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Intense literature and research efforts have focussed on the exploration of complex hydrides for energy storage applications over the past decades. A focus was dedicated to the determination of their thermodynamic and hydrogen storage properties, due to their high gravimetric and volumetric hydrogen storage capacities, but their application has been limited because of harsh working conditions for reversible hydrogen release and uptake. The present review aims at appraising the recent advances on different complex hydride systems, coming from the proficient collaborative activities in the past years from the research groups led by the experts of the Task 40 “Energy Storage and Conversion Based on Hydrogen” of the Hydrogen Technology Collaboration Programme of the International Energy Agency. An overview of materials design, synthesis, tailoring and modelling approaches, hydrogen release and uptake mechanisms and thermodynamic aspects are reviewed to define new trends and suggest new possible applications for these highly tuneable materials.

This paper aims at addressing the exploitation of solid-state carriers for hydrogen storage, with attention paid both to the technical aspects, through a wide review of the available integrated systems, and to the social aspects, through a preliminary overview of the connected impacts from a gender perspective. As for the technical perspective, carriers to be used for solid-state hydrogen storage for various applications can be classified into two classes: metal and complex hydrides. Related crystal structures and corresponding hydrogen sorption properties are reviewed and discussed. Fundamentals of thermodynamics of hydrogen sorption evidence the key role of the enthalpy of reaction, which determines the operating conditions (i.e., temperatures and pressures). In addition, it rules the heat to be removed from the tank during hydrogen absorption and to be delivered to the tank during hydrogen desorption. Suitable values for the enthalpy of hydrogen sorption reaction for operating conditions close to ambient (i.e., room temperature and 1–10 bar of hydrogen) are close to 30 kJ·molH2−1. The kinetics of the hydrogen sorption reaction is strongly related to the microstructure and to the morphology (i.e., loose powder or pellets) of the carriers. Usually, the kinetics of the hydrogen sorption reaction is rather fast, and the thermal management of the tank is the rate-determining step of the processes. As for the social perspective, the paper arguments that, as it occurs with the exploitation of other renewable innovative technologies, a wide consideration of the social factors connected to these processes is needed to reach a twofold objective: To assess the extent to which a specific innovation might produce positive or negative impacts in the recipient socioeconomic system and, from a sociotechnical perspective, to explore the potential role of the social components and dynamics in fostering the diffusion of the innovation itself. Within the social domain, attention has been paid to address the underexplored relationship between the gender perspective and the enhancement of hydrogen-related energy storage systems. This relationship is taken into account both in terms of the role of women in triggering the exploitation of hydrogen-based storage playing as experimenter and promoter, and in terms of the intertwined impact of this innovation in their current conditions, at work, and in daily life.

The formation, structure and deuterium desorption properties of Mg 2 fe x co (1−x) D y (0 ≤ x ≤ 1 and 5 ≤ y ≤ 6) complex hydrides were investigated. The synthesis was carried out by reactive ball milling, using a mixture of powders of the parent elements in D 2 atmosphere. The formation of quaternary deuterides was identified from Rietveld refinements of powder X-Ray diffraction and powder neutron diffraction patterns, and from infrared attenuated total reflectance analysis. It was observed that the crystal structure of deuterides depends on the transition metal fraction. For Co-rich compositions, i.e. up to x = 0.1, hydrides have the tetragonal distorted CaF 2-type structure (space group P4/nmm) of Mg 2 coD 5 at room temperature. For Fe-rich compositions, i.e. x ≥ 0.5, a cubic hydride is observed, with the same K 2 ptcl 6-type structure (space group Fm3m) as Mg 2 feD 6 and as Mg 2 coD 5 at high temperatures. for x = 0.3, both the cubic and the tetragonal deuterides are detected. Differential scanning calorimetry coupled with thermogravimetric and temperature programmed desorption analyses show rather similar deuterium desorption properties for all samples, without significant changes as a function of composition. Finally, hydrogen sorption experiments performed for Mg 2 fe 0.5 co 0.5 H 5.5 at 30 bar of H 2 and 673 K showed reversible reactions, with good kinetic for both absorption and desorption of hydrogen. Hydrogen is a promising energy carrier, but technologies for its storage must be improved for its use in a large scale. The purpose of research on hydrogen storage is to achieve high gravimetric and volumetric capacities at mild pressure and temperature conditions. In this regard, hydrogen storage in hydrides is particularly favourable 1. Mg is an attractive hydrogen storage material, due to its low cost and high gravimetric (7.7 H 2 wt.%) and volumetric (110 gH 2 l −1) capacity in MgH 2. However, MgH 2 is a rather stable hydride and its desorption temperature is too high (>573 K) for most practical applications. To reduce the desorption temperature and increase the kinetics of both absorption and desorption, different strategies have been investigated, such as the introduction of defects, the reduction of particles size (e.g. with mechanochemical techniques) and the use of additives (e.g. 3d transition metals and their oxides) 2. Mg-based hydrides containing 3d transition metals (TM), e.g. Ni, Fe and Co, have shown lower hydrogen sorption temperature and improved kinetics, compared to MgH 2. Mg 2 FeH 6 and Mg 2 CoH 5 have high gravimetric (5.6 and 4.5 H 2 wt.%, respectively) 3 and volumetric (150 and 110 gH 2 l −1 , respectively) capacity 4. The crystal structure of both these ternary hydrides is based on the formation of complex anions obeying the 18-electron rule and with a strong covalent bond between TM and hydrogen. In Mg 2 FeH 6 , the octahedral complex anion [FeH 6 ] 4− is surrounded by eight Mg 2+ in a cubic rearrangement. The crystal structure is a cubic K 2 PtCl 6-type (space group Fm3m), with un...

Recently, the industrial and public interest in hydrogen technologies has strongly risen, since hydrogen is the ideal means for medium to long term energy storage, transport and usage in combination with renewable and green energy supply. Therefore, in a future energy system the production, storage and usage of green hydrogen is a key technology. Hydrogen is and will in future be even more used for industrial production processes as reduction agent or for the production of synthetic hydrocarbons, especially in the chemical industry and refineries. Under certain conditions material based systems for hydrogen storage and compression offer advantages over the classical systems based on gaseous or liquid hydrogen. This includes in particular lower maintenance costs, higher reliability and safety. Hydrogen storage is possible at pressures and temperatures much closer to ambient conditions. Hydrogen compression is possible without any moving parts and only by using waste heat. In this paper, the newest developments of hydrogen carriers for storage and compression are summarized. In addition, an overview of the different research activities in this field are given.

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This paper aims at addressing the exploitation of solid-state carriers for hydrogen storage, with attention paid both to the technical aspects, through a wide review of the available integrated systems, and to the social aspects, through a preliminary overview of the connected impacts from a gender perspective. As for the technical perspective, carriers to be used for solid-state hydrogen storage for various applications can be classified into two classes: metal and complex hydrides. Related crystal structures and corresponding hydrogen sorption properties are reviewed and discussed. Fundamentals of thermodynamics of hydrogen sorption evidences the key role of the enthalpy of reaction, which determines the operating conditions (i.e. temperatures and pressures). In addition, it rules the heat to be removed from the tank during hydrogen absorption and to be delivered to the tank during hydrogen desorption. Suitable values for the enthalpy of hydrogen sorption reaction for operating conditions close to ambient (i.e. room temperature and 1-10 bar of hydrogen) are close to 30 kJ·molH2 1. The kinetics of hydrogen sorption reaction is strongly related to the microstructure and to the morphology (i.e. loose powder or pellets) of the carriers. Usually, kinetics of hydrogen sorption reaction is rather fast, and the thermal management of the tank is the rate determining step of the processes. As for the social perspective, various scenarios for the applications in different socio-economic contexts of solid-state hydrogen storage technologies are described. As it occurs with the exploitation of other renewables innovative technologies, a wide consideration of the social factors connected to these processes is needed to assess the extent to which a specific innovation might produce positive or negative impacts in the recipient socio-economic system and to explore the potential role of the social components and dynamics in fostering the diffusion of the innovation itself. Attention has been addressed to the gender perspective, in view of the enhancement of hydrogen-related energy storage systems, intended both in terms of the role of women in triggering the exploitation of hydrogen-based storage as well as to the impact of this innovation in their current conditions, at work and in daily life.