 and Mn + W.5 In general, coatings prepared with ternary alloys display enhanced resistance to chloride pitting corrosion compared to the corresponding binary alloys. In this poster, we describe recent work on the electrodeposition of Al-Cr-Mn ternary alloys.

Improved Performance of CH3NH3PbI3-xClx Resistive Switching Memory by Assembling 2D/3D Perovskite Heterostructures.

The rapidly growing demand for fast information storage and processing has driven the development of resistive random access memories (RRAMs). Recently, RRAMs based on organometal halide perovskite materials have been reported to have promising memory properties, which are essential for next-generation memory devices. In this study, a hybrid two-dimensional/three-dimensional (2D/3D) perovskite heterostructure has been created by depositing n-butylammonium iodide on top of the CH3NH3PbI3-xClx (MAPbI3-xClx) surface. The perovskite film is fabricated by a facile one-step spin-coating method with room-temperature molten salt methylammonium acetate in the air. Resistive switching memory devices with a 2D/3D perovskite heterostructure exhibit a significantly improved switching window (ON/OFF ratio over 103) with a lower operation voltage compared with their 3D counterparts. The 2D/3D perovskite heterostructure is advantageous for fabricating uniform-crystalline-grain, highly compact structures and can passivate defect states for the MAPbI3-xClx film and the interface, which results in improved memory properties. These results provide a new perspective for developing high-performance perovskite-based memory devices.

Polymeric room-temperature molten salt as a multifunctional additive toward highly efficient and stable inverted planar perovskite solar cells

We for the first time report the application of a polymeric room-temperature molten salt in high efficiency and excellent stability inverted perovskite solar cells.

Ion beam generation from a protic ionic liquid source with an externally wetted tungsten needle

Ionic liquid ion sources (ILISs) are similar to liquid metal ion sources and use ionic liquids (i.e., room temperature molten salts) instead of liquid metals. Aprotic ionic liquids have been used in most cases, whereas protic ion liquids have hardly been used thus far. In this study, propylammonium nitrate (PAN), which is a protic ionic liquid, was tested as the liquid material for an ILIS. Beam generation was investigated in DC operation using a tungsten needle externally wetted with PAN. Experimental results showed that a stable ion beam was generated without special measures and that the ion beam contained cluster ions with m/z values on the order of 103. Additionally, electrochemical experiments were performed in vacuum to investigate electrochemical reactions involved in beam generation. Residual gas analysis revealed that H2O and O2 were electrochemically produced at a tungsten electrode immersed in PAN. These products will probably result from electrochemical reactions of water in PAN because protic ionic liquids contain a small amount of water even in vacuum. The stability of the ion beam can be explained by the effect of water in PAN.