Powder diffraction methods for studies of borohydride-based energy storage materials

The world today is facing increasing energy demands and a simultaneous demand for cleaner and more environmentally friendly energy technologies. Hydrogen is recognized as a possible renewable energy carrier, but its large-scale utilization is mainly hampered by insufficient hydrogen storage capabilities. In this scenario, powder diffraction has a central position as the most informative and versatile technique available in materials science. This is illustrated in the present review by synthesis, physical, chemical and structural characterisation of novel boron based hydrides for hydrogen storage. Numerous novel BH4- based materials have been investigated during the past few years and this class of materials has a fascinating structural chemistry. The experimental methods presented can be applied to a variety of other material

New type of stonewool (HT fibres) with a higli dissolution rate at pH = 4.5

Α representative, the HT-3 fibre, of a new type of stonewool (HT fibres), characterized by a relatively high content of a lumina and a relatively low content of silica, has recently been tested in-vivo by Bellmann et al. to have a low biopersistence after intratracheal instilladon in rat lungs. Several advantages of this fibre were found: - a half-time T50 which is 2 respectively 4 times lower than that for the reference fibres glasswool and stonewool (after correcting to 1 µm median diameter), - a better ultimate clearance after 18 months, resulting in 3 % remaining for the HT-3 fibre compared to 32 % for normal stonewool, - an effective clearance of fibres with a diameter < 0.5 µm. Fibres with a diameter belonging to this class are generally thought to be those with the highest potency for tumour formadon. The HT fibres have a relatively low in-vitro dissolution rate at p H = 7.5, similar to that of normal stonewool fibres, but a high in-vitro dissolution rate at pH = 4.5. The explanation of the favourable in-vivo properties of t h e HT-3 fibre is based on the recent investigations of the ability of alveolar macrophages to dissolve certain fibres, coupled with the Observation of the high dissolution rate of the HT fibres at the pH value of 4.5 to 5 prevailing inside the macrophages. All HT fibres have been shown t o have comparable, high dissolution rates at pH = 4.5 to 5

Mg–Ti nanoparticles with superior kinetics for hydrogen storage

open5siAcknowledgements The assistance of F. Corticelli and V. Morandi (IMM-CNR, Bologna) during FE-SEM observations is gratefully acknowledged. Part of this work was supported by the COST Action MP1103 “Nanostructured materials for solid-state hydrogen storage”. We are grateful to the beamline I711 at MAXlab, Lund, Sweden for the provision of beamtime.Mg nanoparticles (NPs) with addition of Ti catalysts were synthesised by inert gas condensation and in situ hydrogenation at 150 °C. The NPs size and composition were systematically investigated by scanning electron microscopy, energy dispersive X-ray spectroscopy and powder X-ray diffraction (PXD), while time resolved in situ synchrotron radiation-PXD was used to monitor the mechanism for hydrogen uptake and release at 280 °C. The Mg–Ti NPs reveal activation energies of 68 kJ mol−1 for absorption and 78 kJ mol−1 for desorption by isothermal kinetics analysis, similar to the lowest values reported in the literature for MgH2 using Nb2O5 as a catalyst. Hence, hydrogen desorption (pdes = 8 mbar) and absorption (pabs = 260 mbar) is achieved at 200 °C in ∼2000 s, while keeping 5.3 wt% storage capacity. Thermodynamic data extracted from van ’t Hoff plots reveal unchanged values compared to bulk MgH2. Therefore, the improved hydrogen storage performances are assigned to the enhanced kinetics only.openCalizzi, Marco; Chericoni, Domizia; Jepsen, Lars H.; Jensen, Torben R.; Pasquini, LucaCalizzi, Marco; Chericoni, Domizia; Jepsen, Lars H.; Jensen, Torben R.; Pasquini, Luc

Interplay of NH4+ and BH4- reorientational dynamics in NH4BH4

The reorientational dynamics of ammonium borohydride (NH4BH4) was studied using quasielastic neutron scattering in the temperature interval from 10 to 240 K, which covers both the dynamically ordered and disordered polymorphs of NH4BH4. In the low-temperature (50 K) ordered polymorph of NH4BH4, analysis of the quasielastic neutron scattering data reveals that no reorientational dynamics is present within the probed timescale region of 0.1 to 100 ps. In the high-temperature (50 K) disordered polymorph, the analysis establishes the onset of NH4+ and BH4- dynamics at around 50 and 125 K, respectively. The relaxation time at 150 K for NH4+ is approximately 1 ps, while around 100 ps for BH4- . The NH4+ dynamics at temperatures below 125 K is associated with preferential tetrahedral tumbling motions, where each of the hydrogen atoms in the NH4+ tetrahedron can visit any of the four hydrogen sites, however, reorientations around a specific axis are more frequently occurring (C-2 or C3). At higher temperatures, the analysis does not exclude a possible evolution of the NH4+ dynamics from tetrahedral tumbling to either cubic tumbling, where the hydrogen atoms can visit any of the eight positions corresponding to the corners of a cube, or isotropic rotational diffusion, where the hydrogen atoms can visit any location on the surface of a sphere. The BH4- dynamics can be described as cubic tumbling. The difference in reorientational dynamics between the two ions is related to the difference of the local environment where the dynamically much slower BH4- anion imposes a noncubic environment on the NH4+ cation

Structural and dynamic studies of Pr(11^{11}BH4_{4})3_{3}

Rare earth borohydrides RE (BH4)(3) are studied in the context of energy storage, lumines-cence and magnetic applications. We have investigated the structural behavior of pra-seodymium borohydride Pr ((BH4)-B-11)(3) containing B-11 isotope because of the previously reported negative thermal expansion. Differential scanning calorimetry (DSC), in-situ var-iable temperature synchrotron radiation powder X-ray diffraction (SR-PXD) and infrared studies reveal that Pr ((BH4)-B-11)(3) undergoes to a volume contraction during the phase tran-sition from alpha alpha-Pr ((BH4)-B-11)(3) to rhombohedral r-Pr ((BH4)-B-11)(3) phase upon heating to 493 K. Surprisingly, the phase transition persists upon cooling at room temperature. Vibrational analysis also shows that the stretching frequency of BH4-3; anion does not change upon heating which indicates that the B-H bond length remains constant during the structural phase transition from alpha-Pr ((BH4)-B-11)(3) to r-Pr ((BH4)-B-11)(3) phase. Additionally, the energy barrier of reorientation motion of the BH4- anion in the alpha-phase was estimated to be ca 23 kJ/mol by quasi-elastic neutron scattering (QENS) and Raman spectroscopy. (C) 2021 The Authors. Published by Elsevier Ltd on behalf of Hydrogen Energy Publications LLC