Behavior of compacted magnesium-based powders for energy-storage applications

Energy storage is one of the main challenges to address in the near future—in particular due to the intermittent energy produced by extensive renewable energy production plants. The use of hydrides for this type of energy storage has many positive aspects. Hydride-based systems consist of absorption and desorption reactions that are strongly exothermic and endothermic, respectively. Heat management in the design of hydrogen storage tanks is an important issue, in order to ensure high-level performance in terms of the kinetics for hydrogen release/uptake and reasonable storage capacity. When loose powder is used, material in the form of pellets should be considered in order to avoid detrimental effects including decreased cycling performance. Moreover, sustainable materials in large-scale hydrogen reactors could be recovered and reused to improve any life cycle analysis of such systems. For these reasons, magnesium hydride was used in this study, as it is particularly suitable for hydrogen storage due to its high H2 storage capacity, reversibility and the low costs. Magnesium hydride was ball-milled in presence of 5 wt % Fe as a catalyst, then compacted with an uniaxial press after the addition of expanded natural graphite (ENG). The materials underwent 45 cycles in a Sievert’s type apparatus at 310◦ C and eight bar, in order to study the kinetics and cycling stability. Scanning electron microscopy was used to investigate microstructural properties and failure phenomena. Together with Rietveld analysis, X-ray diffraction was performed for phase identification and structural information. The pellets demonstrated suitable cycling stability in terms of total hydrogen storage capacity and kinetics.