Hydrogen Storage Properties of Mg-Graphene Composites

To improve the hydrogen uptake and release properties of magnesium (Mg), five weight percent of graphene was added to pre-milled Mg by milling in hydrogen (reaction-involving milling). The hydrogen uptake and release properties of the graphene-added Mg (named Mg-5graphene) were investigated. Premilling of Mg (for 24 h) and then adding graphene by milling in hydrogen (for 30 min) significantly increased the hydrogen uptake and release rates and the quantities of hydrogen absorbed and released for 60 min of the Mg and graphene composite. The activation of Mg-5graphene was completed after the second hydrogen uptake-release cycle (n=2). Mg-5graphene had a high effective hydrogen-storage capacity (quantity of hydrogen absorbed for 60 min) of 5.47 wt% at 593 K in 12 bar H2 at n=3. Mg-5graphene absorbed 0.92 wt% H for 2.5 min, 2.67 wt% H for 10 min, and 5.62 wt% H for 60 min in 12 bar H2 and released 0.25 wt% H for 2.5 min and 4.99 wt% H for 60 min in 1.0 bar H2 at 623 K at n=1. The increase in ID/IG, the ratio of intensities of D and G peaks in Raman spectra, after reaction-involving milling of the pre-milled Mg with graphene, compared with that of the used graphene, suggests that defects and disordering in the graphene were increased. We believe that the generation of stacking fault disorder and formation of turbostratic graphite occurred after milling with the pre-milled Mg, rather than the formation of defects, in graphene.