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• Determination of a reaction kinetic model of the de- / hydrogenation of recycled Mg based waste material. • Scaled-up hydrogenation experiments with in-house build autoclave at different temperature conditions. • Development of a validated simulation model that provides perfectly consistent results with experimental data. With the increased use of renewable energy sources, the need to store large amounts of energy will become increasingly important in the near future. A cost efficient possibility is to use the reaction of recycled Mg waste with hydrogen as thermo-chemical energy storage. Owing to the high reaction enthalpy, the moderate pressure and appropriate temperature conditions, the broad abundance and the recyclability, the Mg/Al alloy is perfectly suitable for this purpose. As further development of a previous work, in which the performance of recycled Mg/Al waste was presented, a kinetic model for hydro- and dehydrogenation is derived in this study. Temperature and pressure dependencies are determined, as well as the rate limiting step of the reaction. First experiments are carried out in an autoclave with a scaled-up powder mass, which is also used to validate the model by simulating the geometry with the scaled-up experiments at different conditions. [ABSTRACT FROM AUTHOR]

Abstract: Magnesium hydride is considered to be one of the most interesting alternatives for the reversible storage of hydrogen. It is abundant, inexpensive, easy to handle, environmentally benign and exhibits a high hydrogen storage capacity of up to 7.6 wt.%. Furthermore, nanocrystalline Mg powder prepared by high energy ball milling and the addition of suitable catalysts shows very fast absorption and desorption kinetics. The thermal stability of the nanocrystalline microstructure as well as the respective sorption kinetics of ball-milled MgH2 with or without 0.5 mol% Nb2O5 as catalyst have been investigated after cycling and annealing at the technically relevant temperatures between 300 and 400  C. While kinetics for pure MgH2 slows down substantially already after a few cycles at 300  C, MgH2 with Nb2O5 catalyst still shows fast sorption kinetics after annealing up to 370  C. At higher temperatures, the kinetics for the catalyzed material also breaks down, which is attributed to a deterioration of the catalyst. Continuous coarsening of the microstructure during annealing leads to an increased fraction of the storage capacity that can only be recharged at a slower rate. This is discussed in terms of retarded growth conditions for the MgH2 phase. [Copyright &y& Elsevier]

Abstract Magnesium hydride owns the largest share of publications on solid materials for hydrogen storage. The "Magnesium group" of international experts contributing to IEA Task 32 "Hydrogen Based Energy Storage" recently published two review papers presenting the activities of the group focused on magnesium hydride based materials and on Mg based compounds for hydrogen and energy storage. This review article not only overviews the latest activities on both fundamental aspects of Mg-based hydrides and their applications, but also presents a historic overview on the topic and outlines projected future developments. Particular attention is paid to the theoretical and experimental studies of Mg-H system at extreme pressures, kinetics and thermodynamics of the systems based on MgH 2 , nanostructuring, new Mg-based compounds and novel composites, and catalysis in the Mg based H storage systems. Finally, thermal energy storage and upscaled H storage systems accommodating MgH 2 are presented. Highlights • Historical overview of Mg-based hydrides. • Nanostructured Mg-based H storage materials prepared by mechanical alloying and reactive ball milling. • Thermodynamics and kinetics for Mg-based hydrides. • Catalysis in Mg-H system. • Mg-H system at high pressures: theoretical and experimental studies. [ABSTRACT FROM AUTHOR]

Abstract In the past decades, complex hydrides and complex hydrides-based materials have been thoroughly investigated as materials for energy storage, owing to their very high gravimetric and volumetric hydrogen capacities and interesting cation and hydrogen diffusion properties. Concerning hydrogen storage, the main limitations of this class of materials are the high working temperatures and pressures, the low hydrogen absorption and desorption rates and the poor cyclability. In the past years, research in this field has been focused on understanding the hydrogen release and uptake mechanism of the pristine and catalyzed materials and on the characterization of the thermodynamic aspects, in order to rationally choose the composition and the stoichiometry of the systems in terms of hydrogen active phases and catalysts/destabilizing agents. Moreover, new materials have been discovered and characterized in an attempt to find systems with properties suitable for practical on-board and stationary applications. A significant part of this rich and productive activity has been performed by the research groups led by the Experts of the International Energy Agreement Task 32, often in collaborative research projects. The most recent findings of these joint activities and other noteworthy recent results in the field are reported in this paper. Highlights • New borohydrides are described concerning the chemical and structural properties. • The H 2 mechanism in innovative RHCs and the use of original catalysts are evidenced. • The ionic liquids' action on H 2 production and release by borohydrides is detailed. • The use of metal hydrides as catalysts for (de)hydrogenation reactions is explored. • Original solubility data in hydrides systems in solid and liquid state are presented. [ABSTRACT FROM AUTHOR]

Abstract: Reactive Hydride Composites (RHCs), ball-milled composites of two or more different hydrides, are suggested as an alternative for solid state hydrogen storage. In this work, dehydrogenation of 2NaBH4 + MgH2 system under vacuum was investigated using complementary characterization techniques. At first, thermal programmed desorption of as-milled composite and single compounds was used to identify the temperature range of hydrogen release. RHC samples annealed at various temperatures up to 500 °C were characterized by X-ray diffraction, infrared spectroscopy and scanning electron microscopy. It was found that the dehydrogenation reaction under vacuum is likely to proceed as follows: 2NaBH4 + MgH2 (>250 °C) → 2NaBH4 + 1/2MgH2 + 1/2Mg + 1/2H2 (>350 °C) ↔ 3/2NaBH4 + 1/4MgB2 + 1/2NaH + 3/4Mg + 7/4H2 (>450 °C) → 2Na + B + 1/2Mg + 1/2MgB2 + 5H2. In addition, presence of NaMgH3 phase suggests the occurrence of secondary reactions. [Copyright &y& Elsevier]

Abstract: In this work, the synthesis of Mg87Ni10Al3 hydride by reactive ball milling under H2 atmosphere is presented. Reactive milling under hydrogen induces the conversion of Mg into nanocrystalline MgH2 (final crystallite sizes 8 nm). The percentage of the hydride increases with the milling time and after 20 h of mechanical treatment the reaction is complete. Only at longer milling time, when a high conversion degree of Mg into the hydride is reached, the reaction with Ni to form Mg2NiH4 is observed. Thermal analysis shows that, for the shorter milling time, the decomposition of the hydride starts at 200  C, but the stability of the hydride slightly increases with increasing milling time. Fast absorption–desorption kinetics is obtained at 300  C. [Copyright &y& Elsevier]