Abstract Fluorinated multimetal materials have recently attracted attention as catalysts for nitrate reduction to ammonia (NO3−RR). However, their rational design and activity remain largely unexplored. Here, we report, for the first time, the NO3−RR performance of a hydrated fluorinated copper−aluminum, Cu3Al2F12(H2O)12, previously reported as a precursor of an oxyfluorinated electrocatalyst prepared by calcination. Co-precipitation synthesis, through optimization of the synthesis parameters, significantly improves its purity compared to evaporation-based synthesis. Thermal monitoring of the decomposition process of Cu3Al2F12(H2O)12 by X-ray diffraction (XRD) and thermogravimetric analysis, complemented by 19F nuclear magnetic resonance measurements, made it possible to establish the reaction scheme involving the formation of AlF3−x(OH)x and Cu(OH)F. The comparative study of the electrocatalytic properties of the fluorinated materials demonstrated that neither the synthesis method nor the calcination process significantly influenced NO3−RR performance. This led to the selection of the hydrated fluoride Cu3Al2F12(H2O)12 prepared via the simplest and scalable synthesis route, exhibiting a Faradaic efficiency of about 70% and an ammonia yield of 31 mg·h−1·mgcat−1, after 24 h in 0.1 M KNO3 at neutral pH. Postmortem characterization (electronic microscopies and XRD) reveals that the catalytically active phase generated under electrochemical conditions consists of a core−shell morphology, with smaller nanoparticles decorating the surface of the larger particles. These findings highlight the intrinsic potential of hydrated fluorinated multimetal materials as NO3−RR precatalysts.

Describing the crystal structure of disordered materials with mixed-occupancy crystallographic sites is essential for understanding their physicochemical properties and designing new materials tuned to their targeted functionalities. Here, we investigate the structure of RbM2O5F (M = Nb, Ta) pyrochlore-type oxyfluorides using a multimodal approach that combines experimental and computational techniques. Rietveld structural refinement of powder X-ray powder diffraction (PXRD) data confirmed that these oxyfluorides are isostructural, and their average crystal structure is disordered. The anionic site, 48f, is co-occupied by O and F, while the Rb site, 32e, is occupied at 25%. The shapes of the high-field solid-state 19F MAS, and 87Rb and 93Nb (CT)MAS and 3QMAS NMR spectra indicate that the local environment of these nuclei is distributed. Using the "supercell" approach, models incorporating different anion arrangements and Rb atoms distributed in their crystallographic sites were built and relaxed using density functional theory (DFT), and NMR parameters for 19F, 87Rb, and 93Nb, were computed using the PAW and GIPAW approaches. The models showing the best agreement between computed and experimental NMR parameters are made up exclusively of [MO5F]6- octahedra, [RbO15F3]32-, [RbO16F2]33-, and [RbO14F4]31- cages, indicating the existence of a preferential short-range anion ordering in these pyrochlores instead of the expected random distribution.

The structures of the ordered and isotype oxyfluorides NaMO2F2 (M = Nb, Ta) were thoroughly investigated by combining powder X-Ray Diffraction (PXRD), 19 F and high-field 23 Na and 93 Nb solid-state NMR, and DFT calculations. The structures, derived from Rietveld refinement of the PXRD data, exclusively consist of cis-[MO 4 F 2 ] 5- octahedra, in which cations are displaced from their ideal centered positions toward an oxide face. The NMR parameters were calculated for both the experimental (ES) and the atomic positions optimized (APO) structures, the latter exhibiting, as is often the case, the best agreement with the experimental data. Nb5+ and Ta5+ cations having the same size, niobium and tantalum isotypes have usually very close cell parameters. However, those of NaNbO2F2 and NaTaO2F2, particularly c , differ in unusual proportions. This difference in c parameters is due to stronger second-order Jahn-Teller effect (SOJTE) for the cis-[NbO 4 F 2 ] 5- than for the cis-[TaO 4 F 2 ] 5- octahedra, further confirmed by band structure and projected density of states calculations. Furthermore, by optimizing the synthesis conditions of these compounds using thermal analysis, a very low amplitude endothermic event, upon heating, was observed only for NaNbO2F2. An extensive analysis of the variable temperature (VT) PXRD data revealed that this event is related to a deviation from linearity of the cell parameters evolution and that structural features of these two isotypes evolve differently with temperature.

Fluorine possesses remarkable properties that ensure its enduring and indispensable role in both academic and industrial development across diverse domains of our daily lives. Nevertheless, fluorine has become a growing environmental concern, leading to the consideration of molecular fluorine (F-2) as an alternative fluorinating agent due to its low environmental impact compared to hydrofluorocarbons (HFCs) or perfluorinated compounds (PFCs). However, its pronounced toxicity, corrosiveness, and hazardous nature are problematic when handling F-2 gas cylinders. Solid storage through chemisorption via the CeF4/CeF3 transformation appears to be a promising approach to overcome its intrinsic problems. This article introduces a fundamental study exploring the impact of the chemical composition of precursor materials, CeF3 or CeO2, and the nanostructuration in the form of nanoparticles or macroporous structures on fluorination/defluorination temperatures, redox process reversibility, and the nature of the released gas, a parameter not systematically examined in previous studies. Through a deep investigation via X-ray diffraction (XRD) and electron microscopies (SEM, TEM), we demonstrate the benefit of both the pristine phase (CeO2) and the nanostructuration into a macroporous structure (OPIF) on the limitation of crystalline growth during the fluorination process. The defluorination process, monitored by TGA and gas-phase IR spectroscopy, revealed that when CeO2-OPIF undergoes fluorination to form CeF4 followed by consecutive vacuum defluorination without exposure to ambient air, incomplete decomposition of CeF4 into CeF3 results in the partial release of F-2. Conversely, exposure of the fluorinated material to air results in partial formation of a hydrate, CeF40.33H(2)O, confirmed by solid-state NMR, and promotes the defluorination (enhanced yield and release kinetics) through the formation of CeF3 with both HF and F-2 release, increasing the cyclability performance from 1 cycle to at least 8 cycles.

By selecting three different types of electrode materials, we intended to better understand the Al3+ intercalation chemistry of titanium oxide-based frameworks with an acidic chloroaluminate electrolyte. In agreement with previous reports, we confirmed that the native interstitial sites of anatase TiO2 are less prone to accommodate Al3+ than Li+ or Na+ ions, while introducing cationic vacancies largely increases the electrochemical storage capacity. Upon the first cycle, the highest reversible capacity, up to 277 mAh/g, was obtained for a hydrated layered structure featuring cationic vacancies. Total scattering data showed that the insertion of Al3+ ions induced a strong distortion of the framework. In addition, combined 27Al MAS NMR and DFT calculations revealed that in oxy-hydroxylated vacant sites, the coordination mode of Al3+ ions depends on the arrangement of anions around vacancies inducing the occurrence of 4-, 5-, and 6-fold coordination modes. Further cycling experiments revealed a progressive capacity fading for all electrode materials. Using cyclic voltammetry on the used electrolyte, we evidenced that a partial dissolution has occurred, which is more pronounced for the layered hydrate compound, and that solubilized species are electrochemically active, giving rise to specific signatures in both CVs and galvanostatic experiments. Raman spectroscopy enabled us to characterize these species, which are derived from the Ti-Cl system. The solubilized species, however, eventually precipitated, as shown by a purple deposit observed on the separator and tentatively assigned to TiCl3, known to be insoluble in this medium. By providing further information on the Al3+ intercalation chemistry and a better understanding of the electrochemical and chemical reactivities of electrode materials, this work will enable progress to be made in the development of aluminum-ion batteries.

Aqueous batteries face the challenge of limited energy density due to parasitic gas production from hydrogen and oxygen evolution reactions, particularly at the negative electrode. This study investigates the electrochemical properties and mechanisms of proton intercalation in anatase TiO2 featuring vacancies (Vac-TiO2), stabilized via a low-temperature sol-gel process. XRD refinement analysis, supported by thermal analysis, estimated 17% cationic vacancies, while H-1 MAS NMR spectroscopy revealed stabilization of these vacancies by OH groups. The presence of cationic vacancies led to changes in the oxide anion sublattice, which accommodate proton insertion. Electrochemical assessments in acetate buffer electrolyte demonstrated Vac-TiO2's ability to delay the hydrogen evolution reaction and enhance proton capacity, validated by pH-dependent studies, DFT calculations, and kinetic analyses. Notably, the occurrence of undercoordinated oxide anions was shown to induce the insertion of H+ at higher potential values, and the insertion mechanism was suggested to occur via a solid-solution mechanism. Owing to these features, Vac-TiO2 exhibited superior cyclability and performance compared to pure anatase TiO2, highlighting its potential for sustainable proton intercalation processes. In half-cell configurations, Vac-TiO2 showed a high Coulombic efficiency (CE exceeding 90% after 48 cycles), while full cells (MnO2||Vac-TiO2) demonstrated an excellent cycling stability (CE exceeding 95.4% over 1000 cycles), high power density (10.5 kWkg(-1) vs 6.2 kWkg(-1)), and improved self-discharge. This study paves the way for innovative approaches to improving proton intercalation materials, positioning Vac-TiO2 as a viable candidate for next-generation energy storage solutions.

Mechanochemistry has been widely used to enable the formation of homogenous mixed phases, particularly in the field of fluoride ion conductors. In this work, we have investigated the effect of applying long duration time of high energy ball milling on the formation of disordered fluorite BaSnF4. We have systematically compared the properties of two samples, one prepared using a commonly reported protocol and one obtained after a longer duration. Microstructural analysis obtained by X-ray line refinement and Williamson-Hall diagrams showed that increasing the ball milling time resulted in a decrease in particle size from 13 to 6 nm and suppressed the occurrence of microstrains, which were identified as twinned regions by microscopy analysis. Prolongation of the ball milling treatment is also associated with a decrease in ionic conductivity with identical fluoride ion jump activation energy. 119 Sn M & ouml;ssbauer spectroscopy revealed the presence of a new signature assigned to Sn(IV) in an oxide-fluoride environment. We hypothesized that this new environment originates from the formation of an anion-excess fluorite-type phase BaSn(II) 1-xSn(IV) x F4Oxinduced by prolonged milling. Such a hypothesis is supported by the occurrence of fluoride ions located within octahedral sites, which are likely to be bound to Sn(IV) resulting to their lower mobility as shown by 19F solid-state NMR. Overall, this work demonstrates that the interplay between the microstructure, composition and the transport properties of fluoride ion conductors is indeed complex, with many factors at play, including size, strain, defects or composition.

The tetragonal ordered form of BaSnF4 is of particular interest, as its ionic conductivity is high enough to enable its uses as an electrolyte in all-solid-state fluoride-ion batteries. Despite several studies related to its synthesis, structure, and fluoride-ion diffusion mechanism, reported routes often yield impurities as well as unexplained variation in the unit-cell c-axis length. Here, we report on the single-phase synthesis of t-BaSnF4 via spark plasma sintering, a method that could be used to prepare bulk-type all-solid-state inorganic batteries in one step. By optimizing different parameters (temperature, setup features, etc.), we reached a high ionic conductivity of 5 x 10(-3) Scm(-1) at 30 degrees C. In addition, we show that two main factors affect the ionic conductivity. First, on a microstructural scale, the preferential growth of crystallites along the c-axis results in a decrease of the ionic conductivity of resulting powders because of the two-dimensional (2D) fluoride-ion diffusion in this material. Second, on the atomic scale, the increase of the unit-cell c-axis length is concomitant with a decrease of the ionic conductivity. A combined neutron diffraction and F-19 solid-state magic angle spinning (MAS) NMR study reveals that the observed increase of the unit-cell c-axis length is due to the partial occupancy of octahedral interstitial sites. NMR allows us to identify these interstitial sites (the F4 site) with distinct isotropic chemical shift values. Furthermore, variable-temperature F-19 solid-state MAS NMR reveals that these F4-ions do not exchange with fluoride-ions (F1 and F3) that are responsible for the transport properties. Hence, the occupancy of these interstitial sites tends to lower the 2D fluoride-ion conductivity, and the unit-cell c-axis length can be used as a guideline to ensure the preparation of highly conductive samples provided that the microstructure is controlled. Overall, this study provides a novel route to prepare pure t-BaSnF4 while establishing a better understanding of the factors affecting its transport properties.

Resolving anion configurations in heteroanionic materials is crucial for understanding and controlling their properties. For anion-disordered oxyfluorides, conventional Bragg diffraction cannot fully resolve the anionic structure, necessitating alternative structure-determination methods. We have investigated the anionic structure of anion-disordered cubic (ReO3-type) TiOF2, using X-ray PDF, 19F MAS NMR analysis, density functional theory, cluster expansion modelling, and genetic algorithm structure-prediction. Our computational data predict short-range anion ordering in TiOF2, characterised by predominant cis-[O2F4] titanium coordination, resulting in correlated anion disorder at longer ranges. To validate our predictions, we generated partially disordered supercells using genetic-algorithm structure prediction and computed simulated X-ray PDF data and 19F MAS NMR spectra, which we directly compare to experimental data. To construct our simulated 19F NMR spectra, we derived new transformation functions for mapping calculated magnetic shieldings to predicted magnetic chemical shifts in titanium (oxy)fluorides, obtained by fitting DFT-calculated magnetic shieldings to previously published experimental chemical shift data for TiF4. We find good agreement between our simulated and experimental data, which supports our computationally predicted structural model, and demonstrates the effectiveness of complementary experimental and computational techniques in resolving anionic structure in anion-disordered oxyfluorides. From additional DFT calculations, we predict that increasing anion disorder makes lithium intercalation more favourable by, on average, up to 2 eV, highlighting the significant effect of variations in short-range order on the intercalation properties of anion-disordered materials.

Introducing compositional or structural disorder within crystalline solid electrolytes is a common strategy for increasing their ionic conductivity. (M,Sn)F2 fluorites have previously been proposed to exhibit two forms of disorder within their cationic host frameworks: occupational disorder from randomly distributed M and Sn cations, and orientational disorder from Sn(II) stereoactive lone pairs. Here, we characterise the structure and fluoride-ion–dynamics of cubic-BaSnF4, using a combination of experimental and computational techniques. Rietveld refinement of XRD data confirms an average fluorite structure with {Ba,Sn} cation disorder, and the 119Sn Mo ̈ssbauer spectrum demonstrates the presence of stereoactive Sn(II) lone pairs. X-ray total-scattering PDF analysis and ab initio molecular dynamics simulations reveal a complex local structure with a high degree of intrinsic fluoride-ion disorder, where 1/3 of fluoride ions occupy octahedral “interstitial” sites: this fluoride-ion disorder is a consequence of repulsion between Sn lone pairs and fluoride ions that destabilises Sn-coordinated tetrahedral fluoride-ion sites. Variable-temperature 19F NMR experiments and analysis of our molecular dynamics simulations reveal highly inhomogeneous fluoride-ion dynamics, with fluoride ions in Sn-rich local environments significantly more mobile than those in Ba-rich environments. Our simulations also reveal dynamical reorientation of the Sn lone pairs that is biased by the local cation configuration and is coupled to the local fluoride-ion dynamics. We end by discussing the effect of host-framework disorder on long-range diffusion pathways in cubic BaSnF4 .

The structure of MOF3 (M = Nb, Ta) compounds was precisely modeled by combining powder X-ray diffraction, solid-state NMR spectroscopy, and semiempirical dispersion-corrected DFT calculations. It consists of stacked ∞(MOF3) layers along the c⃗ direction formed by heteroleptic corner-connected MX6 (X = O, F) octahedra. 19F NMR resonance assignments and occupancy rates of the anionic crystallographic sites have been revised. The bridging site is shared equally by the anions, and the terminal site is occupied by F only. An O/F correlated disorder is expected since cis-MO2F4 octahedra are favored, resulting in one-dimensional -F-M-O-M- strings along the <100> and <010> directions. Ten different 2 × 2 × 1 supercells per compound, fulfilling these characteristics, were built. Using DFT calculations and the GIPAW approach, the supercells were relaxed and the 19F isotropic chemical shift values were determined. The agreement between the experimental and calculated 19F spectra is excellent for TaOF3. The 1H and 19F experimental NMR spectra revealed that some of the bridging F atoms are substituted by OH groups, especially in NbOF3. New supercells involving OH groups were generated. Remarkably, the best agreement is obtained for the supercells with the composition closest to that estimated from the 19F NMR spectra, i.e., NbOF2.85(OH)0.15.

We demonstrated that the chemical intercalation of Zn2+ions within theinterlayer space of the structure of a disordered layered titanate results in a drasticincrease of the room-temperature bulk proton conductivity from 8.11x10-5Sm-1forthepristineto 3.7x10-2Sm-1forZn-titanate. Because of the crystallographic disorderednature of these compounds, we combined different techniques to establish the structural-transport relationships. The pair distribution function revealed that upon chemicalinsertion of Zn2+, the local lepidocrocite arrangement is maintained, providing a suitablemodel to investigate the effect of chemically intercalated ions on the transport propertiesand dynamics within the interlayer space. Broadband dielectric spectroscopy (50 to 1010Hz) enabled establishing that Zn2+inclusion promotes proton-hopping by self-dissociation of H2O molecules yielding high proton mobility. Using Zn-K edgeextended X-ray absorptionfine structure and chemical analyses (EDX, TGA,1H NMR), Zn2+ions were shown to be stabilized byZnCl2(H2O) complexes within the interlayer space. Such complexes induce an increase of the H-bonding strength as evidenced by1H NMR, yielding a fast proton motion. Molecular dynamics simulations highlighted proton transfer between water molecules fromthe structural interlayer and bonded to Zn2+ions. The increasing interactions between these water molecules favor proton transfer atthe origin of the fast bulk proton conductivity, which was assigned to a Grotthuss-type mechanism taking place at a long-range order.This work provides a better understanding of how ion-water interactions mediated ionic transport and opens perspectives into thedesign of ionic conductors that can be used in energy-storage applications.

CaTiF6(H2O)2 was synthetized by a solvothermal method and was found to be isostructural to SrTiF6.2H2O. The structure, refined from Powder X-Ray Diffraction (PXRD) data, is built from the connectivity of dimers [Ca2F10(H2O)4] of square antiprisms (SAP) [CaF5(H2O)3] and TiF6 octahedra. To assign the six 19F NMR reso-nances to the six fluorine crystallographic sites of same multiplicity, 19F magnetic shielding tensors have been calculated using the GIPAW method. Unusually, the plot of the experimental 19F isotropic chemical shift (delta iso) values, as a function of the calculated 19F isotropic shielding (sigma iso) values, shows a much better alignment for the experimental structure than for the DFT-optimized one. Whereas, the dynamics of the structural water molecules under experimental conditions are not captured by the optimized structure, the experimental averaged structure provides a good account of the experimental data and a reliable assignment of the 19F resonances to the F sites. Finally, the previously established bond-valence (BV) parameter Rij for the Ti4+/F- ion pair (1.76 angstrom) leads to overestimated BV sum values for Ti. This trend has been observed for almost all other fluorotitanates. We then undertook to refine its value, using the Ti-F bond lengths from 70 carefully selected structures containing 134 Ti sites forming TiF6 octahedra, and leading to Rij = 1.706 angstrom.

In this work, the synthesis of beta-AlF3-x(OH)(x) nanoparticles with very high specific surface area (SSA) using a microwave-assisted solvothermal process is reported. The influence of synthesis parameters on the morphology and SSA was investigated, and the nature of the solvent is shown to have the greatest impact. Five samples prepared using different solvent mixtures were deeply characterized by thermogravimetric analysis (TGA), N-2 sorption, powder X-ray diffraction, transmission electron microscopy (TEM), and F-19 and Al-27 high-field solidstate NMR. Their SSAs range from 25 to 345 m(2).g(-1) with an associated OH content slightly increasing from approximate to 16% (AlF2.52(OH)(0.48)) to approximate to 19% (AlF2.42(OH)(0.58)), as estimated by TGA and Al-27 high-field solid-state NMR. Compared to previous reference work [Dambournet, D., et al. Chem. Mater. 2008, 204 1459-1469], beta-AlF3-x(OH)(x) nanoparticles with SSAs up to 4 times larger were obtained. TEM revealed the formation of hollow nanostructures except when the surface exceeds 300 m(2).g(-1), in which case isolated nanoparticles are observed. The sample with the highest SSA also displaying an appealing cumulative pore volume of 0.060 cm(3).g(-1), its hydrogen adsorption capability was evaluated to show that beta-AlF3-x(OH)(x) nanoparticles have a potential interest for hydrogen storage applications.

The successful preparation of organized porous inorganic fluorides (OPIFs) with a high specific surface area is demonstrated for MgF2. For the first time, macroporous MgF2 OPIFs with a surface area of above 200 m(2) g(-1) and mesoporous MgF2 powder were prepared through the assembly of preformed MgF2 nanoparticles and homemade polymer templates with a tunable size. These OPIF materials have been fully examined at different synthesis stages by means of powder X-ray diffraction, N-2 sorption, scanning electron microscopy, and transmission electron microscopy analyses and F-19 and H-1 solid-state nuclear magnetic resonance. The relation between the nature, the size, and the amount of polymer template on the porous structure was deeply investigated. The MgF2 OPIFs present a higher thermal stability under air and F-2 calcination than MgF2 nanoparticles as the structuration of the OPIF composite considerably slows down the crystallite growth during thermal treatment under air. OPIF materials were evaluated as heterogeneous catalysts for the fluorination of 2-chloropyridine under HF gas as a fluorinating agent at 350 degrees C. This study evidences catalytic sites with two Lewis acidity strengths (medium and low).

Topochemical reactions involving ionic exchange have been used to assess a large number of metastable compositions, particularly in layered metal oxides. This method encompasses complex reactions that are poorly explored, yet are of prime importance to understand and control the materials' properties. In this work, we embark on investigating the reactions involved during the ionic exchange between a layered Na-titanate (lepidocrocite-type structure) and an acidic solution (HCl), leading to a protonic (H3O+) titanate (trititanate structure). The reactions involve an ionic exchange provoking a structural change from the lepidocrocite-type to the trititanate structure as shown by real-space refinements of ex situ pair distribution function data. Mobile Na+ ions are exchanged by hydronium ions inducing high proton mobility in the final structure. Moreover, the reaction was followed by ex situ23Na and 1H solid-state MAS NMR which allowed, among other things, confirming that the Na+ ions are in the interlayer space and specifying their local environment. Strikingly, the ionic exchange reaction induces progressive exfoliation of the Na-titanate particles leading to 2-5 nm thin elongated crystallites. To further understand the different steps associated with the ionic exchange, the evolution of the electrolytic conductivity, using conductimetric titration, has been monitored upon HCl addition, enabling characterization of the intercalation(H+)/de-intercalation(Na+) reactions and assessing kinetic parameters. Accordingly, it is hypothesized that the exfoliation of the particles is due to the accumulation of charges at the particle level in relation to the rapid intercalation of protons. This work provides novel insights into ionic exchange reactions involved in layered oxide compounds.

Proton chemistry is a fascinating field with both fundamental and applied aspects. The development of solid-state proton conductors relying on abundant elements could help bring these two aspects. In this scope, we synthesized a disordered structure which, as revealed by the real-space refinement of the pair distribution function, has been identified to be the trititanate arrangement. The layered structure is stabilized by the presence of hydronium ions and water molecules located in the interlayer space. This compound displays a high ionic conductivity of 4.10(-2) S/m with an activation energy of 0.24 eV, assigned to H+ mobility as shown by broadband dielectric spectroscopy. Proton mobility was further evidenced by solid-state proton nuclear magnetic resonance. Density functional theory calculations revealed that proton transfer occurs both within the interlayer space and with terminal oxide of the titanate framework through a Grotthuss-based mechanism rationalizing the high conductivity measured experimentally. Finally, we investigated the electrochemical properties with respect to the proton as a charge carrier using proton-free (KCl) and proton-donor (buffer acetic acid) electrolytes. The results showed that the structure can reversibly intercalate protons at a very high rate opening existing perspectives in the development of negative electrode materials for aqueous proton batteries. Overall, this study helps better understand the proton transfer mechanism occurring in a confined layered-type structure.

High-specific-surface-area MgF2 was prepared by microwave-assisted solvothermal synthesis. The influences of the solvent and the magnesium precursors, and the calcination atmospheres, on the nanoparticle sizes and specific surface areas, estimated by X-Ray Powder Diffraction, N2 sorption and TEM analyses, were investigated. Nanocrystallized (~7 nm) magnesium partially hydroxylated fluorides (MgF2−x(OH)x) with significant specific surface areas between 290 and 330 m2∙g−1 were obtained. After activation under gaseous HF, MgF2−x(OH)x catalysts underwent a large decrease of both their surface area and their hydroxide, rates as shown by their 19F and 1H solid-state NMR spectra. Expect for MgF2 prepared from the acetate precursor, an activity of 30–32 mmol/h∙g was obtained which was about 40% higher compared with that of MgF2 prepared using Trifluoroacetate method (21.6 mmol/h∙g).

Aluminium batteries constitute a safe and sustainable high-energy-density electrochemical energy-storage solution. Viable Al-ion batteries require suitable electrode materials that can readily intercalate high-charge Al(3+)ions. Here, we investigate the Al(3+)intercalation chemistry of anatase TiO(2)and how chemical modifications influence the accommodation of Al(3+)ions. We use fluoride- and hydroxide-doping to generate high concentrations of titanium vacancies. The coexistence of these hetero-anions and titanium vacancies leads to a complex insertion mechanism, attributed to three distinct types of host sites: native interstitial sites, single vacancy sites, and paired vacancy sites. We demonstrate that Al(3+)induces a strong local distortion within the modified TiO(2)structure, which affects the insertion properties of the neighbouring host sites. Overall, specific structural features induced by the intercalation of highly polarising Al(3+)ions should be considered when designing new electrode materials for polyvalent batteries.

Crystals of two new 3D hybrid compounds, trans-Zn3TiF7(H2O)2(taz)3·3H2O and cis-Zn3TiF7(H2O)2(taz)3·C2H5OH, have been obtained by solvothermal synthesis ((taz)- = 1,2,4-triazolate C2H2N3 ligand). Their structures, determined from X-ray single crystal diffraction data in Cm and Pnma space groups, respectively, are based on Zn3N9(H2O)2F3 trimers linked by TiF6 octahedra that build trans- or cis-chains ∞[Zn3TiN9(H2O)2F7]. Water or ethanol in the structure cavities is released below 110 °C to give trans- or cis-Zn3TiF7(H2O)2(taz)3 and, on further heating, these intermediate phases dehydrate and lead to anhydrous trans- or cis-Zn3TiF7(taz)3. At 110 °C, the loss of ethanol concerns only ≈1/3 of the weight of cis-Zn3TiF7(H2O)2(taz)3·C2H5OH while the remaining part subsists up to 180 °C. This behaviour is attributed to a core-shell type configuration. Rehydration in humid air occurs at room temperature for the anhydrous cis-phase. All desolvated, dehydrated or rehydrated phase structures have been determined by X-ray powder diffraction and ab initio Rietveld refinements. All transformations from solvated or hydrated to anhydrous phases are realised without any symmetry change and the trans or cis connection of the TiF6 octahedra is maintained together with the overall features of the 3D networks. The final loss of water molecules induces a condensation reaction that implies the connection of the trimers by fluorine atoms; the structures of the anhydrous phases Zn3TiF7(taz)3 are then described by Zn3N9F4 trimers. 1H and 19F MAS NMR studies, coupled with DFT calculations of NMR parameters, confirm the water loss and support the strutural models while evidencing both the positional disorders, more likely of the organic parts, and the F motions within TiF6 octahedra.