Craig E. Buckley

Thermodynamic Changes in Mechanochemically Synthesized Magnesium Hydride Nanoparticles

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.

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.

Eutectic melting in metal borohydrides

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.

Concentrating Solar Thermal Heat Storage Using Metal Hydrides

Increased reliance on solar energy conversion technologies will necessarily constitute a major plank of any forward global energy supply strategy. It is possible that solar photovoltaic (PV) technology and concentrating solar thermal (CST) power technology will play roughly equal, but complementary roles by 2050. The ability to increase reliance on CST power technology during this period, however, will be constrained by a number of factors: the large plant sizes dictated by economies of scale, the high associated transmission infrastructure investment cost, and the limitations of current thermal energy storage technologies. Thus, solar technologys main midterm role is seen to be as hybrid solar thermal power plant. The development of low-cost, high-temperature, high-energy density thermal energy storage systems is needed to enable CST plants to be dispatchable and accelerate the deployment of this technology. Thermochemical storage has the best potential to achieve these energy storage requirements and a brief overview of thermochemical energy storage options for CST plants points to high-temperature metal-hydride thermochemical heat energy storage systems. Hydrogen storage systems offer the highest energy storage capacity per volume and are therefore the most likely candidates for achieving the goal of fully dispatchable CST plants. A number of high-temperature metal-hydride thermochemical solar energy storage systems have been proposed and a small number of these systems are currently being investigated and developed. A key component of this work is matching the thermochemical metal-hydride system with a suitable “low-temperature” hydrogen storage material to produce systems that are self-regulating. A summary of the development status of these systems suggests that, despite the technical challenges associated with high-temperature thermochemical energy storage systems, their potential advantages are now seeing development occurring. Although in the early stages, their commercialisation could be fast tracked.

Thermal stability of Li2B12H12 and its role in the decomposition of LiBH4

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 β-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 β- and γ-Li2B12H12 polymorphs and substoichiometric Li2B12H(12-x).

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

A simplified techno-economic model has been used as a screening tool to explore the factors that have the largest impact on the costs of using metal hydrides for concentrating solar thermal storage. The installed costs of a number of paired metal hydride concentrating solar thermal storage systems were assessed. These comprised of magnesium-based (MgH2, Mg2FeH6, NaMgH3, NaMgH2F) high-temperature metal hydrides (HTMH) for solar thermal storage and Ti1.2Mn1.8H3.0 as the low-temperature metal hydride (LTMH) for hydrogen storage. A factored method approach was used for a 200 MWel power plant operating at a plant capacity factor (PCF) of 50% with 7 hours of thermal storage capacity at full-load. In addition, the hydrogen desorption properties of NaMgH2F have been measured for the first time. It has a practical hydrogen capacity of 2.5 wt% (2.95 wt% theoretical) and desorbs hydrogen in a single-step process above 478 °C and in a two-step process below 478 °C. In both cases the final decomposition products are NaMgF3, Na and Mg. Only the single-step desorption is suitable for concentrating solar thermal storage applications and has an enthalpy of 96.8 kJ mol−1 H2 at the midpoint of the hydrogen desorption plateau. The techno-economic model showed that the cost of the LTMH, Ti1.2Mn1.8H3.0, is the most significant component of the system and that its cost can be reduced by increasing the operating temperature and enthalpy of hydrogen absorption in the HTMH that, in turn, reduces the quantity of hydrogen required in the system for an equivalent electrical output. The result is that, despite the fact that the theoretical thermal storage capacity of NaMgH2F (1416 kJ kg−1) is substantially lower than the theoretical values for MgH2 (2814 kJ kg−1), Mg2FeH6 (2090 kJ kg−1) and NaMgH3 (1721 kJ kg−1), its higher enthalpy and operating temperature leads to the lowest installed cost of the systems considered. A further decrease in cost could be achieved by utilizing metal hydrides with yet higher enthalpies and operating temperatures or by finding a lower cost option for the LTMH.

Characterization of the charging techniques used to introduce hydrogen in aluminum

Abstract Aluminum foils and single crystals of varying thickness and purity were charged with hydrogen using gas plasma, electrochemical and chemical methods. The concentrations of hydrogen introduced were monitored by gas extraction and prompt γ-activation analysis measurements. X-ray diffraction measurements indicated that within experimental error there was either a small lattice contraction or a zero change in lattice parameter after charging. It was found that during cathodic and chemical charging an Al(OH)3 layer formed on the surface. Extensive experiments revealed that unless the surface layer formed during the charging process was removed, the concentration of H measured with either analysis method was erroneously high. The plasma charged samples do not form an Al(OH)3 layer on the surface, but instead form H–vacancy complexes at the surface which diffuse into the volume and then cluster to form H2 bubbles. The structure of the hydrogen solutes introduced by the charging methods is discussed and the diffusivity of a hydrogen–vacancy complex at 300 K is estimated.

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.

Delamination and re-assembly of surfactant-containing Li/Al layered double hydroxides

Exchange of the chloride anion intercalated in [LiAl2(OH)6]Cl.nH2O with a range of surfactants is reported. Attempts to delaminate (or exfoliate) the surfactant-exchanged intercalates, where the surfactant was an alkyl sulfate, were unsuccessful. In contrast, delamination of the layered double hydroxides [LiAl2(OH)6][C12H25C6H4SO3.nH2O] and [LiAl2(OH)6][C8H17C6H4SO3.nH2O] was successful. The necessity of the alkyl chain of the surfactants was demonstrated by the failure of [LiAl2(OH)6][CH3C6H4SO3.nH2O] to delaminate. The delamination of the unique Li/Al LDH is thus found to be dependent on the guest surfactant structure in terms of both chain length and head group moiety.

Characterization of H defects in the aluminium- hydrogen system using small-angle scattering techniques

Aluminium foils (99.99% purity) and single crystals (99.999% purity) were charged with hydrogen using a gas plasma method and electrochemical methods, resulting in the introduction of a large amount of hydrogen. X-ray diffraction measurements indicated that within experimental error there was a zero change in lattice parameter after plasma charging. This result is contradictory to almost all other face-centred cubic (f.c.c.) materials, which exhibit a lattice expansion when the hydrogen enters the lattice interstitially. It is hypothesized that the hydrogen does not enter the lattice as an interstitial solute, but instead forms an H–vacancy complex at the surface that diffuses into the volume and then clusters to form H2 bubbles. Small- and ultra-small-angle neutron scattering (SANS, USANS) and small-angle X-ray scattering (SAXS) were primarily employed to study the nature and agglomeration of the H–vacancy complexes in the Al–H system. The SAXS results were ambiguous owing to double Bragg scattering, but the SANS and USANS investigation, coupled with results from inelastic neutron scattering, and transmission and scanning electron microscopy, revealed the existence of a large size distribution of hydrogen bubbles on the surface and in the bulk of the Al–H system. The relative change in lattice parameter is calculated from the pressure in a bubble of average volume and is compared with the experimentally determined value.