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Hydrogen as an energy carrier is very versatile in energy storage applications. Developments in novel, sustainable technologies towards a CO2-free society are needed and the exploration of all-solid-state batteries (ASSBs) as well as solid-state hydrogen storage applications based on metal hydrides can provide solutions for such technologies. However, there are still many technical challenges for both hydrogen storage material and ASSBs related to designing low-cost materials with low-environmental impact. The current materials considered for all-solid-state batteries should have high conductivities for Na+, Mg2+ and Ca2+, while Al3+-based compounds are often marginalised due to the lack of suitable electrode and electrolyte materials. In hydrogen storage materials, the sluggish kinetic behaviour of solid-state hydride materials is one of the key constraints that limit their practical uses. Therefore, it is necessary to overcome the kinetic issues of hydride materials before discussing and considering them on the system level. This review summarizes the achievements of the Marie Skłodowska-Curie Actions (MSCA) innovative training network (ITN) ECOSTORE, the aim of which was the investigation of different aspects of (complex) metal hydride materials. Advances in battery and hydrogen storage materials for the efficient and compact storage of renewable energy production are discussed.

To enhance the dehydrogenation/rehydrogenation kinetic behavior of the LiBH 4 −MgH 2 composite system, TiF 4 is used as an additive. The effect of this additive on the hydride composite system has been studied by means of laboratory and advanced synchrotron techniques. Investigations on the synthesis and mechanism upon hydrogen interaction show that the addition of TiF 4 to the LiBH 4 −MgH 2 composite system during the milling procedure leads to the in situ formation of well-distributed nanosized TiB 2 particles. These TiB 2 nanoparticles act as nucleation agents for the formation of MgB 2 upon dehydrogenation process of the hydride composite system. The effect of TiB 2 nanoparticles is maintained upon cycling.

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In this work the effect of a partial replacement of CaH 2 with CaF 2 on the sorption properties of the system CaH 2 + MgB 2 has been studied. The first five hydrogen absorption and four desorption reactions of the CaH 2 + MgB 2 and 3CaH 2 + CaF 2 + 4MgB 2 systems were investigated by means of volumetric measurements, high-pressure differential scanning calorimetric technique (HP-DSC), 11 B and 19 F MAS NMR spectroscopy, and in situ synchrotron radiation powder X-ray diffraction (SR-PXD). It was observed that already during the mixing of the reactants formation of a nonstoichiometric CaF 2−x H x solid solution takes place. Formation of the CaF 2−x H x solid solution sensibly affects the overall hydrogen sorption reactions of the system CaH 2 + MgB 2 .

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.

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