Metal (Li, Al, Ca and Ti) absorbed graphene with defects for hydrogen storage: first-principles calculations

The characteristics of Li, Al, Ca and Ti metal adsorption on graphene with boron substitution and various vacancy defects are investigated using density functional theory calculation. Hydrogen adsorption characteristics and electronic structure of H2/metal adsorbed graphene were also calculated. It was found that Li, Al, Ca and Ti metal atoms are well dispersed on the graphene and can form a (2 x 2) pattern because clustering of metal atoms is hindered by the repulsive Coulomb interaction between the metal adatoms and the strong bonding force between the dispersed metal atom and graphene. Ca and Ti metal adatom show strong binding energy with the graphene in the cases of B substitution and specific vacancy, respectively. Ca and Ti were also found to be able to 8H2 molecules on the double side of the boron substituted graphene. This allows for a storage capacity of a 8.5 and 7.9 wt% hydrogen for Ca and Ti adatom, respectively.