▎ 摘　　要

The storage of H-2 molecules was studied theoretically on charged and uncharged Mg decorated graphene surfaces using density-functional theory and by incorporating the van der Waals (vdW) interactions. We found that an increase in the number of Mg atoms and H-2 molecule increases the net interaction of the hydrogen molecule with the surface. The Mg-Gr(+) has the hydrogen storage capacity of up to nine H-2 molecules, with the average adsorption energy of -0.134 eV/H-2. Also, we found that hydrogen molecules play an important role in the interaction between the graphene surface and the Mg atom. The charge density difference analysis showed that electron transfer occurs from H-2 molecules to Mg atom in uncharged system. However, the Bader charge analysis showed that the positive charges in the Mg-Gr(+) and nH(2)-Mg-Gr(+) systems are concentrated on the Mg atom. When the number of H-2 molecules reaches more than 4, the charge transfer instead occurs from the Mg atom to H-2 molecules as well as to the graphene surface. This results in better interaction between the Mg atom and the Gr(+) surface. (C) 2018 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.