High-surface area carbons from renewable sources with a bimodal micro-mesoporosity for high-performance ionic liquid-based supercapacitors

Highly porous materials with a bimodal pore size distribution in the micro-mesopore range have been produced from biomass by adding melamine to the hydrochar/KOH mixture used in the activation process. These carbons are characterized by BET surface areas in excess of ∼3300 m² g⁻¹ and a porosity equally distributed between micropores and mesopores. The use of melamine in the synthesis process not only extends the pore size distribution into the mesopore region, but leads to the incorporation of a certain amount of nitrogen atoms into the carbon framework. These materials combine high ion adsorption capacities (micropores) and enhanced ion-transport kinetics (mesopores) leading to an outstanding capacitive performance in ionic liquid-based supercapacitors. Thus, they have specific capacitances >160 F g⁻¹ at 1 A g⁻¹ and >140 F g⁻¹ at 60 A g⁻¹ in both pure ionic liquid and in acetonitrile-diluted ionic liquid, enabling these materials to store up to a maximum of ca. 60 W h kg⁻¹ in both kinds of electrolytes and deliver ca. 20 W h kg⁻¹ at ∼42 kW kg⁻¹ (discharge time ca. 2 s) in pure ionic liquid and ∼25–30 W h kg⁻¹ at ∼97–100 kW kg⁻¹ (discharge time ∼1 s) in acetonitrile-diluted ionic liquid.     

Modelling the effects of charge redistribution during self-discharge of supercapacitors

A recent study has shown that the process of self-discharge is determined by a number of parameters such as initial voltage, temperature, and charge duration. Depending on these parameters we observed a voltage decay of 5-15% within 48 h after charging. These observations hardly affect dynamic operations for supercapacitors, but have major implications for all static setups. A complex electrical model has been established to account for the redistribution effects of ions occurring in supercapacitors. Intense experimental studies suggest that these redistribution effects are in part responsible for the measured potential decays. Extended charging allows the ions to allocate themselves more homogeneously throughout the pores and therefore the voltage decay during the rest period following the charging is greatly reduced. The introduced model is capable of predicting the effects of charge duration, initial voltage, and temperature on the open circuit voltage decay.     

氰酸盐离子液体在石墨烯基超级电容器中的应用

将石墨烯电极与离子液体N-甲基-N-丙基吡咯烷氰酸盐（[C₃mpyr][OCN]）/碳酸丙烯酯（PC）混合电解液组装成超级电容器,采用循环伏安（CV）、交流阻抗（EIS）、恒电流充放电（GCD）等方法研究了其在50、60、70℃环境下的电化学性能。结果表明：该体系在较高温度下的电化学性能优异,70℃下其比容量最高可达295 F·g^-1,能量密度可达118 W·h·kg^-1,且恒电流充放电循环稳定性较好。     

Preparation and characterization of imidazolyl ionic liquid-based shear thickening dispersion system

Shear thickening liquid (STF) is a new nonNewtonian fluid widely used in industrial production. In this paper, a novel shear thickening and dispersing system, namely poly methyl methacrylate (PMMA)/1-butyl-3-methylimidazole hexa-fluorophosphate ([BMIM]PF₆), was prepared using ultrasonic with PMMA as the dispersing phase and [BMIM]PF₆ as the dispersing medium. The stability, thixotropic, reversibility, rheology, and viscoelasticity of the dispersion system was studied, respectively. The dispersed system has good stability. The dispersed system shows high response sensitivity to shear rate, as well as good reversibility to shear thickening. Compared with traditional silicon dioxide/polyethylene glycol dispersion system, PMMA/[BMIM]PF₆ dispersion system displays a significantly enhanced shear thickening effect. Nonionic surfactant triton X-100 of 4 wt% can greatly improve PMMA/[BMIM]PF₆ dispersion system's shear thickening behavior. This paper provides a new idea for the further development of protective materials by using STF.     

Investigating acidic ionic liquid-based ultrasonic-assisted extraction of leonurine from Herba Leonuri

An ultrasonic-assisted extraction (UAE) method based on the acidic ionic liquid (IL) of 1-methyl-3-H-imidazolium hydrogen sulfate ([HMIM][HSO₄]) has been successfully developed to extract leonurine from Herba Leonuri. The results indicate that the acidity of the IL has remarkable effect on the extraction efficiency. In addition, several parameters affecting the extraction efficiency, such as ultrasonic power and time, concentration of IL and solid-liquid ratio, were also optimized. Using the proposed approach, the extraction efficiency of leonurine from Herba Leonuri powder reached 0.136‰ within 30 min using only 20 mL of 1 mol·L^?1 [HMIM][HSO₄] aqueous solution.     

萃取还原法制备离子液体基银纳米流体

在1-(2-羟基乙基)-3-甲基咪唑六氟磷酸/硫酸铵 双水相体系中,以双硫腙为萃取剂,将水相中的银离子萃取到离子液体相中.在超声辅助条件下通过对离子液体相中银离子的还原,制备了在亲水性离子液体中稳定的纳米银流体.用纳米粒度仪、透射电子显微镜对该流体进行表征,结果表明,纳米银微粒的平均粒度在29 nm左右,在离子液体中分布均匀.红外光谱分析结果表明,双硫腙与纳米银微粒之间存在一定的化学键作用,双硫腙对纳米银起到表面修饰的作用,这使得纳米银微粒在离子液体中有良好的分散性和稳定性.     

离子液体基萃取体系用于卤水中锂分离的研究进展

近年来,锂电行业的迅猛发展,使锂资源,特别是卤水锂资源的开发利用受到了广泛关注。离子液体作为一种新型的绿色介质为优化升级传统溶剂萃取法卤水提锂带来了新机遇。本文首先简要回顾了离子液体基萃取体系用于卤水提锂的发展历程,重点阐述了离子液体萃取分离锂的行为与性能,详细讨论了萃取机理,并简单介绍了其他基于离子液体的锂分离技术。在此基础上进一步分析了离子液体基萃取体系存在的问题, 提出深入开展离子液体基萃取体系用于盐湖锂分离的机理研究并开发新型离子液体萃取剂及萃取体系,建立和优化新型萃取工艺是未来的主要发展方向。本文期望为盐湖锂资源的绿色、高效开发提供借鉴与参考。     

离子液体基工质对的吸收制冷循环性能实验研究

分别对以离子液体1-乙基-3-甲基咪唑磷酸二乙酯[Emim][DEP]为吸收剂的二元工质对[Emim][DEP]+H₂O和以[Emim][DEP]+LiBr为吸收剂的三元工质对LiBr+[Emim][DEP]+H₂O的吸收制冷循环性能进行了实验研究,用于评价这种新型的工质对的制冷性能。实验结果表明,二元工质对[Emim][DEP]+H₂O具有吸收制冷性能,但与LiBr+H₂O工质对相比,其制冷系数较低。当发生温度为90℃、循环水温度为30℃、蒸发温度在10～15℃时,制冷系数仅为0.16～0.28。主要原因是[Emim][DEP]+H₂O工质对具有较高的黏度和较低的热导率,导致吸收器降膜吸收传热系数较低,吸收器吸收水蒸气的能力不足。为了强化其制冷效果,在[Emim][DEP]+H₂O工质溶液中加入少量LiBr水溶液,构成三元工质对LiBr+[Emim][DEP]+H₂O。实验结果表明,三元工质对LiBr+[Emim][DEP]+H₂O的制冷性能优于二元工质对[Emim[DEP]+H₂O,在上述蒸发温度范围内,制冷系数能够达到0.17～ 0.34,并且制冷温度更低。     

离子液体型超级电容器软包高温老化性能评测研究

构筑了介孔炭,离子液体（EMIMBF₄）与泡沫铝极片结构的超级电容器软包（容量为40 F）,评测了其在2.7 V,65℃,1500 h老化实验中的性能。利用恒流充放电、恒流-恒压充放电模式评测,该电容器经过连续1500 h的高温处理后电容值衰减约10%,内阻增加比例低于40%。与传统的乙腈基电解液软包对比,虽然乙腈基软包起始内阻低,但产气多,且高温循环条件下容量衰减比例和内阻增加比例均劣于离子液体基电解液。上述对比说明,离子液体基电解液在泡沫铝三维导电导热结构的配合下,具有了良好的长周期循环性能。同时,由于其无毒性,可以用于封闭的楼宇空间或其他场所,提供本质安全性。     

Organic di-radical rechargeable battery with an ionic liquid-based gel polymer electrolyte

We employed 1-ethyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide (EMImTFSI)-based gel polymer electrolyte (ILPE) of low viscosity to prevent the instability of the di-TEMPO organic (DTO) electrode with enhancement of the cycle ability and rate-capability. The gel polymer electrolyte was prepared by electrospinning process. The DTO//ILPE//Li cell showed high initial capacity of 80mAh g^-1 for 1 C and 68mAh g^-1 for 10 C-rate, which corresponds to 100 and 85% of theoretical capacity, respectively. The cycle ability and rate-capability were much improved by using of EMImTFSI-based gel polymer electrolyte without self-discharge.     

PEO-imidazole ionic liquid-based electrolyte and the influence of NMBI on dye-sensitized solar cells

1-Oligo(ethylene oxide)-3-methylimidazolium iodide (PEOMImI) was synthesized and applied to dye-sensitized solar cells (DSSCs) by blending it with different 1-alkyl-3-methylimidazolium iodides used as ionic liquid electrolytes. The 1-propyl-3-methylimidazolium iodide (PMII) blend enabled the DSSC to attain a higher solar energy conversion efficiency of 4.52% under a light intensity of 100 mW cm⁻². The addition of N-methylimidazole (NMBI) to the electrolytes increased the conversion efficiency as compared to DSSCs based on NMBI-free electrolytes. The addition of both 1-allyl-3-methylimidazolium iodide (AMII) and NMBI enabled DSSCs to reach their highest solar energy conversion efficiency of 6.14% under a light intensity of 100 mW cm⁻². The ionic conductivity and diffusion coefficient of the triiodide were found to be augmented dramatically after adding NMBI, which leads to an increase in the photocurrent density. The enhancement mechanism of NMBI in the electrolyte was investigated by Raman spectroscopy and differential scanning calorimetry, and it was mainly due to the enhancement of electron exchange in electrolytes.     

Systematic screening procedure and innovative energy-saving design for ionic liquid-based extractive distillation process

In the traditional extractive distillation process, organic solvents are often used as entrainers. However, environmental influence and high energy-consumption are significant problems in industrial application. In this study, a systematic screening strategy and innovative energy-saving design for ionic liquid-based extractive distillation process was proposed. The innovative energy-saving design focused on the binary minimum azeotrope mixtures isopropanol and water. Miscibility, environmental impact and physical properties (e.g., melting point and viscosity) of 30 ionic liquids were investigated. 1-Ethyl-3-methyl-imidazolium dicyanamide and 1-butyl-3-methyl-imidazolium dicyanamide were selected as candidate entrainers. Feasibility analysis of these two ionic liquids was further performed via residue curve maps, isovolatility line and temperature profiles. An innovative ionic liquid-based extractive distillation process combining distillation column and stripping column was designed and optimized with the objective function of minimizing the total annualized cost. The results demonstrate that the total annualized cost was reduced by 19.9% with 1-ethyl-3-methyl-imidazolium dicyanamide as the entrainer and by 24.3% with 1-butyl-3-methyl-imidazolium dicyanamide, compared with that of dimethyl sulfoxide. The method proposed in this study is conducive to the green and sustainable development of extractive distillation process.     

Improved accessibility of porous carbon electrodes with surfactant ionic liquids for supercapacitors

Journal of Applied Electrochemistry - Ionic liquids (ILs) are promising electrolytes for supercapacitors due to their wide electrochemical window. However, most ILs are viscous in nature and...     

High performance supercapacitors based on reduced graphene oxide in aqueous and ionic liquid electrolytes

Partially reduced graphene oxide (RGO) has been fabricated using hydrobromic acid. Since hydrobromic acid is a weak reductant, some oxygen functional groups which are relatively stable for electrochemical systems remain in RGO. Therefore, RGO can be re-dispersed in water and 2–3 layers of graphene can be observed by transmission electron microscopy, showing excellent affinity with water. RGO facilitates the penetration of aqueous electrolyte and introduces pseudocapacitive effects. Moreover, its capacitive nature is enhanced after cycling measurements. It is concluded that the increase of capacitance is due to the reduction of the oxygen functional groups by the cyclic voltammetry and electrochemical impedance spectroscopy analysis. The electrochemical properties in the ionic liquid electrolyte, 1-butyl-3-methylimidazolium hexafluorophosphate (BMIPF₆), are also investigated. At a current density of 0.2 A g⁻¹, the maximum capacitance values of 348 and 158 F g⁻¹ are obtained in 1 M H₂SO₄ and BMIPF₆, respectively.     

Acidic protic ionic liquid-based deep eutectic solvents capturing SO2 with low enthalpy changes

With the aim of lowering energy consumption for gas regeneration, rational design of absorbents with low absorption enthalpy changes while retaining good gas solubility is of both scientific and practical significance. Herein, we demonstrated that acidic protic ionic liquid (APIL)-based deep eutectic solvents (DESs), which comprise N-ethylimidazole hydrochloride ([EimH]Cl) and ethylene glycol (EG), were able to reversibly absorb SO₂ with high solubility (11.60 mol kg⁻¹) and SO₂/CO₂ selectivity (655) at 293.2 K and 101.3 kPa. Meanwhile, [EimH]Cl/EG DESs exhibit very low enthalpy changes (Δ_rH_m) ranging from −27.1 to −25.6 kJ mol⁻¹, and thus ease of desorption at very mild temperature conditions (303.2 K) with desorption ratios up to 99.6%. Recycling experiments showed that no obvious loss in capacity was found after six absorption–desorption cycles, suggesting good regeneration performance of [EimH]Cl/EG DESs. Moreover, spectroscopic analysis revealed the charge-transfer interaction between [EimH]Cl/EG and SO₂.     

Surfactant-free ionic liquid-based nanofluids with remarkable thermal conductivity enhancement at very low loading of graphene

We report for the first time the preparation of highly stable graphene (GE)-based nanofluids with ionic liquid as base fluids (ionic liquid-based nanofluids (Ionanofluids)) without any surfactant and the subsequent investigations on their thermal conductivity, specific heat, and viscosity. The microstructure of the GE and MWCNTs are observed by transmission electron microscope. Thermal conductivity (TC), specific heat, and viscosity of these Ionanofluids were measured for different weight fractions and at varying temperatures, demonstrating that the Ionanofluids exhibit considerably higher TC and lower viscosity than that of their base fluids without significant specific heat decrease. An enhancement in TC by about 15.5% and 18.6% has been achieved at 25 °C and 65 °C respectively for the GE-based nanofluid at mass fraction of as low as 0.06%, which is larger than that of the MWCNT-dispersed nanofluid at the same loading. When the temperature rises, the TC and specific heat of the Ionanofluid increase clearly, while the viscosity decreases sharply. Moreover, the viscosity of the prepared Ionanofluids is lower than that of the base fluid. All these advantages of this new kind of Ionanofluid make it an ideal fluid for heat transfer and thermal storage.     

Electropolymerization of poly(3-methylthiophene) in pyrrolidinium-based ionic liquids for hybrid supercapacitors

The ionic liquids (ILs) N-butyl-N-methyl-pyrrolidinium trifluoromethanesulfonate (PYR₁₄Tf) and N-methyl-N-propyl-pyrrolidinium bis(fluorosulfonyl)imide (PYR₁₃FSI) are investigated as electropolymerization media for poly(3-methylthiophene) (pMeT) in view of their use in carbon/IL/pMeT hybrid supercapacitors. Data on the viscosity, solvent polarity, conductivity and electrochemical stability of PYR₁₄Tf and PYR₁₃FSI as well as the effect of their properties on the electropolymerization and electrochemical performance of pMeT, which features >200 Fg⁻¹ at 60 °C when prepared and tested in such ILs, are reported and discussed; the results of the electrochemical characterization in N-butyl-N-methyl-pyrrolidinium bis(trifluoromethanesulfonyl)imide of the so-obtained pMeT are also given, for comparison.     

A sequential separation of linderane and norisoboldine using supercritical fluid and ionic liquid-based ultrasonic-assisted extraction from Lindera aggregate

ABSTRACT

Linderane (LDR) and norisoboldine (NOR) are two typical active compounds in Lindera aggregate (Sims.) Kosterm. In this study, a new method of sequential extraction of LDR and NOR from L. aggregate was developed by supercritical fluid extraction (SFE) and ionic liquid-based ultrasonic-assisted extraction (IL-UAE) for the first time. The suitable SFE with CO₂ conditions for LDR were 60 min dynamic extraction time, 40°C temperature and 30 MPa pressure. And the optimal IL-UAE factors for NOR were 2.06 mol/L 1-butyl-3-methylimidazolium bromide ([Bmim] Br) aqueous solution, 44 mL/g liquid–solid ratio, and 67 min ultrasonic time. Compared with the traditional extraction process, the sequential methods not only can obtain higher extraction efficiency, but also can realize the selective extraction for two different kinds of constituents with less consumption of traditional organic solvent. In addition, this environmentally friendly method could be used in a large-scale industry.     

Mechanism of self-discharge in graphite-lithium anode

In order to evaluate the anode contribution to the lithium-ion battery self-discharge, three electrode coin cells composed of metallic lithium as reference and counter electrode, organic liquid electrolyte and graphite composite working electrode were constructed as test cells. They were first cycled for a dozen cycles and then stored in the full lithiated state of graphite, at 70 °C for periods from 1 to 8 days. The capacity loss was determined during the first delithiation following storage. The latter was found composed of two terms, a reversible and an irreversible one, where the relative amounts are storage time dependants. Electrochemical impedance spectroscopy (EIS) was used to investigate the changes in the cell interfacial characteristics. A model involving the formation of an absorbed electron-ion-electrolyte complex on the graphite surface is proposed as the mechanism of the reversible and irreversible capacity losses. It is also suggested that precipitation/dissolution reactions are taking place at the solid electrolyte interphase (SEI). Precipitation occurs with insoluble inorganic species such as, LiF and Li₂CO₃, whereas dissolution may concern the organic and/or polymer part of the SEI. The continuous growth of the inorganic (and most resistive) part of the SEI with the subsequent electrode isolation is proposed as the major mechanism of the electrode end of life.