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

Abstract

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 $\left({\text{H}}_2\right)$ in both high gravimetric $\left(4.6\text{wt}\%\right)$ and high volumetric (36 g/l) capacities. Even higher capacities ($5.7\text{wt}\%$ and 45 g/l) can be obtained in a rationally designed covalent organic framework system, COF-$\alpha$ , with decorated Ca. Both density functional theory and second-order Møller–Plesset perturbation calculations show that the ${\text{H}}_2$ binding in these systems is significantly stronger than the van der Waals interactions, which is required for ${\text{H}}_2$ storage at near ambient conditions.