Achieving enhanced ionic mobility in nanoporous silica by controlled surface interactions

We report a strategy to enhance the ionic mobility in an emerging class of gels, based on robust nanoporous silica micro-particles, by chemical functionalization of the silica surface. Two very different ionic liquids are used to fill the nano-pores of silica at varying pore filling factors, namely one aprotic imidazolium based (1-methyl-3-hexylimidazolium bis(trifluoromethanesulfonyl)imide, C6C1ImTFSI), and one protic ammonium based (diethylmethylammonium methanesulfonate, DEMAOMs) ionic liquid. Both these ionic liquids display higher ionic mobility when confined in functionalized silica as compared to untreated silica nano-pores, an improvement that is more pronounced at low pore filling factors (i.e. in the nano-sized pore domains) and observed in the whole temperature window investigated (i.e. from −10 to 140 °C). Solid-state NMR, diffusion NMR and dielectric spectroscopy concomitantly demonstrate this effect. The origin of this enhancement is explained in terms of weaker intermolecular interactions and a consequent flipped-ion effect at the silica interface strongly supported by 2D solid-state NMR experiments. The possibility to significantly enhance the ionic mobility by controlling the nature of surface interactions is extremely important in the field of materials science and highlights these structurally tunable gels as promising solid-like electrolytes for use in energy relevant devices. These include, but are not limited to, Li-ion batteries and proton exchange membrane (PEM) fuel cells

New Insights into the Molecular Structures, Compositions, and Cation Distributions in Synthetic and Natural Montmorillonite Clays

International audienceWe present a detailed investigation of the molecular structure of montmorillonite, an aluminosilicate clay with important applications in materials sciences, such as for catalysis, drug delivery, or as a waste barrier. Solid-state 29Si, 27Al, 25Mg, and 1H nuclear magnetic resonance (NMR) measurements combined with density functional theory (DFT) calculations provide a comprehensive picture of the local structure and composition of a synthetic clay and its naturally-occurring analogue. A revised composition is proposed based on NMR results that allow the identification and quantification of the signatures of otherwise undetectable non-crystalline impurities, thus largely complementing the traditional elemental analyses. Solid-state 1H NMR at fast magic-angle spinning (MAS) and high magnetic field provide quantitative information on intra- and inter-layer local environments that are crucial for the determination of the amount of Mg/Al substitution within the octahedral layer. In combination with DFT calculations of energies, it suggests that pairs of adjacent Mg atoms are unfavorable, leading to a non-random cationic distribution within the layers

Transport Properties, Local Coordination, and Thermal Stability of the Water/Diethylmethylammonium Methanesulfonate Binary System

Ammonium based protic ionic liquids are highlighted for their great potential to sustain proton transport in proton exchange membrane (PEM) fuel cells. Yet, there remain questions concerning the effect of water produced by the fuel cell at the cathode side on the performance of the ionic liquid. In this contribution we report the effect of water on the transport properties and the local coordination in the binary system of the protic ionic liquid diethylmethylammonium methanesulfonate ([DEMA][OMs]) and water, employing 1H NMR, Raman, and infrared spectroscopy. We observe that the self-diffusion of cations and anions increases with the water content and that cations and anions diffuse at the same rate at all concentrations investigated. 1H NMR and vibrational spectroscopy, on the other hand, indicate that added water interacts primarily with the anion and slightly affects the ionicity of the ionic liquid. In addition, by investigating the thermal stability of the binary system we find that although [DEMA][OMs] displays a continuous loss of water upon increasing temperature a fraction of water molecules can be retained even above 120 °C, and that the complete loss of water is immediately followed by decomposition, which is observed to occur at about 185 °C

Local coordination and dynamics of a protic ammonium based ionic liquid immobilized in nano-porous silica micro-particles probed by Raman and NMR spectroscopy

Room temperature ionic liquids confined in a solid material, for example, nano-porous silica, are particularly propitious for energy related applications. The aim of this study is to probe the molecular interactions established between the protic ionic liquid diethylmethylammonium methanesulfonate (DEMA-OMs) and silica, where the latter consists of nano-porous micro-particles with pores in the size range of 10 nm. The changes in the local coordination and transport properties induced by the nano-confinement of the ionic liquid are investigated by a combination of Raman and solid-state NMR spectroscopy. In particular, one-dimensional (1D) H-1 and Si-29 and two-dimensional (2D) Si-29{H-1} HETOCR solid-state NMR are combined to identify the sites of interaction at the silica-ionic liquid interface. Pulsed field gradient (PFG) NMR experiments are performed to estimate the self-diffusion of both bulk and nano-confined DEMA-OMs. Complementary information on the overall coordination and interaction scheme is achieved by Raman spectroscopy. All these advanced experimental techniques are revealed to be crucial to differentiate between ionic liquid molecules residing in the inter-or intra-particle domains

¹²⁵Te NMR Probes of Tellurium Oxide Crystals: Shielding-Structure Correlations

The local environments around tellurium atoms in a series of tellurium oxide crystals were probed by ¹²⁵Te solid-state NMR spectroscopy. Crystals with distinct TeO_<i>n</i> units (<i>n</i> from 3 to 6), including Na₂TeO₃, α-TeO₂ and γ-TeO₂, Te₂O­(PO₄)₂, K₃LaTe₂O₉, BaZnTe₂O₇, and CsYTe₃O₈ were studied. The latter four were synthesized through a solid-state process. X-ray diffraction was used to confirm the successful syntheses. The ¹²⁵Te chemical shift was found to exhibit a strong linear correlation with the Te coordination number. The ¹²⁵Te chemical-shift components (δ₁₁, δ₂₂, and δ₃₃) of the TeO₄ units were further correlated to the O–Te–O-bond angles. With the aid of ¹²⁵Te NMR, it is likely that these relations can be used to estimate the coordination states of Te atoms in unknown Te crystals and glasses

Synthesis and structure determination of CaSi1/3B2/3O8/3, a new calcium borosilicate

International audienceThis article reports on the identification, synthesis, and in-situ structure determination of a new crystalline calcium borosilicate compound of composition CaSi1/3B2/3O8/3. Synthesis was carried out by complete crystallization on annealing from a corresponding glassy composition in the widely studied CaO–SiO2–B2O3 ternary system. The crystallographic structure was determined ab initio using electron diffraction information and the charge flipping algorithm performed on synchrotron and neutron powder diffraction data collected in situ at high temperature. CaSi1/3B2/3O8/3 is found to crystallize in the Pna21 (no. 33) orthorhombic space group, with a = 12.1025(4) Å, b = 5.2676(1) Å, c = 3.7132(1) Å, and V = 236.71(1) Å3 at 650 °C. Solid-state 29Si and 11B NMR experiments have confirmed the existence of finite chains along the c axis, formed by corner-sharing SiO4 tetrahedra and BO3 units. Silicon and boron species share a crystallographic site, and the Si/B distribution induces different possible arrangements of the chains which are discussed in light of DFT calculations. At room temperature, the existence of a superstructure, resulting from the ordering within nanoscale domains, was explored by transmission electron microscopy

Synthesis and structure determination of CaSi1/3B2/3O8/3, a new calcium borosilicate

International audienceThis article reports on the identification, synthesis, and in-situ structure determination of a new crystalline calcium borosilicate compound of composition CaSi1/3B2/3O8/3. Synthesis was carried out by complete crystallization on annealing from a corresponding glassy composition in the widely studied CaO–SiO2–B2O3 ternary system. The crystallographic structure was determined ab initio using electron diffraction information and the charge flipping algorithm performed on synchrotron and neutron powder diffraction data collected in situ at high temperature. CaSi1/3B2/3O8/3 is found to crystallize in the Pna21 (no. 33) orthorhombic space group, with a = 12.1025(4) Å, b = 5.2676(1) Å, c = 3.7132(1) Å, and V = 236.71(1) Å3 at 650 °C. Solid-state 29Si and 11B NMR experiments have confirmed the existence of finite chains along the c axis, formed by corner-sharing SiO4 tetrahedra and BO3 units. Silicon and boron species share a crystallographic site, and the Si/B distribution induces different possible arrangements of the chains which are discussed in light of DFT calculations. At room temperature, the existence of a superstructure, resulting from the ordering within nanoscale domains, was explored by transmission electron microscopy

Examining the Electrochemical Properties of Hybrid Aqueous/Ionic Liquid Solid Polymer Electrolytes through the Lens of Composition-Function Relationships

Solid polymer electrolytes (SPEs) have the potential to meet evolving Li-ion battery demands, but for these electrolytes to satisfy growing power and energy density requirements, both transport properties and electrochemical stability must be improved. Unfortunately, improvement in one of these properties often comes at the expense of the other. To this end, a “hybrid aqueous/ionic liquid” SPE (HAILSPE) which incorporates triethylsulfonium-TFSI (S2,2,2) or N-methyl-N-propylpyrrolidinium-TFSI (Pyr1,3) ionic liquid (IL) alongside H2O and LiTFSI salt to simultaneously improve transport and electrochemical stability is studied. This work focuses on the impact of HAILSPE composition on electrochemical performance. Analysis shows that an increase in LiTFSI content results in decreased ionic mobility, while increasing IL and water content can offset its impact. pfg-NMR results reveal that preferential lithium-ion transport is present in HAILSPE systems. Higher IL concentrations are correlated with an increased degree of passivation against H2O reduction. Compared to the Pyr1,3 systems, the S2,2,2 systems exhibit a stronger degree of passivation due to the formation of a multicomponent interphase layer, including LiF, Li2CO3, Li2S, and Li3N. The results herein demonstrate the superior electrochemical stability of the S2,2,2 systems compared to Pyr1,3 and provide a path toward further enhancement of HAILSPE performance via composition optimization.https://doi.org/10.1002/aenm.20230142

Noticiero de Vigo : diario independiente de la mañana: Ano XXVII Número 11366 - 1912 outubro 26

This article reports on the identification, synthesis, and in-situ structure determination of a new crystalline calcium borosilicate compound of composition CaSi_1/3B_2/3O_8/3. Synthesis was carried out by complete crystallization on annealing from a corresponding glassy composition in the widely studied CaO–SiO₂–B₂O₃ ternary system. The crystallographic structure was determined ab initio using electron diffraction information and the charge flipping algorithm performed on synchrotron and neutron powder diffraction data collected in situ at high temperature. CaSi_1/3B_2/3O_8/3 is found to crystallize in the <i>Pna</i>2₁ (no. 33) orthorhombic space group, with <i>a</i> = 12.1025(4) Å, <i>b</i> = 5.2676(1) Å, <i>c</i> = 3.7132(1) Å, and <i>V</i> = 236.71(1) ų at 650 °C. Solid-state ²⁹Si and ¹¹B NMR experiments have confirmed the existence of finite chains along the <i>c</i> axis, formed by corner-sharing SiO₄ tetrahedra and BO₃ units. Silicon and boron species share a crystallographic site, and the Si/B distribution induces different possible arrangements of the chains which are discussed in light of DFT calculations. At room temperature, the existence of a superstructure, resulting from the ordering within nanoscale domains, was explored by transmission electron microscopy

New Insights into the Molecular Structures, Compositions, and Cation Distributions in Synthetic and Natural Montmorillonite Clays

We present a detailed investigation of the molecular structure of montmorillonite, an aluminosilicate clay with important applications in materials sciences, such as for catalysis, drug delivery, or as a waste barrier. Solid-state ²⁹Si, ²⁷Al, ²⁵Mg, and ¹H nuclear magnetic resonance (NMR) measurements combined with density functional theory (DFT) calculations provide a comprehensive picture of the local structure and composition of a synthetic clay and its naturally occurring analogue. A revised composition is proposed based on NMR results that allow the identification and quantification of the signatures of otherwise undetectable noncrystalline impurities, thus largely complementing the traditional elemental analyses. Solid-state ¹H NMR at fast magic-angle spinning (MAS) and high magnetic field provide quantitative information on intra- and interlayer local environments that are crucial for the determination of the amount of Mg/Al substitution within the octahedral layer. In combination with DFT calculations of energies, it suggests that pairs of adjacent Mg atoms are unfavorable, leading to a nonrandom cationic distribution within the layers