Ab initio design of Ca-decorated organic frameworks for high capacity molecular hydrogen storage with enhanced binding

Ab initio calculations show that Ca can decorate organic linkers of metal-organic framework, MOF-5, with a binding energy of 1.25 eV. The Ca-decorated MOF-5 can store molecular hydrogen (H2) in both high gravimetric (4.6 wt %) and high volumetric (36 g/l) capacities. Even higher capacities (5.7 wt % and 45 g/l) can be obtained in a rationally designed covalent organic framework system, COF-α, with decorated Ca. Both density functional theory and second-order Møller–Plesset perturbation calculations show that the H2 binding in these systems is significantly stronger than the van der Waals interactions, which is required for H2 storage at near ambient conditions.