Calcium-decorated graphene for hydrogen storage: A van der Waals density functional study

The hydrogen storage of Ca-decorated graphene is studied by using a recently developed van der Waals density functional [vdW-DF, M. Dion, et al., Phys. Rev. Lett. 92 (2004) 246401]. Our vdW-DF calculations show that Ca-decorated graphene with a coverage of 33.4% can only store 2.6 wt.% of hydrogen. vdW-DF significantly improves the underestimation (overestimation) of binding strength of Ca with graphene as well as the adsorption energies of H2 molecules on Ca-decorated graphene with respect to the conventional local and semilocal approximations.