Ionic conduction in ammonia functionalised closo-dodecaborates MB12H11NH3 (M = Li and Na)

Metal hydroborates and their derivatives have been receiving attention as potential solid-state ion conductors for battery applications owing to their impressive electrochemical and mechanical characteristics. However, to date only a fraction of these compounds has been investigated as solid-state electrolytes. Here, MB12H11NH3 (M = Li and Na) hydroborates are synthesized and investigated as electrolyte materials for all-solid-state batteries. The room temperature α-NaB12H11NH3 was structurally solved in P212121 (a = 7.1972(3) Å, b = 9.9225(4) Å, and c = 14.5556(5) Å). It shows a polymorphic structural transition near 140 °C to cubic Fm3̄m. LiB12H11NH3 and NaB12H11NH3 exhibit cationic conductivities of σ(Li+) = 3.0 × 10-4 S cm-1 and σ(Na+) = 1.2 × 10-4 S cm-1 at 200 °C. Hydration is found to improve ionic conductivity of the hydroborates. It is presumed that modest ionic conductivities could be due to a lack of significant re-orientational dynamics in the crystal structure resulting from the presence of the bulky -NH3 group in the anion.

Establishing ZIF-8 as a reference material for hydrogen cryoadsorption: An interlaboratory study

Hydrogen storage by cryoadsorption on porous materials has the advantages of low material cost, safety, fast kinetics, and high cyclic stability. The further development of this technology requires reliable data on the H2 uptake of the adsorbents, however, even for activated carbons the values between different laboratories show sometimes large discrepancies. So far no reference material for hydrogen cryoadsorption is available. The metal-organic framework ZIF-8 is an ideal material possessing high thermal, chemical, and mechanical stability that reduces degradation during handling and activation. Here, we distributed ZIF-8 pellets synthesized by extrusion to 9 laboratories equipped with 15 different experimental setups including gravimetric and volumetric analyzers. The gravimetric H2 uptake of the pellets was measured at 77 K and up to 100 bar showing a high reproducibility between the different laboratories, with a small relative standard deviation of 3-4 % between pressures of 10-100 bar. The effect of operating variables like the amount of sample or analysis temperature was evaluated, remarking the calibration of devices and other correction procedures as the most significant deviation sources. Overall, the reproducible hydrogen cryoadsorption measurements indicate the robustness of the ZIF-8 pellets, which we want to propose as a reference material.

Alkali metal alkoxyborate ester salts; a contemporary look at old compounds

Research into the use of sodium tetraalkoxyborate salts for different chemical applications including synthetic catalysis, hydrogen storage, or battery applications has been investigated, however, understanding of the structural, thermal and electrochemical properties of these salts has been lacking since the 1950s and 1960s. A review of the synthesis, as well as a thorough characterization using 1H NMR, 11B NMR, 13C{1H} NMR, FTIR, XRD, in situ XRD, DSC-TGA, RGA-MS, TPPA, and EIS has newly identified polymorphic phase changes for Na[B(OMe)4], K[B(OMe)4], Li[B(OMe)4], Na[B(OEt)4], Na[B(OBu)4], and Na[B(OiBu)4]. The crystal structure of K[B(OMe)4] was also solved in I41/a (a = 22.337(2) Å, c = 7.648(3) Å, V = 3815.6(4) Å3, ρ = 1.128(1) g cm-3). Ionic conductivity of the different salts was analyzed, however it was found that the compounds with longer alkyl chains had no measurable ionic conductivity compared to the shorter chained samples, Na[B(OMe)4] and K[B(OMe)4] with 9.6 × 10-8 S cm-1 and 1.6 × 10-7 S cm-1, at 114 °C respectively.

Producing Alkali Metal Hydrides from Hydroxides

In this study, a novel method for producing different alkali metal hydrides (NaH, KH, RbH, and CsH) from their corresponding metal hydroxides (NaOH, KOH, RbOH, and CsOH) is presented. For the production of NaH from NaOH, a variety of metallic reducing agents (Mg, Al, Si, CaH2, Cr, Mn, and Sr) were investigated. The reactions took place in an autoclave reactor with paraffin oil at 250 °C and 14 bar of H2 pressure. Splitting the process into two steps (metal formation and hydrogenation) simplified the separation and purification for the produced metal hydride. Moreover, the study explores the potential for this method of NaH production to be used for NaBH4 production and regeneration for hydrogen export applications. This approach offers an alternative, cost-effective method for producing NaH.

Stannaborates: tuning the ion conductivity of dodecaborate salts with tin substitution

Metal substituted dodecaborate anions can be coupled with alkali metal cations to have great potential as solid-state ion conductors for battery applications. A tin atom can replace a B-H unit within an unsubstituted dodecaborate cage to produce a stable, polar divalent anion. The chemical and structural change in forming a stannaborate results in a modified crystal structure of respective group 1 metal salts, and as a result, improves the material's ion conductivity. Li2B11H11Sn shows high ion conductivity of ∼8 mS cm-1 at 130 °C, similar to the state-of-the-art LiCB11H12 at these temperatures, however, obtaining high ion conductivity at room temperature is not possible with pristine alkali metal stannaborates.

Role of π-Radical Localization on Thermally Stable Cross-Links Between Polycyclic Aromatic Hydrocarbons

The thermal stability of cross-links between polycyclic aromatic hydrocarbons (PAHs) is critical for understanding the formation of soot pollutants, graphite, and carbon blacks. Recently, a variety of different π-radicals have been directly imaged and suggested to enable thermally stable bonding; however, a systematic study of reactivity has been lacking. In this work, we use density functional theory to study the reactivity of PAH π-radicals. The Mulliken spin densities are initially used to categorize the different classes of localization, and the bond energy is computed to determine the degree of localization required for thermal stability. The results showed that the bond energies of PAHs are strongly correlated with the calculated spin densities, but bond energies do not exist with the bond lengths due to significant rearrangement and steric effects during bond formation. A threshold for π-radical localization is suggested that will be stable in combustion and pyrolysis environments of ρMα ≥ 0.5. Finally, the formation of multicenter bonds between localized and delocalized π-radicals was investigated using the nudge elastic band (NEB) scan, and it was found that only delocalized π-radicals provided local energy minima. These results show that the localization of π-radicals is critical for the formation of thermally stable single-center bonds between aromatic radicals.

Thermochemical energy storage in barium carbonate enhanced by iron(III) oxide

Renewable energy requires cost effective and reliable storage to compete with fossil fuels. This study introduces a new reactive carbonate composite (RCC) where Fe₂O₃ is used to thermodynamically destabilise BaCO₃ and reduce its decomposition temperature from 1400 °C to 850 °C, which is more suitable for thermal energy storage applications. Fe₂O₃ is consumed on heating to form BaFe₁₂O₁₉, which is a stable Fe source for promoting reversible CO₂ reactions. Two reversible reaction steps were observed that corresponded to, first, the reaction between β-BaCO₃ and BaFe₁₂O₁₉, and second, between γ-BaCO₃ and BaFe₁₂O₁₉. The thermodynamic parameters were determined to be ΔH = 199 ± 6 kJ mol^-1 of CO₂, ΔS = 180 ± 6 J K^-1 mol^-1 of CO₂ and ΔH = 212 ± 6 kJ mol^-1 of CO₂, ΔS = 185 ± 7 J K^-1 mol^-1 of CO₂, respectively, for the two reactions. Due to the low-cost and high gravimetric and volumetric energy density, the RCC is demonstrated to be a promising candidate for next generation thermal energy storage.

Divalent closo-monocarborane solvates for solid-state ionic conductors

Li-ion batteries have held the dominant position in battery research for the last 30+ years. However, due to inadequate resources and the cost of necessary elements (e.g., lithium ore) in addition to safety issues concerning the components and construction, it has become more important to look at alternative technologies. Multivalent metal batteries with solid-state electrolytes are a potential option for future battery applications. The synthesis and characterisation of divalent hydrated closo-monocarborane salts - Mg[CB₁₁H₁₂]₂·xH₂O, Ca[CB₁₁H₁₂]₂·xH₂O, and Zn[CB₁₁H₁₂]₂·xH₂O - have shown potential as solid-state electrolytes. The coordination of a solvent (e.g. H₂O) to the cation in these complexes shows a significant improvement in ionic conductivity, i.e. for Zn[CB₁₁H₁₂]₂·xH₂O dried at 100 °C (10^-3 S cm^-1 at 170 °C) and dried at 150 °C (10^-5 S cm^-1 at 170 °C). Solvent choice also proved important with the ionic conductivity of Mg[CB₁₁H₁₂]₂·3en (en = ethylenediamine) being higher than that of Mg[CB₁₁H₁₂]₂·3.1H₂O (2.6 × 10^-5 S cm^-1 and 1.7 × 10^-8 S cm^-1 at 100 °C, respectively), however, the oxidative stability was lower (<1 V (Mg²⁺/Mg) and 1.9 V (Mg²⁺/Mg), respectively). Thermal characterisation of the divalent closo-monocarborane salts showed melting and desolvation, prior to high temperature decomposition.

Na2B11H13 and Na11(B11H14)3(B11H13)4 as potential solid-state electrolytes for Na-ion batteries

Solid-state sodium batteries have attracted great attention owing to their improved safety, high energy density, large abundance and low cost of sodium compared to the current Li-ion batteries. Sodium-boranes have been studied as potential solid-state electrolytes and the search for new materials is necessary for future battery applications. Here, a facile and cost-effective solution-based synthesis of Na₂B₁₁H₁₃ and Na₁₁(B₁₁H₁₄)₃(B₁₁H₁₃)₄ is demonstrated. Na₂B₁₁H₁₃ presents an ionic conductivity in the order of 10^-7 S cm^-1 at 30 °C, but undergoes an order-disorder phase transition and reaches 10^-3 S cm^-1 at 100 °C, close to that of liquids and the solid-state electrolyte Na-β-Al₂O₃. The formation of a mixed-anion solid-solution, Na₁₁(B₁₁H₁₄)₃(B₁₁H₁₃)₄, partially stabilises the high temperature structural polymorph observed for Na₂B₁₁H₁₃ at room temperature and it exhibits Na⁺ conductivity higher than its constituents (4.7 × 10^-5 S cm^-1 at 30 °C). Na₂B₁₁H₁₃ and Na₁₁(B₁₁H₁₄)₃(B₁₁H₁₃)₄ exhibit an oxidative stability limit of 2.1 V vs. Na⁺/Na.

Synthesis of closo-CB11H12- Salts Using Common Laboratory Reagents

Lithium and sodium salts of the closo-carbadodecaborate anion [CB₁₁H₁₂]^- have been shown to form stable solid-state electrolytes with excellent ionic conductivity for all-solid-state batteries (ASSB). However, potential commercial application is currently hindered by the difficult, low-yielding, and expensive synthetic pathways. We report a novel and cost-effective method to synthesize the [CB₁₁H₁₂]^- anion in a 40% yield from [B₁₁H₁₄]^-, which can be synthesized using common laboratory reagents. The method avoids the use of expensive and dangerous reagents such as NaH, decaborane, and CF₃SiMe₃ and shows excellent reproducibility in product yield and purity.

Polymorphism of Calcium Decahydrido-closo-decaborate and Characterization of Its Hydrates

Metal closo-borates and their derivatives have shown promise in several fields of application from cancer therapy to solid-state electrolytes partly owing to their stability in aqueous solutions and high thermal stability. We report the synthesis and structural analysis of α- and β-CaB₁₀H₁₀, which are structurally and energetically similar, both showing a tetrahedral coordination of Ca²⁺ to four closo-borate cages. The main distinctions between the α- and β-polymorph are found in the crystal system (monoclinic or orthorhombic), topology (wurtzite or cag), and the degree of displacement of Ca²⁺ from the center of the coordination tetrahedron. Neutron vibrational spectroscopy measurements further revealed distinct perturbations in the cation-anion interactions arising from the different crystal structures. We also synthesized and structurally investigated five stoichiometric hydrates, CaB₁₀H₁₀·xH₂O, x = 1, 4, 5, 6, and 7, and discovered an order-disorder polymorphic transition, α- to β-CaB₁₀H₁₀·6H₂O. The hydrates reveal a rich structural diversity with ordered structures, CaB₁₀H₁₀·xH₂O, x = 1, 4, 5, 6, and 7, as well as disordered structures, x = 6 and 8. The latter allow for a continuum of compositions within 7-8 molecules of crystal water. The DFT-optimized experimental crystal structures reveal complex networks of three types of hydrogen interactions: dihydrogen bonds, B-H^δ-···^+δH-O; hydrogen-hydrogen interactions, B-H···H-B; and hydrogen bonds, O-H^δ+···^-δO-H. A rather short B-H···H-B (2.14 Å) interaction is observed for CaB₁₀H₁₀·5H₂O, which is locally stabilized by four hydrogen bonds.

Thermal properties of thermochemical heat storage materials

The thermal conductivity, thermal diffusivity and heat capacity of materials are all vital properties in the determination of the efficiency of a thermal system. However, the thermal transport properties of heat storage materials are not consistent across previous studies, and are strongly dependent on the sample composition and measurement method. A comprehensive analysis of thermal transport properties using a consistent preparation and measurement method is lacking. This study aims to provide the foundation for a detailed insight into thermochemical heat storage material properties with consistent measurement methods. The thermal transport properties of pelletised metal hydrides, carbonates and oxides were measured using the transient plane source method to provide the thermal conductivity, thermal diffusivity and heat capacity. This information is valuable in the development of energy storage and chemical processing systems that are highly dependent on the thermal conductivity of materials.

Thermochemical energy storage performance of zinc destabilized calcium hydride at high-temperatures

CaH2 has 20 times the energy density of molten salts and was patented in 2010 as a potential solar thermal energy storage material. Unfortunately, its high operating temperature (>1000 °C) and corrosivity at that temperature make it challenging to use as a thermal energy storage (TES) material in concentrating solar power (CSP) plants. To overcome these practical limitations, here we propose the thermodynamic destabilization of CaH2 with Zn metal. It is a unique approach that reduces the decomposition temperature of pure CaH2 (1100 °C at 1 bar of H2 pressure) to 597 °C at 1 bar of H2 pressure. Its new decomposition temperature is closer to the required target temperature range for TES materials used in proposed third-generation high-temperature CSP plants. A three-step dehydrogenation reaction between CaH2 and Zn (1 : 3 molar ratio) was identified from mass spectrometry, temperature-programmed desorption and in situ X-ray diffraction studies. Three reaction products, CaZn13, CaZn11 and CaZn5, were confirmed from in situ X-ray diffraction studies at 190 °C, 390 °C and 590 °C, respectively. The experimental enthalpy and entropy of the second hydrogen release reaction were determined by pressure composition isotherm measurements, conducted between 565 and 614 °C, as ΔHdes = 131 ± 4 kJ mol-1 H2 and ΔSdes = 151 ± 4 J K-1 mol-1 H2. Hydrogen cycling studies of CaZn11 at 580 °C showed sufficient cycling capacity with no significant sintering occurring during heating, as confirmed by scanning electron microscopy, demonstrating its great potential as a TES material for CSP applications. Finally, a cost comparison study of known destabilized CaH2 systems was carried out to assess the commercial potential.

Decomposition pathway of KAlH4 altered by the addition of Al2S3

Altering the decomposition pathway of potassium alanate, KAlH4, with aluminium sulfide, Al2S3, presents a new opportunity to release all of the hydrogen, increase the volumetric hydrogen capacity and avoid complications associated with the formation of KH and molten K. Decomposition of 6KAlH4-Al2S3 during heating under dynamic vacuum began at 185 °C, 65 °C lower than for pure KAlH4, and released 71% of the theoretical hydrogen content below 300 °C via several unknown compounds. The major hydrogen release event, centred at 276 °C, was associated with two new compounds indexed with monoclinic (a = 10.505, b = 7.492, c = 11.772 Å, β = 122.88°) and hexagonal (a = 10.079, c = 7.429 Å) unit cells, respectively. Unlike the 6NaAlH4-Al2S3 system, the 6KAlH4-Al2S3 system did not have M3AlH6 (M = alkali metal) as one of the intermediate decomposition products nor were the final products M2S and Al observed. Decomposition performed under hydrogen pressure initially followed a similar reaction pathway to that observed during heating under vacuum but resulted in partial melting of the sample between 300 and 350 °C. The measured enthalpy of hydrogen absorption (ΔHabs) was in the range -44.5 to -51.1 kJ mol-1 H2, which is favourable for moderate temperature hydrogen applications. Although, the hydrogen capacity decreases during consecutive H2 release and uptake cycles, the presence of excess amounts of aluminium allow for further optimisation of hydrogen storage properties.

Molten metal closo-borate solvates

Li₂B₁₂H₁₂ is reported in the molten state for the first time, which enables a range of new research opportunities.

From Metal Hydrides to Metal Borohydrides

Commencing from metal hydrides, versatile synthesis, purification, and desolvation approaches are presented for a wide range of metal borohydrides and their solvates. An optimized and generalized synthesis method is provided for 11 different metal borohydrides, M(BH₄) _n, (M = Li, Na, Mg, Ca, Sr, Ba, Y, Nd, Sm, Gd, Yb), providing controlled access to more than 15 different polymorphs and in excess of 20 metal borohydride solvate complexes. Commercially unavailable metal hydrides (MH _n, M = Sr, Ba, Y, Nd, Sm, Gd, Yb) are synthesized utilizing high pressure hydrogenation. For synthesis of metal borohydrides, all hydrides are mechanochemically activated prior to reaction with dimethylsulfide borane. A purification process is devised, alongside a complementary desolvation process for solvate complexes, yielding high purity products. An array of polymorphically pure metal borohydrides are synthesized in this manner, supporting the general applicability of this method. Additionally, new metal borohydrides, α-, α'- β-, γ-Yb(BH₄)₂, α-Nd(BH₄)₃ and new solvates Sr(BH₄)₂·1THF, Sm(BH₄)₂·1THF, Yb(BH₄)₂· xTHF, x = 1 or 2, Nd(BH₄)₃·1Me₂S, Nd(BH₄)₃·1.5THF, Sm(BH₄)₃·1.5THF and Yb(BH₄)₃· xMe₂S (" x" = unspecified), are presented here. Synthesis conditions are optimized individually for each metal, providing insight into reactivity and mechanistic concerns. The reaction follows a nucleophilic addition/hydride-transfer mechanism. Therefore, the reaction is most efficient for ionic and polar-covalent metal hydrides. The presented synthetic approaches are widely applicable, as demonstrated by permitting facile access to a large number of materials and by performing a scale-up synthesis of LiBH₄.

Thermodynamics and performance of the Mg-H-F system for thermochemical energy storage applications

Magnesium hydride (MgH₂) is a hydrogen storage material that operates at temperatures above 300 °C. Unfortunately, magnesium sintering occurs above 420 °C, inhibiting its application as a thermal energy storage material. In this study, the substitution of fluorine for hydrogen in MgH₂ to form a range of Mg(H_xF_1-x)₂ (x = 1, 0.95, 0.85, 0.70, 0.50, 0) composites has been utilised to thermodynamically stabilise the material, so it can be used as a thermochemical energy storage material that can replace molten salts in concentrating solar thermal plants. These materials have been studied by in situ synchrotron X-ray diffraction, differential scanning calorimetry, thermogravimetric analysis, temperature-programmed-desorption mass spectrometry and Pressure-Composition-Isothermal (PCI) analysis. Thermal analysis has determined that the thermal stability of Mg-H-F solid solutions increases proportionally with fluorine content, with Mg(H_0.85F_0.15)₂ having a maximum rate of H₂ desorption at 434 °C, with a practical hydrogen capacity of 4.6 ± 0.2 wt% H₂ (theoretical 5.4 wt% H₂). An extremely stable Mg(H_0.43F_0.57)₂ phase is formed upon the decomposition of each Mg-H-F composition of which the remaining H₂ is not released until above 505 °C. PCI measurements of Mg(H_0.85F_0.15)₂ have determined the enthalpy (ΔH_des) to be 73.6 ± 0.2 kJ mol^-1 H₂ and entropy (ΔS_des) to be 131.2 ± 0.2 J K^-1 mol^-1 H₂, which is slightly lower than MgH₂ with ΔH_des of 74.06 kJ mol^-1 H₂ and ΔS_des = 133.4 J K^-1 mol^-1 H₂. Cycling studies of Mg(H_0.85F_0.15)₂ over six absorption/desorption cycles between 425 and 480 °C show an increased usable cycling temperature of ∼80 °C compared to bulk MgH₂, increasing the thermal operating temperatures for technological applications.

Structure and Hydrogenation Properties of a HfNbTiVZr High-Entropy Alloy

A high-entropy alloy (HEA) of HfNbTiVZr was synthesized using an arc furnace followed by ball milling. The hydrogen absorption mechanism was studied by in situ X-ray diffraction at different temperatures and by in situ and ex situ neutron diffraction experiments. The body centered cubic (BCC) metal phase undergoes a phase transformation to a body centered tetragonal (BCT) hydride phase with hydrogen occupying both tetrahedral and octahedral interstitial sites in the structure. Hydrogen cycling of the alloy at 500 °C is stable. The large lattice strain in the HEA seems favorable for absorption in both octahedral and tetrahedral sites. HEAs therefore have potential as hydrogen storage materials because of favorable absorption in all interstitial sites within the structure.

Hydrogenation properties of lithium and sodium hydride – closo-borate, [B10H10]2− and [B12H12]2−, composites

The hydrogen absorption properties of metal closo-borate/metal hydride composites are studied under high hydrogen pressures.

Metal borohydrides and derivatives – synthesis, structure and properties

A comprehensive review of metal borohydrides from synthesis to application.

Metal borohydride formation from aluminium boride and metal hydrides

Formation and quantification of metal borohydrides at high pressure, p(H₂) = 600 bar, and elevated temperature from AlB₂-MH_x (M = Li, Na, Mg, Ca) composites.

Sulfurized metal borohydrides

The reactions between metal borohydrides and elemental sulfur are investigatedin situduring thermal treatment and are found to be highly exothermic (up to 700 J g⁻¹).

Stabilization of volatile Ti(BH4)3 by nano-confinement in a metal-organic framework

Volatile Ti(BH₄)₃ molecules stabilized on the surface of a MOF.

Liquid complex hydrides are a new class of hydrogen storage materials with several advantages over solid hydrides, e.g. they are flexible in shape, they are a flowing fluid and their convective properties facilitate heat transport. The physical and chemical properties of a gaseous hydride change when the molecules are adsorbed on a material with a large specific surface area, due to the interaction of the adsorbate with the surface of the host material and the reduced number of collisions between the hydride molecules. In this paper we report the synthesis and stabilization of gaseous Ti(BH₄)₃. The compound was successfully stabilized through adsorption in nanocavities. Ti(BH₄)₃, upon synthesis in its pure form, spontaneously and rapidly decomposes into diborane and titanium hydride at room temperature in an inert gas, e.g. argon. Ti(BH₄)₃ adsorbed in the cavities of a metal organic framework is stable for several months at ambient temperature and remains stable up to 350 K under vacuum. The adsorbed Ti(BH₄)₃ reaches approximately twice the density of the gas phase. The specific surface area (BET, N₂ adsorption) of the MOF decreased from 1200 m² g^–1 to 770 m² g^–1 upon Ti(BH₄)₃ adsorption.

Hydrogen Storage Materials for Mobile and Stationary Applications: Current State of the Art

One of the limitations to the widespread use of hydrogen as an energy carrier is its storage in a safe and compact form. Herein, recent developments in effective high-capacity hydrogen storage materials are reviewed, with a special emphasis on light compounds, including those based on organic porous structures, boron, nitrogen, and aluminum. These elements and their related compounds hold the promise of high, reversible, and practical hydrogen storage capacity for mobile applications, including vehicles and portable power equipment, but also for the large scale and distributed storage of energy for stationary applications. Current understanding of the fundamental principles that govern the interaction of hydrogen with these light compounds is summarized, as well as basic strategies to meet practical targets of hydrogen uptake and release. The limitation of these strategies and current understanding is also discussed and new directions proposed.

In situX-ray diffraction environments for high-pressure reactions

New sample environments and techniques specifically designed forin situpowder X-ray diffraction studies up to 1000 bar (1 bar = 105 Pa) gas pressure are reported and discussed. The cells can be utilized for multiple purposes in a range of research fields. Specifically, investigations of gas–solid reactions and sample handling under inert conditions are undertaken here. Sample containers allowing the introduction of gas from one or both ends are considered, enabling the possibility of flow-through studies. Various containment materials are evaluated,e.g.capillaries of single-crystal sapphire (Al2O3), quartz glass (SiO2), stainless steel (S316) and glassy carbon (Sigradur K), and burst pressures are calculated and tested for the different tube materials. In these studies, high hydrogen pressure is generated with a metal hydride hydrogen compressor mounted in a closed system, which allows reuse of the hydrogen gas. The advantages and design considerations of thein situcells are discussed and their usage is illustrated by a case study.

Novel solvates M(BH₄)₃S(CH₃)₂ and properties of halide-free M(BH₄)₃ (M = Y or Gd)

Rare earth metal borohydrides have been proposed as materials for solid-state hydrogen storage because of their reasonably low temperature of decomposition. New synthesis methods, which provide halide-free yttrium and gadolinium borohydride, are presented using dimethyl sulfide and new solvates as intermediates. The solvates M(BH4)3S(CH3)2 (M = Y or Gd) are transformed to α-Y(BH4)3 or Gd(BH4)3 at ~140 °C as verified by thermal analysis. The monoclinic structure of Y(BH4)3S(CH3)2, space group P2₁/c, a = 5.52621(8), b = 22.3255(3), c = 8.0626(1) Å and β = 100.408(1)°, is solved from synchrotron radiation powder X-ray diffraction data and consists of buckled layers of slightly distorted octahedrons of yttrium atoms coordinated to five borohydride groups and one dimethyl sulfide group. Significant hydrogen loss is observed from Y(BH4)3 below 300 °C and rehydrogenation at 300 °C and p(H2) = 1550 bar does not result in the reformation of Y(BH4)3, but instead yields YH3. Moreover, composites systems Y(BH4)3-LiBH4 1 : 1 and Y(BH4)3-LiCl 1 : 1 prepared from as-synthesised Y(BH4)3 are shown to melt at 190 and 220 °C, respectively.

Structural and kinetic investigation of the hydride composite Ca(BH4)2 + MgH2 system doped with NbF5 for solid-state hydrogen storage

NbF₅ reduces dehydrogenation temperature of Ca(BH₄)₂ + MgH₂ system by 100 °C. Here, we give a possible elucidation of this effect.

Hydriding characteristics of NaMgH2F with preliminary technical and cost evaluation of magnesium-based metal hydride materials for concentrating solar power thermal storage

An economic assessment is performed on NaMgH₂F and magnesium-based metal hydrides as heat storage materials for concentrating solar thermal power.

Mechanochemical synthesis of amorphous silicon nanoparticles

Solid–liquid mechanochemical ball-milling to produce tuneable Si nanoparticle sizes to improve hydrogen storage system reaction kinetics.

Encapsulation and sustained release of curcumin using superparamagnetic silica reservoirs

For controlled release and targeted delivery of curcumin in an aqueous medium a method of encapsulating curcumin and magnetic nanoparticles inside porous silica matrix has been developed. Curcumin and superparamagnetic nanoparticles are loaded inside porous silica in a single process. The graphic shows the TEM image of microtomed sample of Fe(3)O(4) particles surrounded by a silica matrix.

Preparation, microstructure and hydrogen sorption properties of nanoporous carbon aerogels under ambient drying

Organic aerogels are prepared by the sol-gel method from polymerization of resorcinol with furfural. These aerogels are further carbonized in nitrogen in order to obtain their corresponding carbon aerogels (CA); a sample which was carbonized at 900 °C was also activated in a carbon dioxide atmosphere at 900 °C. The chemical reaction mechanism and optimum synthesis conditions are investigated by means of Fourier transform infrared spectroscopy and thermoanalyses (thermogravimetric/differential thermal analyses) with a focus on the sol-gel process. The carbon aerogels were investigated with respect to their microstructures, using small angle x-ray scattering (SAXS), transmission electron microscopy (TEM) and nitrogen adsorption measurements at 77 K. SAXS studies showed that micropores with a radius of gyration of <0.35 ± 0.07 to 0.55 ± 0.05 nm were present, and TEM measurements and nitrogen adsorption showed that larger mesopores were also present. Hydrogen storage properties of the CA were also investigated. An activated sample with a Brunauer-Emmett-Teller surface area of 1539 ± 20 m(2) g(-1) displayed a reasonably high hydrogen uptake at 77 K with a maximum hydrogen sorption of 3.6 wt% at 2.5 MPa. These results suggest that CA are promising candidate hydrogen storage materials.

Wormlike micelles from a cage amine metallosurfactant

We have shown that copper and cobalt metallosurfactants derived from Cu(II) and Co(III) complexes of a macrobicyclic hexamine ("cage") can form wormlike micelles in aqueous solution that may coexist with or easily interconvert with vesicle structures. The cylindrical micelle structures are unusual for triple-chain surfactants with a single headgroup and are not easily accounted for using geometrical packing arguments. The solution behavior has been characterized by cryo-TEM and SAXS measurements. Both the Cu and Co compounds display viscoelastic solutions at 1 wt %, indicating that such behavior may be anticipated for the full variety of stable metal complexes formed by the cage headgroup, auguring applications based on the incorporation of metallo aggregates into mesoporous silica structures.

Analysis of polydisperse bubbles in the aluminium–hydrogen system using a size-dependent contrast

The characterization of hydrogen defects in an aluminium–hydrogen system was performed previously [Buckleyet al.(2001).J. Appl. Cryst.34, 119–129] using small-angle scattering, inelastic neutron scattering and electron microscopy techniques. This analysis resulted in the determination of the relative change in lattice parameter as a result of hydrogen introduction into the Al matrix. However, this method relied on the average volume of the bubbles of hydrogen and also the pressure in a bubble of average volume. The characterization of the Al–H system has been improved by considering the size polydispersity of the hydrogen bubbles. The determination of a volume-fraction size distribution of the bubbles from small-angle scattering data has allowed a polydispersity analysis to be undertaken. A size-dependent contrast has been utilized in the modification of the volume-fraction size distribution into a more accurate form that accounts for varying concentrations of hydrogen within bubbles of different sizes. The determination of the size-dependent contrast is based upon an equation of state for molecular hydrogen which incorporates the compressibility of hydrogen under high pressures. The formation of alane (AlH3) is also investigated, as it can be formed by the chemisorption of hydrogen in aluminium under high pressures. The polydispersity analysis has allowed a more accurate description of the Al–H system and can be applied to similar scattering systems where the scattering length density is not constant over the whole scattering size regime.