Computational Study of hydrogen storage characteristics of the Covalent-Bonded Graphites.

We perform electronic structure calculations to investigate hydrogen-storage characteristics of the solid carbon structures which consist of covalent-bonded graphenes. First, we show that some regular or irregular combinations of \textbf{\textit{sp}}$^{2}$-and \textbf{\textit{sp}}$^{3}$-bonded carbon atoms lead to very stable porous carbon structures, which is designated as the covalent-bonded graphites (CBGs). Using the density-functional calculation and the M{\o}ller-Plesset perturbation method we show that the H$_{2}$ molecular bindings in CBGs are stronger than those on the isolated graphene by about 20{\%}. We also suggest the CBGs with appropriate pore sizes can be utilized as framework structures for dispersing metal atoms. Energetics show that the Ti atoms are likely to be adsorbed at vertex sites of the CBGs. The hydrogen adsorption properties on metal atoms dispersed inside the CBGs are also presented.