Characterization of Mg-Al alloys with Graphene Additives for Hydrogen Storage

Magnesium hydride, a high hydrogen storage capacity with low sorption kinetic below 623K, can be
destabilized by alloying with Al. Depending on the composition, the alloy hydrogenates in multi-step reactions and the hydrogenation-dehydrogenation reactions are reversible. The theoretical hydrogen capacity of Mg17Al12 is 4.4 wt.% H2. The air-exposure resistance and activation kinetics of the Mg-Al system can be improved by adding graphite. In this study, the effect of graphene addition up to 15 wt.% in the Mg60Al40 alloys on morphology, hydrogenation reaction, and capacity of hydrogen storage was investigated at different mixing times. The Microstructure of the as-milled samples was explored using a scanning electron microscope (SEM). Hydrogen absorption was investigated using a SETARAM apparatus at 623 K and 20 bar. Their phases were analyzed using X-Ray diffraction (XRD). The morphology of the as-milled powder varied with the addition of the graphene which dramatically changed the activation kinetics. The hydrogenation kinetics increased with graphene additions. The hydrogen capacity was optimized at 15-minute mixing with graphene. The longer the mixing time, the slower the kinetics. Mixing with 10 wt.% graphenes for 15 minutes, the Mg60Al40 alloy obtained the fastest activation kinetics. The hydrogen capacity reached 2.7 wt.% after two-hour hydrogenation.