Theoretical investigation of Ti-adsorbed graphene for hydrogen storage using the ab-initio method

Based on first-principles plane wave calculations, it was shown that boron substituted graphene with Ti metal atom adsorption can be used as a high capacity hydrogen storage material. Boron substitution in graphene enhances the Ti metal adsorption energy, which is much larger than that in the case of pure graphene, and than the Ti cohesive energy. The Ti metal atom can be well dispersed on boron-substituted graphene and can form a 2 x 2 pattern because the clustering of the Ti atoms is hindered by the repulsive Coulomb interaction between them. The H2 adsorption behavior on Ti metal atoms was investigated, along with the H2 bonding characteristics and the open-metal states of Ti. It was found that one Ti adatom dispersed on the double sides of graphene can absorb up to eight H2 molecules, corresponding to a 7.9% hydrogen storage capacity. In addition, the adsorption behaviors of non-H2 atoms like C and B were calculated to determine if Ti atoms can remain in an open-metal state in boron-substituted graphene.