▎ 摘　　要

We report a facile solid state method to in situ synthesize highly dispersed MgH2 nanoparticle-graphene nanosheet composites and their improved dehydrogenation/hydrogenation properties. The graphene is used as the support to in situ prepare the MgH2 nanoparticles. The MgH2 nanoparticle-10 wt % graphene nanosheet composites possess the best hydrogen storage properties among Mg-based materials. The onset dehydrogenation temperature of the MgH2 nanoparticle-10 wt % graphene nanosheet composites decreases to 255 degrees C. More importantly, the MgH2 nanoparticle-10 wt % graphene nanosheet composites can release 5.1 wt % hydrogen in 20 min at 325 degrees C. Moreover, the dehydrogenated composites could absorb 5.2 wt % hydrogen in 10 min at 250 degrees C under the hydrogen pressure of 2 MPa. The well-dispersed MgH2 nanoparticles (similar to 3 nm) and the confinement effect of graphene result in the improved hydrogen storage properties. The novel solid state method of in situ synthesizing MgH2 nanoparticles provides a new horizon for designing high performance Mg-based materials.