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Abstract: A mechanochemical synthesis process has been used to synthesise alane (AlH3) nanoparticles. The alane is synthesised via a chemical reaction between lithium alanate (LiAlH4) and aluminium chloride (AlCl3) at room temperature within a ball mill and at 77K within a cryogenic mill. The reaction product formed consists of alane nanoparticles embedded within a lithium chloride (LiCl) by-product phase. The LiCl is washed with a solvent resulting in alane nanoparticles which are separated from the by-product phase but are kinetically stabilised by an amorphous particle surface layer. The synthesis of a particular alane structural phase is largely dependent on the milling conditions and two major phases (α, α′) as well as two minor phases (β, γ) have been identified. Ball milling at room temperature can also provide enough energy to allow alane to release hydrogen gas and form aluminium metal nanoparticles. A comparison between XRD and hydrogen desorption results suggest a non-crystalline AlH3 phase is present in the synthesised samples. [Copyright &y& Elsevier]

Abstract: A number of MCM-41 samples were produced with different ageing times and zinc dopant levels. Hydrogen adsorption experiments performed at 77K on pure MCM-41 samples showed a maximum excess wt% uptake of 2.01%. Samples were doped with Zn in the Si:Zn ratio of 50:1, 25:1 and 10:1. These samples showed an increase in -spacing in their XRD patterns, suggestive of Zn incorporation into the structure but resulting in a decrease in long range pore ordering and surface area with increasing Zn content. Two of the three doped samples showed an increase in adsorbed per unit surface area suggestive of increased interaction strength. However, definitive confirmation is difficult due to degradation of the pore structure and surface area. Adsorption at room temperature was minimal, being 0.1wt% or below. [Copyright &y& Elsevier]

Abstract: The Ti0.97Zr0.019V0.439Fe0.097Cr0.045Al0.026Mn1.5 alloy is a hexagonal C14 Laves phase material that reversibly stores hydrogen under ambient temperatures. Structural changes are studied by XRD and SEM with regard to hydrogenation and dehydrogenation cycling at 25, 40 and 60 °C. The average particle size is reduced after hydrogenation and dehydrogenation cycling through decrepitation. The maximum hydrogen capacity at 25 °C is 1.71 ± 0.01 wt. % under 78 bar H2, however the hydrogen sorption capacity decreases and the plateau pressure increases at higher temperatures. The enthalpy (ΔH) and entropy (ΔS) of hydrogen absorption and desorption have been calculated from a van’t Hoff plot as −21.7 ± 0.1 kJ/mol H2 and −99.8 ± 0.2 J/mol H2/K for absorption and 25.4 ± 0.1 kJ/mol H2 and 108.5 ± 0.2 J/mol H2/K for desorption, indicating the presence of a significant hysteresis effect. [Copyright &y& Elsevier]

Abstract: The MgH2 + 0.02Ti-additive system (additives = 35 nm Ti, 50 nm TiB2, 40 nm TiC, <5 nm TiN, 10 × 40 nm TiO2) has been studied by high-resolution synchrotron X-ray diffraction, after planetary milling and hydrogen (H) cycling. TiB2 and TiN nanoparticles were synthesised mechanochemically whilst other additives were commercially available. The absorption kinetics and temperature programmed desorption (TPD) profiles have been determined, and compared to the benchmark system MgH2 + 0.01Nb2O5 (20 nm). TiC and TiN retain their structures after milling and H cycling. The TiB2 reflections appear compressed in d-spacing, suggesting Mg/Ti exchange has occurred in the TiB2 structure. TiO2 is reduced, commensurate with the formation of MgO, however, the Ti is not evident anywhere in the diffraction pattern. The 35 nm Ti initially forms an fcc Mg47.5Ti52.5 phase during milling, which then phase separates and hydrides to TiH2 and MgH2. At 300 °C, the MgH2 + 0.02 (Ti, TiB2, TiC, TiN, TiO2) samples display equivalent absorption kinetics, which are slightly faster than the MgH2 + 0.01Nb2O5 (20 nm) benchmark. All samples are contaminated with MgO from the use of a ZrO2 vial, and display rapid absorption to ca. 90% of capacity within 20 s at 300 °C. TPD profiles of all samples show peak decreases compared to the pure MgH2 milled sample, with many peak profiles displaying bi-modal splitting. TPD measurements on two separate instruments demonstrate that on a 30 min milling time scale, all samples are highly inhomogenous, and samplings from the exact same batch of milled MgH2 + 0.02Ti-additive can display differences in TPD profiles of up to 30 °C in peak maxima. The most efficient Ti based additive cannot be discerned on this basis, and milling times ≫ 30 min are necessary to obtain homogenous samples, which may lead to artefactual benefits, such as reduction in diffusion distances by powder grinding or formation of dense microstructure. For the hydrogen cycled MgH2 + 0.01Nb2O5 system, we observe a face centred cubic Mg/Nb exchanged Mg0.165Nb0.835O phase, which accounts for ca. 60% of the originally added Nb atoms. [Copyright &y& Elsevier]