Effect of metal doping, boron substitution and functional groups on hydrogen adsorption of MOF-5: A DFT-D study

Abstract

In the present work, adsorption of hydrogen molecules over a metal organic framework (MOF-5) has been investigated by using first principles density functional theory (DFT). Different strategies have been applied for improving hydrogen storage, i.e. metal doping, boron substitution and functionalization. The metal atoms used for enhancing hydrogen adsorption include Li, Ca and Sc. It is found that the binding energy between these metal atoms and MOF is not enough to prevent clustering. Therefore a number of carbon atoms are substituted by boron atoms and it is indicated that boron substitution enhances the binding energies, significantly. Also the results reveal that boron substituted MOF doped by Sc atom has the maximum capacity of hydrogen storage compared to other dopants, with binding energies all in the favorable range of 0.2–0.4eV. On the other hand the effect of functionalization of MOF with halogen atoms is investigated. One and four hydrogen atoms of benzene ring in MOF are replaced by F, Cl and Br atoms. It is found that only MOF functionalized with four Cl and Br atoms improve the hydrogen binding energy. MOF containing four Cl atoms is more promising structure for hydrogen storage in comparison to MOF functionalized with Br atoms because of lower mass of Cl atoms and more favorable hydrogen binding energies.