A simple solvent-free method to synthesize MgH2 nanoparticles（MgH2NPs） uniformly grown on graphene nanosheets（GNs） has been reported in this paper. Based on the formation of MgH2 by di-n-butylmagnesium(（C4H9）2Mg) thermal decomposition under hydrogen pressure, the GNs were added as matrix to hinder the agglomeration and growing of MgH2NPs. The fabricated MgH2/GNs nanocomposites, in which MgH2 NPs were homogenously growing in the graphene matrix, have been synthesized by the favorable adsorption energy between（C4H9）2Mg and GNs. Resulting from the one-step solvent-free route, the generated MgH2 NPs shows high hydrogen capacity and steady hydriding and dehydriding properties, without the interference of the synthetic medium. At the same time, the size of the fabricated MgH2NPs can be controlled by adjusting the mass ratio of MgH2 to graphene, the various hydrogen pressure and temperature. Attributed to smaller size effect, well uniform distribution of high density MgH2NPs, and the agglomeration blocking ability of graphene,the MgH2/GNs-40 wt% exhibits the favorite hydrogen storage performance.
