Stabilisation of the superoxide anion in bis(fluorosulfonyl)imide (FSI) ionic liquid by small chain length phosphonium cations: Voltammetric, DFT modelling and spectroscopic perspectives

Ionic liquids (ILs) containing the bis(fluorosulfonyl)imide anion, FSI, have been investigated as electrolytes for metal-air batteries. Full chemical reversibility is found for the reduction of oxygen to superoxide at 60 degrees C under short time scale conditions of cyclic voltammetry at a glassy carbon electrode when the IL contains the small chain length triisobutyl(methyl)phosphonium rather than a pyrrolidinium cation. DFT calculations suggest that this is a consequence of the higher ion pair association energy and shorter intermolecular distance associated with the interaction of the superoxide anion with the phosphonium cation. Stabilization on longer timescales was also established by spectroscopic techniques when the phosphonium based ILs were exposed to KO2. Studies on superoxide stability in related ionic liquids containing the triisobutyl(methyl)phosphonium cation with the fluorosulfonyl(trifluoromethanesulfonyl)imide, FTFSI, or bis(trifluoromethanesulfonyl)imide, TFSI, anions are also reported.

Towards phosphorus free Ionic liquid anti-wear lubricant additives

The development of improved anti-wear additives would enable the use of lower viscosity oils that would lead to improved efficiency. Ionic liquids have the potential to be this type of new anti-wear additive. However, currently the best performing ionic liquids that are miscible in non-polar base oils, the phosphonium phosphates, contain phosphorus on both the cation and anion. Manufacturers are seeking to reduce the presence of phosphorus in oils. Here, as a first step towards phosphorus-free anti-wear additives, we have investigated ionic liquids similar to the phosphonium phosphates but having either a phosphorus-free cation or anion. Two quaternary ammonium phosphates (N6,6,6,14)(BEHP) and (N8,8,8,8)(BEHP) and a phosphonium silyl-sulfonate (P6,6,6,14)(SSi) were compared to a phosphonium phosphate (P6,6,6,14)(BEHP) and a traditional zinc dithiophosphate (ZDDP) as anti-wear additives in mineral oil. The change from a phosphonium to a quaternary ammonium cation drastically reduced the miscibility of the Ionic liquid (IL) in the oil, while the change to a smaller silicon containing anion also resulted in limited miscibility. For the pin-on-disk wear test conditions used here none of the ionic liquids outperformed the ZDDP except the (P6,6,6,14)(BEHP) at a relatively high loading of 0.10 mol·kg−1 (approximately 8 wt%). At a more moderate loading of 0.025 mol·kg−1 the (P6,6,6,14)(SSi) was the best performing ionic liquid by a significant amount, reducing the wear to 44% of the neat mineral oil, while the ZDDP reduced the wear to 25% of the mineral oil value. Electron microscopy and energy dispersive X-ray spectroscopy showed that the presence of a silicon containing tribofilm was responsible for this protective behaviour, suggesting that silicon containing ionic liquids should be further investigated as anti-wear additives for oils

Synthesis and characterization of amino acid ionic liquids and low symmetry ionic liquids based on the triaminocyclopropenium cation.

This thesis involves the synthesis of two main classes of triaminocyclopropenium (tac) Ionic Liquids (ILs) (i) Amino Acid Ionic Liquids (AAILs) and (ii) reduced-symmetry cations. [C₃(NEt₂)₂(NRR’)]X (X = TFSA and MeSO₄) were prepared, whereby NHR is derived from amino acids. Optically pure AAILs, [E₄AminoAcid]X (X = TFSA and MeSO₄) were obtained as a mixture of the IL and its zwitterion. The ratios of these mixtures were determined by pH titration and microanalysis. The AAILs specific rotations and pKa values were determined. AAILs can be used for chiral discrimination and form diasterreomeric salts with the entioenriched sodium salt of Mosher’s acid. The AAILs were also successfully used as a solvent and/or catalyst in an aldol reaction and a Diels-Alder reaction. The low-molecular weight series, [C₃(NMe₂)₂(NRR’)]X and [C₃(NMe₂)₂(NR’2)]X was synthesized and characterized: protic ILs NRR’, where R = ethyl, propyl, allyl, butyl, - CH2CH2OCH₃ and pentyl, R’ = H and X = TFSA: and aprotic ILs NRR’, where R = Me, R’ = ethyl, allyl, propyl, butyl, -CH2CH2OCH₃ and hexyl and X = TFSA and DCA. ILs with C2v symmetry [C₃(NEt₂)₂(NH2)]X (X = TFSA and MeSO₄), [C₃(NEt₂)₂(NBu2)]I, [C₃(NEt₂)₂(NHex₂)]I and [C₃(NEt₂)₂(NHex₂)]OTf were also synthesized and characterized. The C₃h cations, [C₃(NMeR)₃]X (R = ethyl, allyl, -CH2CH2OCH₃ and phenyl, X = TFSA and DCA) were successfully prepared as well. The D₃h cation salts [C₃(NEt₂)₃]X (X = MeC6H4SO₃, OTf, I and F5C6O) and [C₃(NBu2)₃]X (X = B(CN)4 and FAP) were also prepared. The tac-based ILs [C₃(NEt₂)₃]+ and [C₃(NBu2)₃]+ were also complexed with metal halides - - 2- 2- forming salts with FeCl₄ , SnCl₃ , CuCl₄ and ZnCl₄ . Reaction of pentachlorocyclopropane (C₃Cl5H) with BuNH2 gave the open ring allylium product [H2C₃(NBuH)4]2+. This was characterized as Cl- and TFSA- salt. During the synthesis of [C₃(NMe₂)₃]Cl, the open ring cation [HC₃(NMe₂)4]+ was also isolated and was characterized as the TFSA- salt. XX Abstract The TGA, DSC, density, viscosity, conductivity, and molar conductivity properties for the ILs were measured where possible. The viscosity and conductivity data was fitted for the Arrhenius and Vogel-Fulcher Tamman equations. The entire tac-based ILs lie below the KCl ideal line in Walden plot. A fragility plot was obtained by fitting the viscosity data and all the tac-based ILs were fragile. The crystal structures of [C₃(NPhH)₃]TFSA, [C₃(NEt₂)₃]FeCl₄ and [HC₃(NMe₂)4]Cl.2CH₃Cl were determined

Decoupled ion mobility in nano-confined ionic plastic crystal

Nanoconfined ions have dramatically different local environments compared to the bulk, which profoundly affects the ion solvation and transport properties taking place in the confined space. Herein, we investigate the rotational and translation mobility of both cation and anions of an OIPC (diethyl)(methyl)(isobutyl)phosphonium hexafluorophosphate) confined in 40 and 180 nm straight-through Al2O3 pores. The results revealed that the nanoconfined OIPC exhibit 44 times higher ionic conductivity than the bulk material at 30 degrees C. This enhancement is attributed to both the reduced tortuosity and the increased population of mobile species. More interestingly, the Al2O3 nanochannels were found to selectively enhance the rotation and translational motion of [P-122i4] cation at elevated temperatures, whilst leaving that of the [PF6] anion less affectedM. F. thanks the Ikerbasque foundation for a visiting professorial fellowship. The authors acknowledge the Australian Research Council for funding through CE140100012. Deakin University's advanced characterisation facility is acknowledged for use of the NMR instruments, funded through the ARC grant LE110100141. J. M. thanks MCIU for the Ramon y Cajal contract and the grant Ref. PGC2018-094620-A-I00. Authors would like to thank the financial support provided by the IONBIKE RISE project. This project has received funding from the European Union's Horizon 2020 research and innovation programme under the Marie Skodowska-Curie grant agreement No. 82398