Nanoconfinement of Molecular Magnesium Borohydride Captured in a Bipyridine-Functionalized Metal–Organic Framework

The lower limit of metal hydride nanoconfinement is demonstrated through the coordination of a molecular hydride species to binding sites inside the pores of a metal–organic framework (MOF). Magnesium borohydride, which has a high hydrogen capacity, is incorporated into the pores of UiO-67bpy (Zr6O4...

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Bibliographic Details
Published in:ACS nano 2020-08, Vol.14 (8), p.10294-10304
Main Authors: Schneemann, Andreas, Wan, Liwen F, Lipton, Andrew S, Liu, Yi-Sheng, Snider, Jonathan L, Baker, Alexander A, Sugar, Joshua D, Spataru, Catalin D, Guo, Jinghua, Autrey, Tom S, Jørgensen, Mathias, Jensen, Torben R, Wood, Brandon C, Allendorf, Mark D, Stavila, Vitalie
Format: Article
Language:English
Subjects:
Anions
coordination chemistry
Hydrogen
hydrogen storage
Materials
metal hydrides
Metal organic frameworks
Metals
metal−organic frameworks
nanoconfinement
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Summary:The lower limit of metal hydride nanoconfinement is demonstrated through the coordination of a molecular hydride species to binding sites inside the pores of a metal–organic framework (MOF). Magnesium borohydride, which has a high hydrogen capacity, is incorporated into the pores of UiO-67bpy (Zr6O4(OH)4(bpydc)6 with bpydc2– = 2,2′-bipyridine-5,5′-dicarboxylate) by solvent impregnation. The MOF retained its long-range order, and transmission electron microscopy and elemental mapping confirmed the retention of the crystal morphology and revealed a homogeneous distribution of the hydride within the MOF host. Notably, the B-, N-, and Mg-edge XAS data confirm the coordination of Mg­(II) to the N atoms of the chelating bipyridine groups. In situ 11B MAS NMR studies helped elucidate the reaction mechanism and revealed that complete hydrogen release from Mg­(BH4)2 occurs as low as 200 °C. Sieverts and thermogravimetric measurements indicate an increase in the rate of hydrogen release, with the onset of hydrogen desorption as low as 120 °C, which is approximately 150 °C lower than that of the bulk material. Furthermore, density functional theory calculations support the improved dehydrogenation properties and confirm the drastically lower activation energy for B–H bond dissociation.
ISSN:1936-0851
1936-086X
DOI:10.1021/acsnano.0c03764