Ca-Decorated Graphene-Based Three-Dimensional Structures for High-Capacity Hydrogen Storage

Porous three-dimensional (3D) graphene materials decorated with Ca clusters were studied for application to hydrogen storage with the use of the ab initio methods. It was shown that Ca atoms absorb to the sp(3)-bonded vertex sites of the porous materials more strongly than to other planar graphene sites to form chain structures. Hydrogen adsorption on Ca chains at the vertices exhibits the mixed characteristics of mulitpole Coulomb and Kubas interactions depending on the occupation of Ca s or d orbital-derived states. Such H-2 binding characteristics are also investigated for Ca dimers on defective planar graphenes. The storage capacity of the porous 3D structures is estimated to reach about 5-6 wt % at a preset condition of temperatures and pressures.