Yude He

Intrinsic Electric Fields in Ionic Liquids Determined by Vibrational Stark Effect Spectroscopy and Molecular Dynamics Simulation

The electric fields of ionic liquids are only slightly higher than those of common molecular solvents, and are strongly structure-dependent; they noticeably decrease with anion size because of increased separation of ions, and slightly decrease as the alkyl chain elongates due to increasing spatial heterogeneity. These were the key results of vibrational Stark effect spectroscopy and molecular dynamics simulations.

CoO@Co and N-doped mesoporous carbon composites derived from ionic liquids as cathode catalysts for rechargeable lithium–oxygen batteries

The catalytic activity of a cathode material plays a vital role in determining the electrochemical performance of Li–O2 batteries. Herein, N-doped mesoporous carbon-supported CoO@Co nanoparticles are prepared in situ using the ionic liquid (IL) 1-butyl-3-methylimidazolium tetrachlorocobalt ([BMIm]2[CoCl4]) as the precursor with silica as the hard template. The material was characterized by TGA, BET, XRD, TEM, XPS, and H2-TPR. After exposure to air, the species on the surface of the Co is CoO, as verified by XPS. The pore size is about 2 nm, and the CoO@Co nanoparticles were irregularly shaped and sized in the range of 20–300 nm, which may have been due to the aggregation of ultrafine nanoparticles. The existence of an interaction between the CoO@Co nanoparticles and the N-doped support is confirmed by XPS and H2-TPR. The catalyst shows superior activity for oxygen evolution reaction (OER) manifested in its lower charge potential (3.75 V at the current density of 100 mA g−1). Enhanced performances in coulombic efficiency, rate capability, and cycling stability (55 cycles) are also realized. Finally, these improvements, with the exception of the catalytic activity of CoO, may benefit from the interaction between the carbon supporter and the CoO@Co nanoparticles.

Hydrophobic 1-allyl-3-alkylimidazolium dicyanamide ionic liquids with low densities

Nine 1-allyl-3-alkylimidazolium ([ACnIm]) or 1-vinyl-3-alkylimidazolium ([VCnIm]) dicyanamides (DCA) were prepared and characterized, and their physicochemical properties were studied in detail. Except for [AVIm]DCA and [AC4Im]DCA, the other dicyanamides with hexyl or longer alkyl chains on the cation exhibited the characteristic of hydrophobicity. Among them, [AC8Im]DCA and [AC10Im]DCA were found to possess similar densities to water, i.e. 1.007 g cm−3 and 0.988 g cm−3 at 25 °C, respectively. Interestingly, a reversible phase reversion of a [AC8Im]DCA/H2O mixture was observed as the temperature varied. These environmentally-friendly liquid materials have potential applications as precursors for syntheses of conducting polymeric materials.

Preparation of Carbon Nanotubes/Manganese Dioxide Composite Catalyst with Fewer Oxygen-Containing Groups for Li-O2 Batteries Using Polymerized Ionic Liquids as Sacrifice Agent

Considering the significant influence of oxygen-containing groups on the surface of carbon involved electrodes, a carbon nanotube (CNT)-based MnO2 composite catalyst was synthesized following a facile method while using polymerized ionic liquids (PIL) as sacrifice agent. Herein, the PIL (polymerized hydrophobic 1-vinyl-3-ethylimidazolium bis ((trifluoromethyl)sulfonyl)imide) wrapped CNTs were prepared. The composite was applied to support MnO2 by the treatment of KMnO4 solution, taking advantage of the reaction between PIL and KMnO4, which excludes or suppresses the oxidation of CNTs, and the as-synthesized material with fewer oxygen-containing groups acted as a cathode catalyst for Li-O2 batteries, directly avoiding the application of binders. The catalyst shows enhanced activity compared to that of the samples without PIL, as verified by the lower overpotential during discharging and charging (0.97 V at the current density of 100 mA g-1). Meanwhile, the performance parameters such as Coulombic efficiency and rate capability were also improved for the Li-O2 battery utilizing this catalyst. Further, the formation of confined Li2O2 particles could be responsible for the reduction of charge potential of Li-O2 batteries due to the synergy effect of the intrinsic catalytic activity of MnO2 and fewer oxygen functional groups on the catalyst surface.

Separation of dibutyl carbonate/butyl carbamate close-boiling mixture using imidazolium-based ionic liquids

An efficient method using commercially available ionic liquids (ILs) as extractants for the separation of a close-boiling mixture containing dibutyl carbonate (DBC) and butyl carbamate (BC) was provided. It was found that 1-butyl-3-methylimidazolium chloride ([BMIM]Cl) displayed the best performance for the separation of DBC and BC, and the purity of the DBC and BC could reach 99.8% and 99.9%, respectively, under the optimum conditions. According to the results of infrared spectroscopy (IR) and thermogravimetric (TG) analyses, the superiority of [BMIM]Cl might be related to the high nucleophilicity (i.e. ability to hydrogen bond) of the Cl−, which could be able to interact with the amino in BC to form a eutectic mixture and resulted in easy removal of DBC. Meanwhile, no decomposition of [BMIM]Cl was observed in the heating process, and the obtained results showed that [BMIM]Cl could be successfully reused for ten recycles with DBC purity of 99.5% avoiding any further treatment. Moreover, [BMIM]Cl also exhibited good performance in the separation of a dimethyl carbonate/methanol azeotropic mixture.

Binary Mg–Fe oxide as a highly active and magnetically separable catalyst for the synthesis of ethyl methyl carbonate

Magnetic binary Mg–Fe oxides were prepared by a co-precipitation method, characterized and tested in the synthesis of ethyl methyl carbonate (EMC) from di methyl carbonate (DMC) and diethyl carbonate (DEC). The obtained results showed that the Mg/Fe oxide catalyst with a 1 : 1 molar ratio and calcined at 400 °C exhibited superior catalytic activity. The yield of EMC could reach 66% (at 100 °C for 1.5 h) with a TOF of 220 mmol h−1 gcat−1. The prepared catalysts could be magnetically separated, and reused for ten runs without noticeable deactivation. XRD and Mossbauer spectra revealed that there was a synergistic effect between Mg and Fe oxides in the catalysts, which was consistent with the results of TPR, i.e. the introduction of the Mg component favored the reduction of the Fe2O3. XPS and IR characterizations indicated that there were a large number of accessible Fe-OHs on the surface of MgFe-400, and combining the Fe-OHs with the basic MgO may be related to the highly catalytic performance.