On the Mechanism of Hydrogen Storage in a Metal−Organic Framework Material

Abstract

Monte Carlo simulations were performed modeling hydrogen sorption in a recently synthesized metal-organic framework material (MOF) that exhibits large molecular hydrogen uptake capacity. The MOF is remarkable because at 78 K and 1.0 atm it sorbs hydrogen at a density near that of liquid hydrogen (at 20 K and 1.0 atm) when considering H2 density in the pores. Unlike most other MOFs that have been investigated for hydrogen storage, it has a highly ionic framework and many relatively small channels. The simulations demonstrate that it is both of these physical characteristics that lead to relatively strong hydrogen interactions in the MOF and ultimately large hydrogen uptake. Microscopically, hydrogen interacts with the MOF via three principle attractive potential energy contributions: Van der Waals, charge-quadrupole, and induction. Previous simulations of hydrogen storage in MOFs and other materials have not focused on the role of polarization effects, but they are demonstrated here to be the dominant contribution to hydrogen physisorption. Indeed, polarization interactions in the MOF lead to two distinct populations of dipolar hydrogen that are identified from the simulations that should be experimentally discernible using, for example, Raman spectroscopy. Since polarization interactions are significantly enhanced by the presence of a charged framework with narrow pores, MOFs are excellent hydrogen storage candidates.

Molecular simulation of hydrogen diffusion in interpenetrated metal–organic frameworks

“…The whole MD simulations were performed under room temperature, and the Nose´-Hoover chain (NHC) thermostat as formulated by Martyna et al 25 was used to maintain the constant-temperature condition. Similar to previous works, 5,6,[9][10][11][12] all the IRMOFs studied in this work were treated as rigid with atoms frozen at their crystallographic positions during simulations. Although the diffusion properties of guest molecules may depend significantly on the lattice dynamics of MOFs, 12 the interactions between H 2 molecules and the frameworks of MOFs are weak and our purpose is to perform a comparative study on IRMOFs with and without catenation; thus the treatment of rigid MOFs is reasonable.…”

“…3 Apart from substantial experimental studies on the gas adsorption and diffusion in non-interpenetrated MOFs, 4 there are also many theoretical works on them. 5 For example, Frost et al investigated the influencing factors on the hydrogen uptake in IRMOFs by using the grand-canonical Monte Carlo (GCMC) simulation method 6 and Ramsahye et al studied the breathing effect of the MIL-53 and MIL-47 frameworks on CO 2 adsorption; 7 the hydrogen adsorption sites in Zn-MOFs were clarified by both quantum chemical 8 and classical simulation studies. 9 In addition, Skoulidas and Sholl investigated the self-and transport diffusion of several light gases in MOFs in detail using the molecular dynamics method, 10 and framework-flexibility effects on gas adsorption and diffusion in Zn-MOF were investigated by several groups.…”

Wasserstoffspeicherung in mikroporösen metall‐organischen Gerüsten mit koordinativ ungesättigten Metallzentren

“…[52] Die Behandlung solch komplexer Feststoffsysteme wird dadurch erschwert, dass DFT-Rechnungen durch die Berück-sichtigung offenschaliger Konfigurationen und negativer Ladungen numerisch aufwändig und unzuverlässig werden. Die Modellierung der Wechselwirkung von H 2 mit koordinativ ungesättigten Metallzentren in metall-organischen Gerüsten ist somit immer noch eine wichtige und größtenteils ungelöste Aufgabe.…”

Molecular simulations of adsorption of RDX and TATP on IRMOF-1(Be)

“…Since the adsorption of hydrogen in IRMOF-1 has been widely investigated at the DFT level and by using molecular mechanics simulations we will mention at least a few of these studies [22][23][24][25][26][27][28]. Microscopically, hydrogen interacts with the MOF via three principle attractive potential energy contributions: Van der Waals, charge-quadrupole, and induction [23,25].…”

“…Microscopically, hydrogen interacts with the MOF via three principle attractive potential energy contributions: Van der Waals, charge-quadrupole, and induction [23,25]. Metal-oxygen clusters are preferential adsorption sites for hydrogen in MOFs, and the effect of the organic linkers becomes evident with increasing pressure [24].…”