Solid-state hydrogen storage in Hydralloy–graphite composites

Hydrogen-based power systems require safe, efficient and robust hydrogen storage solutions. In this regard, metal hydrides become increasingly important because of their extremely high volumetric hydrogen capacity and their moderate operation pressures. The loading and unloading dynamics of hydride-based hydrogen tanks is mainly influenced by the intrinsic hydrogen sorption kinetics of the storage material as well as by the heat and gas transport properties of the hydride bed.In this contribution, pelletized composites of the room-temperature hydrogen storage material Hydralloy C52 (AB2-type) with expanded natural graphite (ENG) are discussed in view of high-dynamic hydrogen solid-state storage applications. Powdery Hydralloy C52 is blended with up to 12.5 wt.% ENG. The blend is pelletized at compaction pressures up to 600 MPa. The Hydralloy–ENG pellets exhibit an increased effective thermal conductivity and provide an increased volumetric H2 storage capacity compared to loose powders. The hydrogenation behavior at different temperatures and for various hydrogenation–dehydrogenation cycles is discussed. Furthermore, the stability of the pellets throughout cyclic hydrogenation is evaluated. High gas permeability in radial direction and sufficient thermal conductivity in combination with a stable pellet structure underline the potential of Hydralloy–ENG composites for hydrogen storage applications with high loading dynamics.

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► Cyclically stable pellets of Hydralloy–graphite blends were prepared.
► Very fast (de-)hydrogenation of Hydralloy–graphite pellets are demonstrated.
► Thermal conductivity and porosity are controlled via graphite content.
► High gas permeabilities and heat conductivities in radial direction are found.