Effect of Conducting Salts in Ionic Liquid Electrolytes for Enhanced Cyclability of Sodium-Ion Batteries.

The electrochemical performance of ionic liquid electrolytes containing different sodium salts dissolved in 1-butyl-1-methylpyrrolidinium bis(trifluoromethylsulfonyl)imide (BMPTFSI) evaluated in a half-cell configuration using spherical P2-Na0.6Co0.1Mn0.9O2+z (NCO) cathodes are reported. Among the various electrolytes investigated, sodium bis(fluorosulfonyl)imide (NaFSI) (0.5 M) in BMPTFSI shows the best electrochemical performance with a significant improvement in cycling stability (90% capacity retention after 500 cycles at 50 mA g-1 in a half cell versus Na metal anode) compared with conventional NaClO4 (1 M) in ethylene carbonate/propylene carbonate electrolytes (39% retention after 500 cycles). Cyclic voltammetry (CV) studies reveal that ionic liquid electrolytes are stable up to 4.8 V versus Na/Na+. When NaFSI and NaTFSI are used as conducting salts, X-ray photoelectron spectroscopy results prove that the cathode electrolyte interface (CEI) is composed of components resulting from the decomposition of the TFSI anion and the deposition of the BMP cation. On the other hand, the CEI layer of the electrode cycled in an electrolyte containing NaClO4 in BMPTFSI follows a different pathway of TFSI decomposition and consists mainly of sodium fluoride. Similarly, plating studies were used to understand the stability of different ionic liquids in contact with metallic sodium. It was found that the excellent capacity retention for the electrolyte consisting of NaFSI salt is related to the formation of a stable CEI and solid electrolyte interphase layers.

Olefin Epoxidation in Aqueous Phase Using Ionic-Liquid Catalysts.

Hydrophobic imidazolium-based ionic liquids (IL) act as catalysts for the epoxidation of unfunctionalized olefins in water using hydrogen peroxide as oxidant. Although the catalysts are insoluble in both the substrate and in water, surprisingly, they are very well soluble in aqueous H2 O2 solution, owing to perrhenate-H2 O2 interactions. Even more remarkably, the presence of the catalyst also boosts the solubility of substrate in water. This effect is crucially dependent on the cation design. Hence, the imidazolium perrhenates enable both the transfer of hydrophobic substrate into the aqueous phase, and serve as actual catalysts, which is unprecedented. At the end of the reaction and in absence of H2 O2 the IL catalyst forms a third phase next to the lipophilic product and water and can easily be recycled.

Influence of substituents on cation-anion contacts in imidazolium perrhenates.

A series of imidazolium perrhenates with different substituents at the imidazolium ring were synthesised and characterised, including single crystal X-ray diffraction. The effect of the substitution pattern on the state of aggregation of the compounds, the charge delocalisation and the ion pairing interaction via hydrogen bonds was studied. Particularly the substitution at the C2 position of the imidazolium ring was shown to be crucial to fine-tune the ion contacts. Fluorinated substituents appear to exhibit enhanced interionic interactions. The ability to tune the degree of contacts of the perrhenate anion allows for adjusting the nucleophilicity of this anion.

Catalytic epoxidation by perrhenate through the formation of organic-phase supramolecular ion pairs.

Organic-phase supramolecular ion pair (SIP) host-guest assemblies of perrhenate anions (ReO4(-)) with ammonium amide receptor cations are reported. These compounds act as catalysts for the epoxidation of alkenes by aqueous hydrogen peroxide under biphasic conditions and can be recycled several times with no loss in activity.

Cycloaddition of carbon dioxide and epoxides using pentaerythritol and halides as dual catalyst system.

The combination of pentaerythritol with nucleophilic halide salts such as nBu4NI is used as a dual catalyst system for the cycloaddition of carbon dioxide (CO2) with a broad range of organic epoxides yielding the respective cyclic carbonates. Due to synergistic effects of the organocatalysts, excellent yields and selectivities could be achieved under mild reaction conditions. Moreover, the nontoxic, cost-efficient, and readily available system is easily recyclable without significant loss of reactivity, representing an exceptional sustainable approach for the fixation of CO2.

Cleavage of C-O bonds in lignin model compounds catalyzed by methyldioxorhenium in homogeneous phase.

Methyldioxorhenium (MDO)-catalyzed C-O bond cleavage of a variety of lignin ß-O-4-model compounds yields phenolic and aldehydic compounds in homogeneous phase under mild reaction conditions. MDO is in situ generated by reduction of methyltrioxorhenium (MTO) and is remarkably stable under the applied reaction conditions allowing its reuse for least five times without significant activity loss. Based on the observed and isolated intermediates, 17 O- and 2 H-isotope labeling experiments, DFT calculations, and several spectroscopic studies, a reaction mechanism is proposed.

Activation of hydrogen peroxide by ionic liquids: mechanistic studies and application in the epoxidation of olefins.

Imidazolium-based ionic liquids that contain perrhenate anions are very efficient reaction media for the epoxidation of olefins with H2O2 as an oxidant, thus affording cyclooctene in almost quantitative yields. The mechanism of this reaction does not follow the usual pathway through peroxo complexes, as is the case with long-known molecular transition-metal catalysts. By using in situ Raman, FTIR, and NMR spectroscopy and DFT calculations, we have shown that the formation of hydrogen bonds between the oxidant and perrhenate activates the oxidant, thereby leading to the transfer of an oxygen atom onto the olefin demonstrating the special features of an ionic liquid as a reaction environment. The influence of the imidazolium cation and the oxidant (aqueous H2O2, urea hydrogen peroxide, and tert-butyl hydrogen peroxide) on the efficiency of the epoxidation of cis-cyclooctene were examined. Other olefinic substrates were also used in this study and they exhibited good yields of the corresponding epoxides. This report shows the potential of using simple complexes or salts for the activation of hydrogen peroxide, owing to the interactions between the solvent medium and the active complex.