Understanding Hydrogen Adsorption in Metal−Organic Frameworks with Open Metal\nSites:  A Computational Study

Abstract

Recent experimental investigations show that the open metal sites may have a favorable impact on the hydrogen\nadsorption capacity of metal−organic frameworks (MOFs); however, no definite evidence has been obtained\nto date and little is known on the interactions between hydrogen and the pore walls of this kind of MOFs. In\nthis work, a combined grand canonical Monte Carlo simulation and density functional theory calculation is\nperformed on the adsorption of hydrogen in MOF-505, a recently synthesized MOF with open metal sites, to\nprovide insight into molecular-level details of the underlying mechanisms. This work shows that metal−oxygen clusters are preferential adsorption sites for hydrogen, and the strongest adsorption of hydrogen is\nfound in the directions of coordinatively unsaturated open metal sites, providing evidence that the open metal\nsites have a favorable impact on the hydrogen sorption capacity of MOFs. The storage capacity of hydrogen\nof MOF-505 at room temperature and moderate pressures is predicted to be low, in agreement with the outcome\nfor hydrogen physisorption in other porous materials.