Enhancement of hydrogen storage properties of metal-organic framework-5 by substitution (Zn, Cd and Mg) and decoration (Li, Be and Na)

Two strategies of decoration by three elements Z = Li, Be and Na in cyclic site, and substitution of Zn by Mg and Cd in unit cell were used in the framework of functional density theory to tune the hydrogen storage properties of metal-organic framework-5 (MOF-5) based on Zn whose decomposition temperature and initial gravimetric capacity are 300 K and 1.57 wt% respectively. Based on the adsorption of hydrogen molecules in the crystal surface at three different adsorption sites with three orientations of H2, we show that our system may reach a maximum gravimetric storage capacity of 4.09 wt% for multiple hydrogen molecules. Moreover, the functionalization of Z combined to the substitution, shows an exceptional improvement of hydrogen storage properties. For example, Mg-MOF-5 decorated with Li2 has a capacity up to 5.41 wt% and 513 K as desorption temperature.