The storage of hydrogen in metal alloys as an alternative to hydrogen storage in pressurized or liquid form has the advantage of high volumetric storage capacity and less complex storage systems due to lower pressure and moderate temperature conditions. The later leads to an improved safety and reduced cost of the storage vessel. However, when considering their utilization in hydrogen storage tanks, swelling-induced stress and heat management are challenges that still require to be addressed. Several strategies have been published in the past to address these problems, however it can be challenging to scale them up. In this work, we propose an easily scalable approach to overcome these drawbacks. The commercially available AB2 room-temperature metal alloy Hydralloy C5 was modified by applying a wash coating-like metho-dology. The surface of the metal alloy was coated with a mixture of a conductive material like expanded natural graphite (ENG) or aluminum and the elastomeric ethylene-vinyl acetate copolymer (EVA). The performance of this modified metal alloy was investigated by in situ measurement of hydrogen capacity, heat dissipation and swelling-induced stress during 50 hydrogenation/dehydrogenation cycles. The coated metal alloy maintained a satisfactory hydrogen capacity with slightly improved heat dissipation. The swelling-induced stress behavior of the treated material was greatly improved. Especially the addition of a mixture of 10 wt% ENG and 10 wt% EVA allowed to completely compensate for the swelling-induced stress during hydrogenation.(c) 2023 Elsevier B.V. All rights reserved.

Renewable energies, such as photovoltaic and wind power, are characterized by intermittent production. For this reason, the storage of energy is necessary for an efficient management of renewable energy. Among several solutions proposed, the use of hydrogen as energy carrier is under investigation.1,2 Compared to batteries, hydrogen allows storing large amounts of energy in small volumes, over long-time, i.e. no self-discharge issues, with low environmental impact.3 Hydrogen can be produced using renewable energies by electrolysis, which splits water into hydrogen and oxygen. The produced hydrogen is stored, and it can then be converted back into electrical energy by means of a fuel cell. Hydrogen can be absorbed in the form of a metallic hydride under mild conditions, i.e. close to room temperatures and atmospheric pressure. This solution ensures safe storage and reduces the volume required for storing even large quantities of hydrogen. Hydrogen storage remains a challenge and the HyCARE project, supported by the European Fuel Cells and Hydrogen Joint Undertaking (grant agreement No 826352), plans to address it. The project involves the production of 5 tons of metal alloy, which will fill special containers for large-scale stationary hydrogen storage. The thermal management of the plant will take place through an innovative approach, making use of phase change materials, significantly increasing the efficiency of the process. The amount of stored hydrogen will be at least 50 kg, which will represent the highest quantity ever stored in Europe with this technique. The consortium is led by the University of Turin, together with the Environment Park, and sees the presence of a large metallic powder producer (GKN Sinter Metals) and the French energy multinational company Engie, which will make its site in Paris available for the demonstration. The plant will be built by two small-medium enterprises, a German (Stuhff) and an Italian (Tecnodelta) one. Four research centers will also support the project: the Italian Bruno Kessler Foundation of Trento, the French CNRS, the Helmholtz-Zentrum Geesthacht in Germany and the Norwegian Institute for Energy Technology at Kjeller. The lab-scale experimental studies and theoretical modelling on metal hydrides, performed last years in European laboratories, will find a promising application at a large scale. The concept and the research behind the project will be presented and discussed. References (1) Moller, K. T.; Jensen, T. R.; Akiba, E.; Li, H.-W. Hydrogen - A Sustainable Energy Carrier. Prog. Nat. Sci. Mater. Int. 2017, 27 (1), 34–40. https://doi.org/10.1016/j.pnsc.2016.12.014. (2) Jensen, C.; Akiba, E.; Li, H.-W. Hydrides: Fundamentals and Applications. Energies 2016, 9 (4), 308. https://doi.org/10.3390/en9040308. (3) Belmonte, N.; Girgenti, V.; Florian, P.; Peano, C.; Luetto, C.; Rizzi, P.; Baricco, M. A Comparison of Energy Storage from Renewable Sources through Batteries and Fuel Cells: A Case Study in Turin, Italy. Int. J. Hydrogen Energy 2016, 41 (46), 21427–21438. https://doi.org/10.1016/j.ijhydene.2016.07.260.

New insights into the reaction pathways of different potassium/magnesium amide-hydride based systems are discussed. In situ SR-PXD experiments were for the first time performed in order to reveal the evolution of the phases connected with the hydrogen releasing processes. Evidence of a new K-N-H intermediate is shown and discussed with particular focus on structural modification. Based on these results, a new reaction mechanism of amide-hydride anionic exchange is proposed.

The production cost of materials for hydrogen storage is one of the major issues to be addressed in order to consider them suitable for large scale applications. In the last decades several authors reported on the hydrogen sorption properties of Mg and Mg-based systems. In this work magnesium industrial wastes of AZ91 alloy and Mg-10 wt.% Gd alloy are used for the production of hydrogen storage materials. The hydrogen sorption properties of the alloys were investigated by means of volumetric technique, in situ synchrotron radiation powder X-ray diffraction (SR-PXD) and calorimetric methods. The measured reversible hydrogen storage capacity for the alloys AZ91 and Mg-10 wt.% Gd are 4.2 and 5.8 wt.%, respectively. For the Mg-10 wt.% Gd alloy, the hydrogenated product was also successfully used as starting reactant for the synthesis of Mg(NH2)(2) and as MgH2 substitute in the Reactive Hydride Composite (RHC) 2LiBH(4) + MgH2. The results of this work demonstrate the concrete possibility to use Mg alloy wastes for hydrogen storage purposes. (C) 2014 Elsevier B.V. All rights reserved.

A reactive hydride composite (RHC) with initial composition 3CaH2 + 4MgB2 + CaF2 was studied by in situ synchrotron radiation powder X-ray diffraction (SR-PXD) and X-ray absorption near edge structure (XANES) at the B K-edge and at the Ca K-edge. The hydrogenation reaction proceeds by an unknown intermediate. No evidence of intermediates was observed during the dehydrogenation reaction. B and Ca K-edge XANES results hint to a closed interaction of CaF2 and Ca(BH4)2. The main function of CaF2 in the 3CaH2 + 4MgB2 + CaF2 RHC is as a dopant for the hydrogenation and dehydrogenation reactions.

The hydrogenation behavior of 3CaH2+4MgB2+CaF2 composite was studied by manometric measurements, powder X-ray diffraction, differential scanning calorimetry and attenuated total reflection infrared spectroscopy. The maximum observed quantity of hydrogen loaded in the composite was 7.0wt%. X-ray diffraction showed the formation of Ca(BH4)2 and MgH2 after hydrogenation. The activation energy for the dehydrogenation reaction was evaluated by DSC measurements and turns out to be 162±15kJmol−1 H2. This value decreases due to cycling to 116±5kJmol−1 H2 for the third dehydrogenation step. A decrease of ca. 25–50°C in dehydrogenation temperature was observed with cycling. Due to its high capacity and reversibility, this composite is a promising candidate as a potential hydrogen storage material.