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1.
Phys Chem Chem Phys ; 2020 Feb 13.
Artigo em Inglês | MEDLINE | ID: mdl-32051979

RESUMO

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.

2.
Chem Commun (Camb) ; 55(23): 3410-3413, 2019 Mar 14.
Artigo em Inglês | MEDLINE | ID: mdl-30839031

RESUMO

Solvated lithium closo-dodecaborate, Li2B12H12 with tetrahydrofuran and acetonitrile, show unexpected melting below 150 °C. This feature has been explored to melt-infiltrate Li2B12H12 in a nanoporous SiO2 scaffold. The ionic conductivity of Li2B12H12·xACN reaches 0.08 mS cm-1 in the liquid state at 150 °C making them suitable as battery electrolytes.

3.
Dalton Trans ; 48(15): 5048-5057, 2019 Apr 09.
Artigo em Inglês | MEDLINE | ID: mdl-30916691

RESUMO

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, ß = 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.

4.
Inorg Chem ; 57(17): 10768-10780, 2018 Sep 04.
Artigo em Inglês | MEDLINE | ID: mdl-30137973

RESUMO

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'- ß-, 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.

5.
Phys Chem Chem Phys ; 20(23): 16266-16275, 2018 Jun 13.
Artigo em Inglês | MEDLINE | ID: mdl-29863201

RESUMO

The hydrogen absorption properties of metal closo-borate/metal hydride composites, M2B10H10-8MH and M2B12H12-10MH, M = Li or Na, are studied under high hydrogen pressures to understand the formation mechanism of metal borohydrides. The hydrogen storage properties of the composites have been investigated by in situ synchrotron radiation powder X-ray diffraction at p(H2) = 400 bar and by ex situ hydrogen absorption measurements at p(H2) = 526 to 998 bar. The in situ experiments reveal the formation of crystalline intermediates before metal borohydrides (MBH4) are formed. On the contrary, the M2B12H12-10MH (M = Li and Na) systems show no formation of the metal borohydride at T = 400 °C and p(H2) = 537 to 970 bar. 11B MAS NMR of the M2B10H10-8MH composites reveal that the molar ratio of LiBH4 or NaBH4 and the remaining B species is 1 : 0.63 and 1 : 0.21, respectively. Solution and solid-state 11B NMR spectra reveal new intermediates with a B : H ratio close to 1 : 1. Our results indicate that the M2B10H10 (M = Li, Na) salts display a higher reactivity towards hydrogen in the presence of metal hydrides compared to the corresponding [B12H12]2- composites, which represents an important step towards understanding the factors that determine the stability and reversibility of high hydrogen capacity metal borohydrides for hydrogen storage.

6.
Inorg Chem ; 57(4): 2103-2110, 2018 Feb 19.
Artigo em Inglês | MEDLINE | ID: mdl-29389120

RESUMO

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.

7.
Phys Chem Chem Phys ; 20(4): 2274-2283, 2018 Jan 24.
Artigo em Inglês | MEDLINE | ID: mdl-29303173

RESUMO

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(HxF1-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(H0.85F0.15)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(H0.43F0.57)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(H0.85F0.15)2 have determined the enthalpy (ΔHdes) to be 73.6 ± 0.2 kJ mol-1 H2 and entropy (ΔSdes) to be 131.2 ± 0.2 J K-1 mol-1 H2, which is slightly lower than MgH2 with ΔHdes of 74.06 kJ mol-1 H2 and ΔSdes = 133.4 J K-1 mol-1 H2. Cycling studies of Mg(H0.85F0.15)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.

8.
Nat Commun ; 8: 15136, 2017 04 26.
Artigo em Inglês | MEDLINE | ID: mdl-28443627

RESUMO

Silver compounds share a rich history in technical applications including photography, catalysis, photocatalysis, cloud seeding and as antimicrobial agents. Here we present a class of silver compounds (Ag2B10H10 and Ag2B12H12) that are semiconductors with a bandgap at 2.3 eV in the green visible light spectrum. The silver boranes have extremely high ion conductivity and dynamic-anion facilitated Ag+ migration is suggested based on the structural model. The ion conductivity is enhanced more than two orders of magnitude at room temperature (up to 3.2 mS cm-1) by substitution with AgI to form new compounds. Furthermore, the closo-boranes show extremely fast silver nano-filament growth when excited by electrons during transmission electron microscope investigations. Ag nano-filaments can also be reabsorbed back into Ag2B12H12. These interesting properties demonstrate the multifunctionality of silver closo-boranes and open up avenues in a wide range of fields including photocatalysis, solid state ionics and nano-wire production.

9.
Chem Soc Rev ; 46(5): 1565-1634, 2017 Mar 06.
Artigo em Inglês | MEDLINE | ID: mdl-28218318

RESUMO

A wide variety of metal borohydrides, MBH4, have been discovered and characterized during the past decade, revealing an extremely rich chemistry including fascinating structural flexibility and a wide range of compositions and physical properties. Metal borohydrides receive increasing interest within the energy storage field due to their extremely high hydrogen density and possible uses in batteries as solid state ion conductors. Recently, new types of physical properties have been explored in lanthanide-bearing borohydrides related to solid state phosphors and magnetic refrigeration. Two major classes of metal borohydride derivatives have also been discovered: anion-substituted compounds where the complex borohydride anion, BH4-, is replaced by another anion, i.e. a halide or amide ion; and metal borohydrides modified with neutral molecules, such as NH3, NH3BH3, N2H4, etc. Here, we review new synthetic strategies along with structural, physical and chemical properties for metal borohydrides, revealing a number of new trends correlating composition, structure, bonding and thermal properties. These new trends provide general knowledge and may contribute to the design and discovery of new metal borohydrides with tailored properties towards the rational design of novel functional materials. This review also demonstrates that there is still room for discovering new combinations of light elements including boron and hydrogen, leading to complex hydrides with extreme flexibility in composition, structure and properties.

10.
Phys Chem Chem Phys ; 18(39): 27545-27553, 2016 Oct 05.
Artigo em Inglês | MEDLINE | ID: mdl-27722466

RESUMO

Metal borides are often decomposition products from metal borohydrides and thus play a role in the reverse reaction where hydrogen is absorbed. In this work, aluminium boride, AlB2, has been investigated as a boron source for the formation of borohydrides under hydrogen pressures of p(H2) = 100 or 600 bar at elevated temperatures (350 or 400 °C). The systems AlB2-MHx (M = Li, Na, Mg, Ca) have been investigated, producing LiBH4, NaBH4 and Ca(BH4)2, whereas the formation of Mg(BH4)2 was not observed at T = 400 °C and p(H2) = 600 bar. The formation of the metal borohydrides is confirmed by powder X-ray diffraction and infrared spectroscopy and the fraction of boron in AlB2 and M(BH4)x is determined quantitatively by 11B MAS NMR. Hydrogenation for 12 h at T = 350-400 °C and p(H2) = 600 bar leads to the formation of substantial amounts of LiBH4 (38.6 mol%), NaBH4 (83.0 mol%) and Ca(BH4)2 (43.6 mol%).

11.
Phys Chem Chem Phys ; 17(41): 27328-42, 2015 Nov 07.
Artigo em Inglês | MEDLINE | ID: mdl-26418174

RESUMO

Designing safe, compact and high capacity hydrogen storage systems is the key step towards introducing a pollutant free hydrogen technology into a broad field of applications. Due to the chemical bonds of hydrogen-metal atoms, metal hydrides provide high energy density in safe hydrogen storage media. Reactive hydride composites (RHCs) are a promising class of high capacity solid state hydrogen storage systems. Ca(BH4)2 + MgH2 with a hydrogen content of 8.4 wt% is one of the most promising members of the RHCs. However, its relatively high desorption temperature of ∼350 °C is a major drawback to meeting the requirements for practical application. In this work, by using NbF5 as an additive, the dehydrogenation temperature of this RHC was significantly decreased. To elucidate the role of NbF5 in enhancing the desorption properties of the Ca(BH4)2 + MgH2 (Ca-RHC), a comprehensive investigation was carried out via manometric measurements, mass spectrometry, Differential Scanning Calorimetry (DSC), in situ Synchrotron Radiation-Powder X-ray Diffraction (SR-PXD), X-ray Absorption Spectroscopy (XAS), Anomalous Small-Angle X-ray Scattering (ASAXS), Scanning and Transmission Electron Microscopy (SEM, TEM) and Nuclear Magnetic Resonance (NMR) techniques.

12.
ChemSusChem ; 8(17): 2789-825, 2015 Sep 07.
Artigo em Inglês | MEDLINE | ID: mdl-26033917

RESUMO

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.


Assuntos
Fontes Geradoras de Energia , Modelos Teóricos , Termodinâmica
13.
Dalton Trans ; 43(35): 13333-42, 2014 Sep 21.
Artigo em Inglês | MEDLINE | ID: mdl-25062344

RESUMO

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 ß = 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.

14.
Phys Chem Chem Phys ; 15(45): 19774-89, 2013 Dec 07.
Artigo em Inglês | MEDLINE | ID: mdl-24141723

RESUMO

A series of monometallic borohydrides and borohydride eutectic mixtures have been investigated during thermal ramping by mass spectroscopy, differential scanning calorimetry, and photography. Mixtures of LiBH4-NaBH4, LiBH4-KBH4, LiBH4-Mg(BH4)2, LiBH4-Ca(BH4)2, LiBH4-Mn(BH4)2, NaBH4-KBH4, and LiBH4-NaBH4-KBH4 all displayed melting behaviour below that of the monometallic phases (up to 167 °C lower). Generally, each system behaves differently with respect to their physical behaviour upon melting. The molten phases can exhibit colour changes, bubbling and in some cases frothing, or even liquid-solid phase transitions during hydrogen release. Remarkably, the eutectic melt can also allow for hydrogen release at temperatures lower than that of the individual components. Some systems display decomposition of the borohydride in the solid-state before melting and certain hydrogen release events have also been linked to the adverse reaction of samples with impurities, usually within the starting reagents, and these may also be coupled with bubbling or frothing of the ionic melt.

15.
Phys Chem Chem Phys ; 15(38): 15825-8, 2013 Oct 14.
Artigo em Inglês | MEDLINE | ID: mdl-23995580

RESUMO

The thermal decomposition of anhydrous Pa3[combining macron] Li2B12H12 was studied in situ by high resolution synchrotron X-ray diffraction. A first-order phase transition can be observed at 355 °C where the unit cell volume expands by ca. 8.7%. The expanded ß-Li2B12H12 polymorph simultaneously decomposes to a hydrogen poor γ-Li2B12H12-x phase. Expansion of the unit cell across the discontinuity is consistent with reorientational motion of B12H12(2-) anions, and the presence of a frustrated Li(+) lattice indicating Li ion conduction.

16.
J Am Chem Soc ; 135(18): 6930-41, 2013 May 08.
Artigo em Inglês | MEDLINE | ID: mdl-23581497

RESUMO

The purpose of this study is to compare the thermal and structural stability of single phase Li2B12H12 with the decomposition process of LiBH4. We have utilized differential thermal analysis/thermogravimetry (DTA/TGA) and temperature programmed desorption-mass spectroscopy (TPD-MS) in combination with X-ray diffraction (XRD) and Fourier transform infrared (FTIR) spectroscopy to study the decomposition products of both LiBH4 and Li2B12H12 up to 600 °C, under both vacuum and hydrogen (H2) backpressure. We have synthesized highly pure single phase crystalline anhydrous Li2B12H12 (Pa-3 structure type) and studied its sensitivity to water and the process of deliquescence. Under either vacuum or H2 backpressure, after 250 °C, anhydrous Li2B12H12 begins to decompose to a substoichiometric Li2B12H12-x composition, which displays a very broad diffraction halo in the d-spacing range 5.85-7.00 Å, dependent on the amount of H released. Aging Pa-3 Li2B12H12 under 450 °C/125 bar H2 pressure for 24 h produces a previously unobserved well-crystallized ß-Li2B12H12 polymorph, and a nanocrystalline γ-Li2B12H12 polymorph. The isothermal release of hydrogen pressure from LiBH4 along the plateau and above the melting point (Tm = 280 °C) initially results in the formation of LiH and γ-Li2B12H12. The γ-Li2B12H12 polymorph then decomposes to a substoichiometric Li2B12H(12-x) composition. The Pa-3 Li2B12H12 phase is not observed during LiBH4 decomposition. Decomposition of LiBH4 under vacuum to 600 °C produces LiH and amorphous B with some Li dissolved within it. The lack of an obvious B-Li-B or B-H-B bridging band in the FTIR data for Li2B12H(12-x) suggests the H poor B12H(12-x) pseudo-icosahedra remain isolated and are not polymerized. Li2B12H(12-x) is persistent to at least 600 °C under vacuum, with no LiH formation observable and only a ca. d = 7.00 Å halo remaining. By 650 °C, Li2B12H(12-x) is finally decomposed, and amorphous B can be observed, with no LiH reflections. Further studies are required to clarify the structural symmetry of the ß- and γ-Li2B12H12 polymorphs and substoichiometric Li2B12H(12-x).

17.
J Am Chem Soc ; 132(14): 5077-83, 2010 Apr 14.
Artigo em Inglês | MEDLINE | ID: mdl-20307102

RESUMO

The thermodynamic properties of magnesium hydride nanoparticles have been investigated by hydrogen decomposition pressure measurements using the Sieverts technique. A mechanochemical method was used to synthesize MgH(2) nanoparticles (down to approximately 7 nm in size) embedded in a LiCl salt matrix. In comparison to bulk MgH(2), the mechanochemically produced MgH(2) with the smallest particle size showed a small but measurable decrease in the decomposition reaction enthalpy (DeltaH decrease of 2.84 kJ/mol H(2) from DeltaH(bulk) = 74.06 +/- 0.42 kJ/mol H(2) to DeltaH(nano) = 71.22 +/- 0.49 kJ/mol H(2)). The reduction in DeltaH matches theoretical predictions and was also coupled with a similar reduction in reaction entropy (DeltaS decrease of 3.8 J/mol H(2)/K from DeltaS(bulk) = 133.4 +/- 0.7 J/mol H(2)/K to DeltaS(nano) = 129.6 +/- 0.8 J/mol H(2)/K). The thermodynamic changes in the MgH(2) nanoparticle system correspond to a drop in the 1 bar hydrogen equilibrium temperature (T(1 bar)) by approximately 6 degrees C to 276.2 +/- 2.4 degrees C in contrast to the bulk MgH(2) system at 281.8 +/- 2.2 degrees C. The reduction in the desorption temperature is less than that expected from theoretical studies due to the decrease in DeltaS that acts to partially counteract the effect from the change in DeltaH.


Assuntos
Hidrogênio/química , Magnésio/química , Nanopartículas/química , Termodinâmica
18.
Chemistry ; 15(23): 5661-5, 2009 Jun 02.
Artigo em Inglês | MEDLINE | ID: mdl-19396886

RESUMO

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.


Assuntos
Curcumina/administração & dosagem , Sistemas de Liberação de Medicamentos , Compostos Férricos/síntese química , Dióxido de Silício/química , Compostos Férricos/química , Nanopartículas/uso terapêutico , Água
19.
Langmuir ; 23(24): 11986-90, 2007 Nov 20.
Artigo em Inglês | MEDLINE | ID: mdl-17949016

RESUMO

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.


Assuntos
Cobalto/química , Cobre/química , Compostos Macrocíclicos/química , Metenamina/química , Micelas , Compostos Organometálicos/química , Tensoativos/química , Microscopia Eletrônica de Transmissão , Porosidade , Espalhamento a Baixo Ângulo , Dióxido de Silício/química , Propriedades de Superfície
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