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In this manuscript, we report a detailed physico-chemical comparison between the α- and β-polymorphs of the NaMnO2 compound, a promising material for application in positive electrodes for secondary aprotic sodium batteries. In particular, the structure and vibrational properties, as well as electrochemical performance in sodium batteries, are compared to highlight differences and similarities. We exploit both laboratory techniques (Raman spectroscopy, electrochemical methods) and synchrotron radiation experiments (Fast-Fourier Transform Infrared spectroscopy, and X-ray diffraction). Notably the vibrational spectra of these phases are here reported for the first time in the literature as well as the detailed structural analysis from diffraction data. DFT+U calculations predict both phases to have similar electronic features, with structural parameters consistent with the experimental counterparts. The experimental evidence of antisite defects in the beta-phase between sodium and manganese ions is noticeable. Both polymorphs have been also tested in aprotic batteries by comparing the impact of different liquid electrolytes on the ability to de-intercalated/intercalate sodium ions. Overall, the monoclinic α-NaMnO2 shows larger reversible capacity exceeding 175 mAhg−1 at 10 mAg−1.

International audience; We investigate the effects of thermal treatments in vacuum or air on amorphous Ta 2 O 5 deposited on crystalline Si by Ion Beam Sputtering, mimicking the coatings of the mirrors of the gravitational-wave revealers of the Advanced Virgo and Advanced LIGO detectors. Argon is present in the whole thickness of the coating, likely introduced during the synthesis, and it can be released above 200°C in vacuum, while less discharge of Ar is detected during heating in air. Formation of sub-stoichiometric Ta oxides is evidenced in the surface layers, after in-vacuum annealing. The macroscopic structure of the samples is not affected by the thermal treatments. However, the length of the interference fringes, due to the coating, decreases after thermal treatments both in air and in vacuum, suggesting an increase of the Ta 2 O 5 thickness of ~1-2%, caused by an increase of the volume of the pores present in the structure.

The results of Fourier Transform Infrared absorption and Raman spectroscopy studies are reported for solid and liquid neat butane-1,4-diamine (DAB) and for the molecule in different solvents. Ab initio molecular dynamics and static calculations are reported in the work as an interpretative tool for the measurements and provide an analysis of the relative population of DAB conformers, both in vacuo and in the liquid phase. X-ray diffraction data for liquid DAB are presented to further consolidate the interpretation of the conformation and structure of the biomolecule in the liquid phase. The study of DAB in polar solutions suggests a high level of structuring of the molecules in the liquid, as a consequence of the effect of solvent on the molecular charge distribution.

International audience; In this work, Aliquat 336 ([Aliquat+]) based ionic liquids containing the fluorinated anion bis(trifluoromethylsulfonyl)imide [NTf2−] was successfully prepared by the anionic exchange replacement of the chloride anion. The reaction of lithium bis(trifluoromethylsulfonyl)imide with N-Methyl-N,N,N-trioctylammonium chloride ([N1,8,8,8][Cl] in water lead to the corresponding IL, namely ([Aliquat+][NTf2−]). The obtained ionic liquid was characterized by using infrared and Raman spectra and its structure was confirmed by 1H-NMR, 13C-NMR, and 19F-NMR. The thermal properties were investigated by two complementary thermal analysis techniques: TGA and DTA. A hexadentate coordination mode between cation-anion was predicted by atoms in molecules (AIM) studies for the [Aliquat+][NTf2−] IL by using B3LYP/6-31G* calculations where three O atoms of the anion in Cis conformation are linked to six H atoms of cation by S-O•••H interactions. Changes in the bond orders of S and O atoms of the cation supported such observations. The predicted cation-anion distances were in the range 2.30-2.60 Å. The harmonic force fields of cation and anion were calculated and the complete assignments were performed for both species while the most important bands observed in the infrared and Raman spectra of the IL were assigned. In addition, the scaled force constants of cation and anion of the IL were also reported.

Here we discuss the thermodynamics of the hydrolysis of four fluorinated lithium salts widely used in aprotic electrolytes for lithium-ion batteries: lithium hexafluorophosphate (LiPF6), lithium bis(trifluoromethylsulfoyl)imide (LiTFSI), lithium bis(fluorosulfonyl)imide (LiFSI) and the hybrid salt lithium fluorosulfonyl-trifluorofulfonyl imide (LiFTFSI). We performed density functional theory calculations at the B3LYP/6-31++G** level of theory using an implicit solvation model, to derive the electronic structures, vibrational properties and the thermodynamic stability of reagents, reaction intermediates and hydrolysis products. We combined ab initio thermodynamic evaluations in solution with thermochemical cycles to derive the variation of the Gibbs energy of heterogeneous reactions, where the precipitation of solid products is considered. Our analysis has been performed at three different temperatures to investigate the possible influence of the temperature on the formation of the reaction products. Overall, the use of imide-based anions limits the spontaneous hydrolysis, by hindering the formation of POF3 differently from LiPF6. All FSI- TFSI- and FTFSI-hydrolyses lead to the precipitation of solid LiOH and, to a lesser extent, of solid LiF. In comparison with other salts, LiTFSI apparently holds down more efficiently the precipitation of solid LiF and limits the onset of the self-feeding salt degradation mechanisms.

International audience; Egg shell (ES) is a biological macromolecule mainly containing calcite embedded in proteins and polysaccharides, while shell membrane predominantly contains proteins. Thus ES with membrane (ESM) possesses richer protein contents than ES. In the present work, ES and ESM have been separately modified using mono-and di-cationic imidazolium ionic liquids, [C 5 mim + ][Br-] (IL) and [Bis-(PhCH 2 MIm) + ][2Cl-] (DIL). Thus four modified products have been obtained namely ES-IL, ES-DIL, ESM-IL and ESM-DIL. In order to determine physico-chemical modifications of the ES due to the interactions with the ionic liquids, the structural, spectroscopic and thermal properties of all products were investigated by means of XRD, FTIR and TG/DTA. The IR spectra display significant changes in the 1400-1550 and 2800-3100 cm-1 regions confirming the insertion of IL and DIL into the ES and ESM layers. Furthermore, the XRD results indicate that this modification process influence the crystal structure of the ES. Thermal analysis suggests that the chemical modification increases the thermal stability of the ES and ESM. It has also been ascertained that presence of proteins in the shell membrane is responsible for increasing thermal stability in the order ES < ESM < ES-IL < ESM-IL < ES-DIL < ESM-DIL.

Knowledge of all the intermolecular forces occurring in ionic liquids (ILs) is essential to master their properties. Aiming at investigating the weaker hydrogen bonding in aprotic liquids, the present work combined computational study and far-infrared spectroscopy on four imidazolium-based ILs with different anions. The DFT calculations of the ionic couples, using the ωB97X-D functional and considering both the empirical dispersion corrections and the presence of a polar solvent, show that, for all samples, the lowest energy configurations of the ion pair present H atoms, directly bound to C atoms of the cation and close to O atoms of the anion, capable of creating moderate to weak hydrogen bonding with anions. For the liquids containing anions of higher bonding ability, the absorption curves generated from the calculated vibrational frequencies and intensities show absorption bands between 100 and 125 cm−1 corresponding to the stretching of the hydrogen bond. These indications are in complete agreement with the presently reported temperature dependence of the far-infrared spectrum, where the stretching modes of the hydrogen bonding are detected only for samples presenting a moderate interaction and become particularly prominent at low temperatures. Moreover, from the analysis of the infrared spectra, the occurrence of various phase transitions as a function of temperature was detected, and the difference in the average energy between the H-bonded and the dispersion-governed molecular configurations was evaluated.

International audience; Through N-alkylation of 1,4-diazabicyclo [2.2.2] octane with 1-bromooctane a new ionic liquid, namely 1‐octyl‐1,4‐diazabicyclo [2.2.2] octan‐1‐ium Bromide [C8DABCO+][Br−] has been synthesized and characterized by FT-IR, FT-Raman and by 1H and 13C-NMR spectroscopies. Three ionic C-H...Br bonds were predicted by natural bond orbital (NBO), atoms in molecules (AIM) calculations and bond orders but a monodentate coordination between cation and anion is suggested because only one of them has higher energy and lower distance. The effect of Br on properties of IL is clearly observed by the change in orientation and direction of dipole moment vector in the IL, as compared with the cation. NBO studies reveal that the Br anion strongly stabilizes to cation to form the IL. The complete vibrational assignments of 129 and 132 vibration modes expected for the cation and its IL were performed by using two harmonic force fields with the SQMFF methodology and transferable scaling factors. The scaled harmonic force constants were also reported for both species. The Br confers a higher reactivity to [C8DABCO+][Br−], as suggested by analyses of frontier orbitals. Reasonable correlations were found between the experimental IR, Raman and NMR spectra and the corresponding theoretical ones.

The effects induced by alkyl chain length on the thermal phase behavior for a series of imidazolium based ionic liquids (ILs) containing the anion bis(trifluoromethanesulfonyl)imide (TFSI) were investigated by infrared spectroscopy combined with density functional theory (DFT) calculations. In agreement with previous results on pyrrolidinium and ammonium based ionic liquids sharing the TFSI anion, our study shows that with increasing the length of the alky chain only the less stable cis-TFSI is retained in the solid state, while for shorter chain the trans-TFSI predominates in the crystalline phase. Also, we examined the remarkable effect on the packing efficiency due to the addition of 2-hydroxyethyl group on the imidazolium cation ring, reporting that the absence of crystallization is observed in correspondence with the presence of both the conformers of TFSI in the whole temperature range (150–325 K). Moreover, a detailed study of 1-ethyl-2,3-dimethylimidazolium-TFSI (EDMIM-TFSI) reveals the existence of cation rotational isomerism. In the liquid phase both planar (P) and non-planar (Np) conformers are present in the equilibrium, while a conformational change for the CNCC dihedral angle of the EDMIM cation leads to stabilize the formation of the more stable non-planar geometry in the crystalline phase.

In this paper, a new ionic liquid; [C8DABCO+][PF6-] was prepared, its structure was well confirmed by 1H, 13C, 19F and 31P-NMR spectroscopies. Besides, thermal behaviour has been discussed through TGA and DTA in the temperature range from [-80 to 200 °C] and [25 to 700 °C] respectively. Theoretical studies were performed by DFT method to investigate the structural, electronic and topological properties. B3LYP/6-31G* calculations support the high solvation energy value of IL in aqueous solution (?Gc= -122.9 kJ/mol) and it probably explain the high dipole moment value, the volume expansion in this medium (7.3 Å3) and also because the cation-anion interactions still remain in solution. Seven interactions were predicted by AIM calculations but only two cation-anion interactions have short distances. NBO studies reveal that IL is more stable in solution probably due to its higher solvation energy. The DOS spectrum in aqueous solution shows clearly that the orbitals belonging to the atoms of cage-like DABCO structure participle in both HOMO and LUMO and, hence, will confirm that DABCO is engaged in halogen interactions, as suggested from NBO analyses. These studies show that DABCO structure participates in the properties of [C8DABCO+][PF6-]. Complete assignments of IR and Raman spectra were reported

The chromium terephthalate MIL-101 is a mesoporous metal-organic framework (MOF) with unprecedented adsorption capacities due to the presence of giant pores. The application of an external pressure can effectively modify the open structure of MOFs and its interaction with guest molecules. In this work, we study MIL-101 under pressure by synchrotron X-ray diffraction and infrared (IR) spectroscopy with several pressure transmitting media (PTM). Our experimental results clearly show that when a solid medium as NaCl is employed, an irreversible amorphization of the empty structure occurs at about 0.4 GPa. Using a fluid PTM, as Nujol or high-viscosity silicone oil, results in a slight lattice expansion and a strong modification of the peak frequency and shape of the MOF hydroxyl vibration below 0.1 GPa. Moreover, the framework stability is enhanced under pressure with the amorphization onset shifted to about 7 GPa. This coherent set of results points out the insertion of the fluid inside the MIL-101 pores. Above 7 GPa, concomitantly to the nucleation of the amorphous phase, we observe a peculiar medium-dependent lattice expansion. The behavior of the OH stretching vibrations under pressure is profoundly affected by the presence of the guest fluid, showing that OH bonds are sensitive vibrational probes of the host-guest interactions. The present study demonstrates that even a polydimethylsiloxane silicone oil, although highly viscous, can be effectively inserted into the MIL-101 pores at a pressure below 0.2 GPa. High pressure can thus promote the incorporation of large polymers in mesoporous MOFs.

The infrared absorbance spectrum of the ionic liquid 1-butyl-1-methylpyrrolidinium dicyanamide, mixed with water at two different concentrations, was measured between 160 and 300K in the mid infrared range. Both mixtures do not crystallize on cooling, however, remarkably, the one with an ionic liquid (IL):water composition of 1:3 displays a cold crystallization process on heating in a restricted temperature range between 240 and 250K. A portion of the water participates to the cold crystallization. On the contrary, with an IL:water composition of 1:6.6 no crystallization takes place. Upon water addition the vibration frequencies of the anion and of some lines of the cation are blue shifted, while the absorption lines of water are red shifted. These facts are interpreted as the evidence of the occurrence of the hydrogen bonding of water, as the hydrogen bonding acceptor with respect to the anion (anion∙∙∙O-H bonds develop) and as hydrogen donor for the cation (C-H∙∙∙O bonds can form). Microscopic inhomogeneities in the samples and their evolution with temperature are discussed.

The infrared absorption spectrum of 1-ethyl-3-methylimidazolium trifluoromethanesulfonate (EMI&ndash, TfO) was investigated at ambient pressure and variable temperatures between 120 and 330 K, or at room temperature and variable pressures up to 10 GPa. Upon cooling, the ionic liquid crystallizes, on the contrary, upon compression no evidence of crystallization can be obtained from the infrared spectra. Moreover, Density Functional Theory (DFT) calculations were applied to gain a better description of the ionic couple. The &omega, B97X-D functional, including not only the empirical dispersion corrections but also the presence of a polar solvent, gives a good agreement with the infrared spectrum and suggests that TfO resides above the plane of the imidazolium, with the shorter distance between the O atom of the anion and the C2 atom of the imidazolium ring equal to 2.23 &Aring

Transition metal substitution is a key strategy to optimize the functional properties of advanced crystalline materials used as positive electrodes in secondary lithium batteries (LIBs). Here we investigate the structural alterations in the olivine lattice of Mn and Ni substituted LiCoPO4 phase and the impact on performance in LIBs. X-ray diffraction (XRD) and extended X-ray absorption experiments have been carried out in order to highlight the structural alterations induced by partial substitution of cobalt by manganese and nickel. XRD analysis suggests that substitution induces an expansion of the lattices and an increase of the antisite disorder between lithium and transition metal ions in the structure. XAS data highlight negligible electronic disorder but a relevant modulation in the local coordination around the different metal ions. Moreover, galvanostatic tests showed poor reversibility of the redox reaction compared to the pure LCP sample, and this failure is discussed in detail in view of the observed remarkable structural changes.

International audience; The [Aliquat+][Cl−] ionic liquid (IL) has been structural and vibrationally characterized combining experimental FT-IR, FT-Raman and 1H- and 13C-NMR spectroscopies with theoretical studies based on the hybrid B3LYP/6-31G* method. The theoretical determination of structure of IL in gas phase and aqueous solution by using that level of theory shows three ionic C-H···Cl bonds, as supported by atomic Merz-Kollman (MK) charges, bond orders, natural bond orbital (NBO) and atoms in molecules (AIM) calculations. Hence, a monodentate coordination between the [Aliquat+] cation and Cl anion has been proposed for IL because only one of three ionic C-H···Cl bonds presents higher energy and lower distance. The optimized structure confirmed by NMR measurements has allowed the assignments of 237 normal vibration modes to the bands observed in the infrared and Raman spectra with the aid of scaled quantum mechanical force field (SQMFF) methodology and the normal internal coordinates. The effect of Cl in the IL is the shifting of vibration modes corresponding to the CH2 and CH3 groups, as compared with the cation. The mapped MEP surface evidence a strong concentration of charges around the chloride anion compatible with nucleophilic sites in these regions while the frontier orbital analyses suggest that IL is most reactive than the cation probably due to the low values of both global electrophilicity and nucleophilicity indexes. The thermal stability shows that [Aliquat+][Cl−] start to decompose just above 200°C. Comparisons between [Aliquat+][Cl−] and [Aliquat+][NTf2−] ILs show that the IL containing chloride is most reactive than the other one while [Aliquat+] [NTf2−] is thermally more stable than [Aliquat+][Cl−]. These results suggest that the properties of an IL containing the [Aliquat+] cation are strongly dependent of anion. In addition, the scaled force constants for the [Aliquat+][Cl−] IL are also calculated and compared with the reported for the cation. The Cl anion modifies in notable form the properties of cation.

In the last 20 years, the research on amorphous metal alloys has led to the development of materials with selective hydrogen permeabilities that are comparable or even higher than those of palladium and palladium alloys. The most promising materials are composed of Ni, Nb, Zr, with the possible addition of Ta or Ti. The operating temperatures are found to be in the range 300–400°C, in order to avoid the crystallization that usually occurs at higher temperatures, as a multistep process. The solubility and permeability have been investigated experimentally and computational modeling for prescreening of properties in a large variety of materials have been proposed. Good correspondence has been found with experiments, where available. There are experimental and computational modeling reports available on the mechanical properties of these amorphous ribbon membranes regarding to their resistance to hydrogen embrittlement. Microstructural correlation of these ribbon membranes with the local atomic order have emerged.

The Protic Ionic Liquid (PIL) formed by neutralization of the super-strong base 1,7-diazabicyclo[5.4.0]undec-7-ene (DBU) with the super-strong acid bis(trifluoromethanesulfonyl)-imide (TFSI), indicated as [DBUH][TFSI], has been investigated. Its chemical physical properties and structural features have been explored using a synergy of experimental and computational tools. Molecular Dynamics-rationalised X-ray diffraction patterns highlight the major role played by hydrogen bonding (HB) in affecting morphology in this PIL. A comparison between HB features in this and in related PILs has been presented, on the base of far-IR experiments and DFT analysis. Indications of a weaker HB interaction in [DBUH][TFSI] in comparison with [DBUH][TfO], consistently with their ΔpKa difference, have been observed and rationalised in terms of geometrical properties of the main conformers contributing to the experimental spectra. In the liquid phase of [DBUH][TFSI] a particularly large conformational disorder is observed and the corresponding large dispersion of the frequencies of the HB stretching modes leads to a broad absorption band without a well defined peak. On the contrary, well detectable HB related absorptions are observable in the solid phase of [DBUH][TFSI] and at all temperatures in [DBU][TfO], where less configurational disorder occurs.

The X-ray scattering patterns of the two ionic liquids, N-trimethyl-N-propylammonium bis(trifluoromethanesulfonyl)imide (TMPA-TFSI) and N-trimethyl-N-hexylammonium bis(trifluoromethanesulfonyl)imide (TMHA-TFSI), sharing a common anion and differing in the length of the alkyl chain of the cation, were measured at room temperature. Molecular dynamics calculations supported the interpretation of the data. The two force-field models, GAFF and DLPOLY 4, were adopted to simulate the scattering patterns. Both of them are able to reproduce the main peaks of the experimental data; however, the DLPOLY model seems to better reproduce the finer details. Moreover, from the simulations, the concentration of the two conformers of TFSI are derived. The comparison with previously reported infrared spectroscopy measurements suggests that also under this aspect the DPOLY model has a better agreement with the experiments.

In this study, a new para‑xylyl linked di‑imidazolium [p‑C6H4(CH2ImMe)2+] ionic liquid (DIL) containing the bis(trifluoromethanesulfonyl)imide [(CF3SO2)2N−] anion is synthesized. The method is based on the alkylation reaction of 1‑methyl imidazole, followed by anion exchange. The obtained DIL is characterized by 1H NMR, 13C NMR, 19F NMR and FT-IR spectroscopy. The melting point and the subsequent decomposition of [p‑C6H4(CH2ImMe)2+][(CF3SO2)2N−]2 are measured by using differential scanning calorimetry (DSC) and thermogravimetric (TGA) analyses in the temperature range from 25 to 700 °C. Thermal analysis indicated that this DIL melted below 100 °C and can, therefore, be classified as an ionic liquid. Vibrational spectroscopy studies were conducted by infrared (IR), Raman (FT-Raman) spectroscopy and DFT calculations. Moreover, the crystal structure is investigated by single crystal X-ray diffraction (XRD) method. The X-ray studies on [p‑C6H4(CH2ImMe)2+][(CF3SO2)2N−]2 show that it crystallizes in the monoclinic system with space group P21/c. The theoretical structural parameters such as bond lengths, bond angles and dihedral angles determined by DFT methods are in good agreement with the XRD results.

An alloy with nominal composition V85Ni15 was prepared in a vacuum induction melting apparatus. The chemical analysis of the sample showed a V (Ni) content of 82.63 (15.68) at% and small contaminations by carbon and aluminum. XRD measurements confirmed that the bcc Ni-V solid solution phase is the main constituent of the sample. However, a minor impurity (approximately 6.5 wt%) due to the precipitation of the sigma NiV3-x phase is present in the sample. Hydrogen sorption measurements extending from 150 °C up to 400 °C in a wide pressure range (up to 90 bar) were performed. Upon hydrogenation below 250 °C, one observes the subsequent presence of an α phase and of two hydride phases with different values of dehydrogenation enthalpy: ΔHdehydr = 21 ± 1 kJ/mol for 0.15 ≤ H/M ≤ 0.30 and ΔHdehydr = 26 ± 2 kJ/mol for 0.53 ≤ H/M ≤ 0.59. Above 300 °C, there is no evidence of the formation of hydrides and only an α phase is present up to the maximum measured composition, with a hydrogenation enthalpy ΔHhydr = 10.0 ± 0.5 kJ/mol.

The effect of ether-functionalisation on ionic liquids (ILs) is discussed based on Kamlet-Taft parameters and the infrared (IR) spectra of N-ethoxyethyl-N-methylpiperidinium bis(trifluoromethanesulfonyl)imide ([P1,2O2][TFSI]) and N-ethoxyethyl-N-methylmorpholinium bis(trifluoromethanesulfonyl)imide ([M1,2O2][TFSI]). The results are analysed taking into consideration their ion conformers, electronegativity and hardness, and the IR active vibrations obtained by means of DFT calculations. From the evaluation of Kamlet-Taft parameters, the ether-functionalisation in the cationic ring is found to improve the polarity and hydrogen bond acidity of the ILs. This correlates with the computational result which designates that the oxygen atom in the cationic ring increases the electronegativity of the cation. The comparison with the IR spectra, which were obtained experimentally and computationally, revealed that trans-[TFSI] was preferably formed in [M1,2O2][TFSI] compared to [P1,2O2][TFSI]. Although the Kamlet-Taft parameters indicate that [M1,2O2][TFSI] has a higher polarity, this IL preferably adopts trans-[TFSI], which is normally stabilised with the cations having a lower polarity. This may be due to the presence of the oxygen in the cationic ring which delocalises the electron density of the lowest unoccupied molecular orbitals (LUMO) and increases the conformational freedom of the hydrogen bonds between cations and anions. Moreover, the mixtures of pure ILs with a suitable Li-salt were also investigated to analyze the effect of the Li salt on the polarity and the ion conformers.

Ni based amorphous materials have great potential as hydrogen purification membranes. In the present work the melt spun (Ni0.6Nb0.4−yTay)100−xZrx with y=0, 0.1 and x=20, 30 was studied. The result of X-ray diffraction spectra of the ribbons showed an amorphous nature of the alloys. Heating these ribbons below T

Alanates have recently attracted attention as new anodic materials for lithium ion batteries. The electrochemical activity of sodium alanate has been already reported and the conversion mechanism explained. Through a complex conversion reaction, this compound is able to develop almost all the theoretical capacity, achieving more than 1700 mAh/g upon first discharge with an efficiency of 70%. Nevertheless alanate undergoes to capacity fade in few cycles. This is mainly due to the severe structural reorganization following the conversion reaction, that results in electrode pulverization and loss of electric contact. Here, we present a nanocomposite material consisting of NaAlH4 confined in the nanoporous of a carbon matrix able to mitigate the effect of volume expansion and improve the cyclability. Specifically, the nanocomposite has been studied in terms of structure, morphology and hydrogen content by the means of Infrared Spectroscopy, solid state NMR, electronic microscopy and thermal analysis. Finally, its performance in lithium cells is presented. © 2017 The Electrochemical Society. All rights reserved.

A composite membrane based on a Nafion polymer matrix incorporating a non-stoichiometric calcium titanium oxide (CaTiO3&minus, &delta, ) additive was synthesized and characterized by means of thermal analysis, dynamic mechanical analysis, and broadband dielectric spectroscopy at different filler contents, namely two concentrations of 5 and 10 wt.% of the CaTiO3&minus, additive, with respect to the dry Nafion content, were considered. The membrane with the lower amount of additive displayed the highest water affinity and the highest conductivity, indicating that a too-high dose of additive can be detrimental for these particular properties. The mechanical properties of the composite membranes are similar to those of the plain Nafion membrane and are even slightly improved by the filler addition. These findings indicate that perovskite oxides can be useful as a water-retention and reinforcing additive in low-humidity proton-exchange membranes.

The pressure-composition isotherms and the absorption kinetics of both hydrogen and deuterium were investigated for an amorphous membrane, potentially useful for hydrogen purification and separation in membrane reactors, with atomic composition Ni32Nb28Zr30Cu10. In the temperature range between 294 and 394 °C, the equilibrium pressure between the gas and the solid was higher for deuterium than for hydrogen, with a typical ratio P(D2)/P(H2)≈1.5. Moreover, the absorption of H2 is faster than that of D2. Both behaviors of the presently investigated amorphous membrane closely resemble those of the Pd–Ag alloys, that are currently used in membrane reactors and separators.

Platinum scarcity and its high cost have led to the requirement of alternative materials catalysing the oxygen reduction reaction (ORR), which is the main rate-determining step occurring in electrochemical devices, including metal-air batteries and fuel cells. We report a study on a sub-stoichiometric calcium titanate (CaTiO3-?, CTO) compound used as promoter for the ORR in order to reduce the Pt loading and improve its electrocatalytic activity. Composite catalysts based on Pt/C with different amounts of CTO were prepared and their activity was investigated by rotating disk electrode (RDE). The obtained results proved a higher catalytic activity for the composite electrode, with respect to pure Pt/C, in terms of electrochemically active surface area, oxygen reduction current density, onset potential and stability

The infrared absorption spectrum of amorphous Mg(B 3 H 8 ) 2 (THF) 2 was measured in the mid-infrared region between 600 and 3300 cm −1 . In the frequency range corresponding to B–H stretching vibrations, the observation of absorptions due to the movements of Mg–H–B bridging hydrides provides evidence of direct bond between octahydrotriborate ions and magnesium. Starting from this configuration, DFT and ab-initio calculations at the MP2, B3LYP and B97D level were utilized in order to find the lowest energy geometry of the Mg(B 3 H 8 ) 2 (THF) 2 complex. The results of all the computational studies indicate that the interaction of Mg with the [B 3 H 8 ] − ions entails two B–Mg and two B–H–Mg bonds. The calculated infrared absorptions closely reproduce the experimental spectrum. Moreover, calculations provide evidence of the stabilization of the THF solvate of Mg(B 3 H 8 ) 2 and indicate that the THF complex has a greater stabilization energy than dialkyl ethers complexes by ∼25 kJ/mol.

A detailed Raman study has been carried out on the ionic liquid 1-butyl-1-methylpyrrolidinium bis(trifluoromethanesulfonyl)imide (PYR14-TFSI) over a wide pressure (0-8 GPa) and temperature (100-300 K) range. The explored thermodynamic region allowed us to study the evolution of the system across different solid and liquid phases. Calculated Raman spectra remarkably helped in the spectral data analysis. In particular, the pressure behavior of the most intense Raman peak and the shape analysis of the ruby fluorescence (used as a local pressure gauge) allowed us to identify a liquid-solid transition around 2.2 GPa at T = 300 K. The low-frequency Raman signal as well as the absence of remarkable spectral shape modifications on crossing the above threshold and the comparison with the spectra of the crystalline phase suggest a glassy nature of the high-pressure phase. A detailed analysis of the pressure dependence of the relative concentration of two conformers of TFSI allowed us to obtain an estimate of the volume variation between trans-TFSI and the smaller cis-TFSI, which is the favored configuration on applying the pressure. Finally, the combined use of both visual inspection and Raman spectroscopy confirmed the peculiar sequence of phase transitions observed as a function of temperature at ambient pressure and the different spectral/morphological characteristics of the two crystalline phases.

We report a systematic investigation of the far- and mid-infrared spectra of ionic liquids (ILs) containing the bis(fluorosulfonyl)imide (FSI) anion, both in the liquid state at room temperature and in solid phases at low temperatures. We extended to lower frequencies a previous study, and we observed four additional vibration bands below 500 cm −1 , attributable to FSI. Moreover, DFT calculations of vibration frequencies were performed using three combinations of theory and basis set: (1) B3LYP/6-31G**, (2) B3LYP/6-311 + G(3df) and (3) PBE0/6-31G**. Model 1, largely used in the previous literature concerning ILs, shows the poorest performances; model 2, which generally gives a good agreement with the experiments, misses the vibration frequencies by ∼40 cm −1 in the range 650–900 cm −1 where one finds the largest spectral differences between cis - and trans -FSI; model 3 gives the best agreement with the experiments and, moreover, is much less time consuming than model 2. The comparison with calculations suggests that the band centered around 1217 cm −1 is a good marker of the occurrence of the cis -FSI conformer. Finally, the bands located around 730 and 750 cm −1 are attributable to cis - and trans - conformer of FSI, respectively.

Two new di-cationic imidazolium based ionic liquids (ILs) containing chloride, (bisImCl), or hexafluorophosphate anions (bisImPF6) have been synthesized and characterized by FT-Raman and 1H- and 13C NMR spectroscopies. The p-xylyl group acts a spacer between two imidazolium rings in the cation. The influence of the anions on thermal properties of the compounds has been investigated. Both bisImCl and bisImPF6 have shown good thermal stability up to at least 280 °C. Intermolecular and cation-anion interactions have been investigated by NMR spectroscopy. B3LYP/6-311++G∗∗ calculations have optimized the structure of bisIm cation with both anions. Both Cl are found to be in a monodentate coordination, while in bisImPF6 only one PF6 group presents monodentate coordination. AIM calculations at the same level of theory have evidenced a higher number of interactions in bisImPF6, as compared to bisImCl. A complete assignment of the vibrational frequencies for the cation, bisImCl and bisImPF6 are here reported together with a set of harmonic scaled force constants calculated for the cation and bisImCl. Further, polarizability (α) and the static first hyperpolarizabilities (β) of these ILs are calculated by different DFT functionals in order to understand nonlinear optical (NLO) properties. It is observed an inverse correlation between the predicted β value and the HOMO-LUMO energy difference (Δe) from two state models. The high gap value observed for bisImPF6 justifies its low reactivity, as supported by the high number of interactions predicted for this ionic liquid.

Three new substituted dicationic ionic liquids (DILs) based on biphenylenedimethylene linked bis-1-methylimidazolium ionic liquids [bis-(PhCH2MIm)+], combined with three anions, namely dichloride [Cl]2, di (hexafluorophosphate) [PF6−]2 and di(bis(trifluoromethylsulfonyl)Imide) [(CF3SO2)2N−]2 were synthesized. The three synthesized dicationic ionic liquids were characterized by Nuclear Magnetic Resonance and Fourier transform infrared (FTIR) and Raman spectroscopy in the region 4000–600 cm−1 and 4000–45 cm−1, respectively. A complete vibrational assignments have been performed; the biphenylene linkage spacer is confirmed by the presence of strong Raman band at 1616 cm−1 related to the C=C vibration in all our investigated DILs. Moreover, a conformational investigation of the cation was performed by means of DFT calculations using the 6 31G∗∗ basis set and the B3LYP theory. The comparison of the computed and experimental Raman spectra further corroborate the structure of the cation. Finally, the thermal stability of the DILs was investigated by TGA and DTA measurements. The DILs with Cl−, PF6− and [(CF3SO2)2N−] anions decompose at 252, 323 and 420 °C, respectively.

Experimental attenuated total reflectance (ATR) and Raman spectra for the synthesized ionic liquid 1-Ethyl-3-methylimidazolium hexafluorophosphate [EMIM+][PF6−] have been combined with the functional hybrid B3LYP and the 6-31G∗ and 6-311++G∗∗ basis sets in order to evaluate the coordination mode of [PF6−] anion and determine the its structural, electronic, topological and vibrational properties. The scaled quantum mechanical force fields (SQMFF) methodology allowed us to obtain a set of scaled force constants fitting the observed wavenumbers because, so far, they have not reported. Experimental ATR and Raman spectra for the ionic liquid [EMIM+][PF6−] in the solid phase are consistent with the corresponding predicted by using both levels of theory. Here, complete vibrational assignments of 72 normal modes of vibration expected for ionic liquid were performed by using B3LYP/6-311++G∗∗ level and considering that the [PF6−] anion adopts a bidentate coordination mode. Atomic Merz-Kollman (MK) charges and bond orders studies have revealed a distorted octahedral symmetry of anion in the ionic liquid and have suggested bidentate coordination of anion by two C–H⋯F hydrogen bonds, as experimentally was also proposed. Natural bond orbital (NBO) and atoms in molecules (AIM) calculations support the high stability of ionic liquid and its high dipole moment value. Frontier orbitals for the three species show that the [PF6−] anion increases the reactivity of ionic liquid. Here, we determine that the B3LYP/6-311++G∗∗ molecular force field for the ionic liquid [EMIM+][PF6−] with the bidentate coordination mode adopted by [PF6−] anion is well represented, as also was supported by the scaled force constants calculated for both C–H⋯F hydrogen bonds.

Several recent studies of hydroxyl-functionalized ionic liquids (ILs) have shown that cation-cation interactions can be dominating these materials at the molecular level when the anion involved is weakly interacting. The hydrogen bonds between the like ions led to the formation of interesting chain-like, ring-like, or distinct dimeric (i. e. two ion pairs) supermolecular clusters. In the present work, vibrational spectroscopy (ATR-IR and Raman) and density functional theory (DFT) calculations of the hydroxyl-functionalized imidazolium ionic liquid C 2 OHmimCl indicate that anion-cation hydrogen bonding interactions are dominating, leading to the formation of distinct dimeric ion pair clusters. In this arrangement, the Cl - anions function as a bridge between the cations by establishing bifurcated hydrogen bonds with the OH group of one cation and the C(2)-H of another cation. Cation-cation interactions, on the other hand, do not play a significant role in the observed clusters.

The anelastic spectrum of the N-butyl-N-methyl-pyrrolidinium (trifluoromethanesulfonyl) (nonafluorobutanesulfonyl)imide (PYR14-IM14) is reported for the first time. On cooling, at 4 Kmin-1 the sample undergoes a glass transition around 190 K. In the liquid phase, a thermally activated relaxation process is measured and it is analyzed by means of a modified Debye model. The best fit results indicate that the peak is related to the ion hopping between non-equivalent configurations which are mainly defined by the anion conformer configuration. © 2018 Universidade Federal de Sao Carlos. All rights reserved.

The chemical and physical properties of imidazolium-based ionic liquids are determined by the interactions between the counter-ions. The C(2) position plays an important role in these interactions, as it represents the predominant site for interionic hydrogen bonding. This study shows that the directional hydrogen bonds between highly symmetrical anions (iodide, tetrafluoroborate, hexafluorophosphate) and the C(2)-H group of the 1-methyl-3-propylimidazolium cation determine the molecular and macroscopic behavior in terms of the thermal properties. Upon replacing the C(2) proton by a methyl group, the anion repositions itself at the C(4)/(5) moiety, where it forms a new hydrogen bond, apparently with only one of the two CH groups. In addition, the larger the anion is in diameter, the more likely it will establish further interactions with other parts of the cation, such as the propyl chain.

Magnesium hydride has been proposed as innovative anode material for Li ion cells due to its large theoretical capacity and high-energy efficiency compared to other conversion materials. In this work, we report a combined experimental-theoretical study about the origin of voltage hysteresis in the conversion reaction of MgH2 in lithium cells. Experimentally, the extent of the thermodynamic voltage hysteresis in the first galvanostatic discharge-charge cycle has been determined by the GITT technique and decoupled from the kinetic overpotentials. Theoretically, the origin of the thermodynamic voltage hysteresis has been evaluated and studied by means density functional theory calculations within the supercell approach. Different elementary reactions have been modeled upon reduction and oxidation on the surfaces of the active phases (i.e., MgH2, LiH, and Mg), and the associated theoretical voltages have been predicted. Experimental and theoretical results have been compared and discussed to draw a comprehensive description of the elementary surface reactions of the MgH2 conversion in lithium cells. © 2015 American Chemical Society.

Amorphous (Ni0.6Nb0.4)1-xZrx membranes were investigated by means of X-ray diffraction, thermogravimetry, differential thermal analysis and tensile modulus measurements. Crystallization occurs only above 673 K, and even after hydrogenation the membranes retain their mainly amorphous nature. However, after exposure to gaseous hydrogen, the temperature dependence of the tensile modulus, M, displays large variations. The modulus of the hydrogen reacted membrane is higher with respect to the pristine samples in the temperature range between 298 K and 423 K. Moreover, a sharp drop in M is observed upon heating to approximately 473 K, well below the glass transition temperature of these glasses. We propose that the changes in the moduli as a function of temperature on the hydrogenated samples are due to the formation of nanocrystalline phases of Zr hydrides in (Ni0.6Nb0.4)1-xZrx-H membanes.

Here we report the synthesis at low temperature (220 °C) by a solvothermal method of highly crystalline LiCoPO 4 . This material is a candidate for application as cathode in next-generation Li-ion cells. The presented synthetic route allows a careful tailoring of the sample morphology and leads to morphologically homogeneous platelet-like particles. The obtained material has been characterized by synchrotron radiation X-ray diffraction, vibrational spectroscopies, X-ray photoemission spectroscopy and electron microscopies. The synthesized material has been also characterized in lithium cells to highlight its ability to reversibly cycle lithium.

In this work we present our recent results on three ionic liquids (ILs), which share bis(trifluoromethanesulfonyl)imide (TFSI) as anion and have different pyrrolidinium based cations. By means of a combination of mechanical spectroscopy and thermal analysis, many of the physical processes occurring during cooling down from the liquid phase, can be studied. Depending both on the diverse cation and the different thermal history, crystallization from the melt or glass transition, cold-crystallization, solid-solid phase transitions and thermally activated processes are observed. In one of the ILs, which could be easily undercooled, a prominent thermally activated peak could be observed above the glass transition. The temperature dependence of the relaxation time is approximated by a Vogel-Fulcher-Tamman equation, as usual for fragile glass forming liquids, and the apparent activation energy of W = 0.36 eV with a pre-exponential factor of the relaxation time τ0 = 1.7 · 10−13s were derived supposing jumps between asymmetrical potential wells. The kinetics of the crystallization processes have been studied in the framework of the Johnson-Mehl-Avrami-Kolmogorov theory and the Avrami parameters have been derived for both the crystallization from the melt and for the cold crystallization observed on heating.

Amorphous (Ni 0.6 Nb 0.4 ) 1−x Zr x membranes were investigated by means of X-ray diffraction, thermogravimetry, differential thermal analysis and tensile modulus measurements. Crystallization occurs only above 673 K, and even after hydrogenation the membranes retain their mainly amorphous nature. However, after exposure to gaseous hydrogen, the temperature dependence of the tensile modulus, M, displays large variations. The modulus of the hydrogen reacted membrane is higher with respect to the pristine samples in the temperature range between 298 K and 423 K. Moreover, a sharp drop in M is observed upon heating to approximately 473 K, well below the glass transition temperature of these glasses. We propose that the changes in the moduli as a function of temperature on the hydrogenated samples are due to the formation of nanocrystalline phases of Zr hydrides in (Ni 0.6 Nb 0.4 ) 1−x Zr x -H membanes.

In this study, two ionic liquids containing the bis(trifluoromethanesulfonyl)imide ( $$[(\hbox {CF}_{3}\hbox {SO}_{2})_{2}\hbox {N}^{-}]$$ ) anion are synthesized. The syntheses are based on an alkylation reaction of 1-methyl imidazole and 1,2-dimethyl imidazole followed by anion exchange. The obtained ILs are characterized by $$^{1}\hbox {H-NMR}$$ , $$^{13}\hbox {C-NMR}$$ , $$^{19}\hbox {F-NMR}$$ and FT-IR spectroscopy. Vibrational spectroscopy studies were conducted by infrared (FTIR/ATR), Raman spectroscopy and DFT calculations. The presence of methylation in the C2 position gives rise to specific marker bands in the Raman and IR spectra. In order to ascertain whether cation conformers are present in our ionic liquids, a computational study was performed using the density functional theory. The comparison of the experimental data and the computed spectra shows that three conformers of the imidazolium ions are present in both ionic liquids. Synopsis We synthesized and investigated the vibrational properties of two ionic liquids, namely, 1-methyl,3-propyl imidazolium bis(trifluoromethane-sulfonyl) imide ( $$[1\hbox {-MPrIM}^{+}][(\hbox {CF}_{3}\hbox {SO}_{2})_{2}\hbox {N}^{-}]$$ ) and 1,2-dimethyl,3-propyl imidazolium bis(trifluoromethane-sulfonyl) imide ( $$[1,2\hbox {-DMPrIM}^{+}][(\hbox {CF}_{3}\hbox {SO}_{2})_{2}\hbox {N}^{-}]$$ ). Methylation in the C2 position gives rise to specific marker bands in the Raman and IR spectra. The comparison of the experimental data and the computed spectra at DFT level shows that three conformers of the imidazolium ions are present in both ionic liquids.

Automotive and stationary energy storage are among the most recently-proposed and still unfulfilled applications for lithium ion devices. Higher energy, power and superior safety standards, well beyond the present state of the art, are actually required to extend the Li-ion battery market to these challenging fields, but such a goal can only be achieved by the development of new materials with improved performances. Focusing on the negative electrode materials, alloying and conversion chemistries have been widely explored in the last decade to circumvent the main weakness of the intercalation processes: the limitation in capacity to one or at most two lithium atoms per host formula unit. Among all of the many proposed conversion chemistries, hydrides have been proposed and investigated since 2008. In lithium cells, these materials undergo a conversion reaction that gives metallic nanoparticles surrounded by an amorphous matrix of LiH. Among all of the reported conversion materials, hydrides have outstanding theoretical properties and have been only marginally explored, thus making this class of materials an interesting playground for both fundamental and applied research. In this review, we illustrate the most relevant results achieved in the frame of the Italian National Research Project FIRB 2010 Futuro in Ricerca “Hydrides as high capacity anodes in lithium cells” and possible future perspectives of research for this class of materials in electrochemical energy storage devices.

Pyrrolidinium-based ionic liquids with anions of the per(fluoroalkylsulfonyl)imide family are particularly interesting for their use as electrolytes in lithium batteries. These ions have several geometric isomers and the presence of different ion conformers and their distribution affects the ILs (Ionic liquids) physical and chemical properties. In the present work, we report the temperature dependence of the infrared spectra of the N-butyl-N-methyl-pyrrolidinium(trifluoromethanesulfonyl)(nonafluorobutanesulfonyl)imide (PYR14-IM14) ionic liquid; DFT (Density Functional Theory) calculations performed with different models provides indications about the IM14 conformers and their vibrational spectra. Moreover the temperature dependence of the intensity of the lines identified as markers of different conformers provide indications about the conformers' distribution and the difference of their enthalpy in the liquid phase.

Amorphous metallic membranes display promising properties for hydrogen purification up to an ultrapure grade (purity > 99.999%). The hydrogen permeability through amorphous membranes has been widely studied in the literature. In this work we focus on two additional properties, which should be considered before possible application of such materials: the propensity to crystallize at high temperatures should be avoided, as the crystallized membranes can become brittle; the hydrogen solubility should be high, as solubility and permeability are proportional. We investigate the crystallization process and the hydrogen solubility of some membranes based on Ni, Nb, and Zr metals, as a function of Zr content, and with the addition of Ta or B. The boron doping does not significantly affect the crystallization temperature and the thermal stability of the membrane. However, the hydrogen solubility for p ~7 bar is as high as H/M ~0.31 at T = 440 °C and H/M ~0.27 at T = 485 °C. Moreover, the membrane does not pulverize even after repeated thermal cycles and hydrogenation processes up to 485 °C and 7 bar, and it retains its initial shape.

We report density functional theory (DFT) calculations and low-frequency mechanical spectroscopy results on two ionic liquids having the same N -butyl- N -methyl-pyrrolidinium cation (PYR 14 ), but different anions, (nonafluorobutanesulfonyl)(toluenesulfonyl)imide (IM T4 ) and 1,3 hexafluoropropane-disulfonylimide (IM 3 ), belonging to the per(fluoroalkylsulfonyl)imide family. For both samples, a relaxation process is observed in their supercooled liquid phase, which can be described by a hopping model between non-equivalent configurations. In agreement with previous results, the relaxation is attributed to the ions motion. The comparison among calculations of the anion conformers population and the analysis of the experimental data points out that the non-equivalent configurations between which the ion motion occurs involve a different configuration for the anion.

A detailed investigation of the phase diagram of the mixtures of the two ionic liquids N-trimethyl-N-propylammonium bis(trifluoromethylsulfonyl)imide (TMPA-TFSI) and N-trimethyl-N-hexylammonium bis(trifluoromethylsulfonyl)imide (TMHA-TFSI) has been performed in the temperature range between 140 and 330 K by means of DSC and infrared spectroscopy measurements. In the low temperature crystalline states, a large concentration of trans-TFSI conformer is present in TMPA-TFSI, while almost only cis-TFSI is retained in TMHA-TFSI. For the mixtures (TMPA-TFSI)100-x (TMHA-TFSI)x, at concentrations close to the extremes, solid crystalline phases are still present and they show a strong predominance of the trans conformer of the TFSI ion for x < 15 or a large concentration of the cis conformer of TFSI for x > 85. At intermediate concentrations (33 < x < 67) no crystalline phase develops at low temperatures and both conformers of TFSI survive in the whole temperature range here investigated. We suggest that the competition between the two TFSI conformers at low temperatures can be the origin of the lack of crystalline phases for intermediate concentrations and can be exploited as a valid tool to tailor the physical properties of the mixtures of ionic liquids.

The reaction of lithium bis(trifluoromethanesulfonyl)imide with tetraphenylphosphonium bromide in water leads to the formation of tetraphenylphosphonium bis(trifluoromethanesulfonyl)imide ([PPh 4 + ][(CF 3 SO 2 ) 2 N − ]). The obtained compound was identified by means of 1 H, 13 C, 19 F and 31 P NMR spectroscopy. Although it has a structure similar to ionic liquids, it exhibits a melting point above 100 °C. Besides describing the synthesis, a detailed characterization of its conductivity and vibrational spectroscopic properties is presented. For the latter, FT-Raman and FTIR/ATR spectroscopies are used in the wavenumber range from 150 to 3500 cm −1 and from 600 to 3500 cm −1 , respectively. Density functional theory calculations reveal a minor influence of the interionic interactions on the vibrational structure. Consequently, the computational vibrational spectra of the isolated ions show a good agreement with the experimental data. A detailed vibrational assignment is presented. Furthermore, the conductivity data indicate a solid-solid phase transition about 130 K below the melting point.

MgH 2 has been recently proposed in 2008 as novel conversion material for negative electrodes in lithium ion cells (LIC). Since then, many aspects of the electrochemical behaviour in LIC of this material have been investigated: both experimental and computational studies have been carried out to investigate the fundaments of the MgH 2 conversion reaction and to demonstrate performances in LIC close to the theoretical predictions (2037 mAh g −1 and 2842 mAh cm −3 ). The conversion process involves a reversible redox reaction where the pristine binary hydride is electrochemically reduced to magnesium nanoparticles surrounded by a LiH matrix, and oxidized back to MgH 2 . In recent years the research efforts on this material have been focused on: (a) the identification of successful synthetic routes to achieve good performances in LIC; (b) the understanding of the basics of the MgH 2 conversion reaction; (c) the optimization of technological aspects to improve the performances in LIC (e.g. electrode formulation assessment and adoption of solid electrolytes). In this paper we present a comprehensive review about the research studies reported in the literature concerning the use of MgH 2 as negative electrode for lithium ion cells.

A series of mixtures prepared with different content of the ionic liquids N-trimethyl-N-propylammonium bis(trifluoromethylsulfonyl)imide (TMPA-TFSI) and N-trimethyl-N-hexylammonium bis(trifluoromethylsulfonyl)imide (TMHA-TFSI), namely, (TMPA-TFSI)100−x (TMHA-TFSI)x, is investigated by means of Raman spectroscopy as a function of pressure at room temperature. Both pure TMPA-TFSI and the x = 2 mixture crystallize under an applied pressure lower than 1 GPa. On the contrary, for x > 7, none of the investigated mixtures crystallize, but they undergo a glass transition over the 1–2 GPa pressure range. We suggest that the disorder induced by the high number of possible configurations for the longer alkyl chain of TMHA-TFSI in a compressed environment is a key factor in the suppression of the crystallization process.

The infrared spectra and their temperature dependence are measured for a series of pyrrolidinium based ionic liquids (ILs) sharing the bis(trifluoromethanesulfonyl)imide (TFSI) anion and having alkyl chains of different length. While in the liquid or glassy state, both conformers of TFSI are retained for all compounds, in the solid state a strong predominance of trans-TFSI occurs in ionic liquids with alkyl chains shorter than five C-H groups; on the contrary, for alkyl chain longer than six C-H groups crystalline phases display only cis-TFSI, which is a rare configuration in solids. Moreover, a mixed system composed of a short chain liquid (PYR14-TFSI) with one having a longer chain (PYR18-TFSI) in a mass ratio of 1:1 is studied. The competition between the two conformers of TFSI hinders the crystallization and gives rise to a glass transition around 183 K. © 2017 American Chemical Society.