Metal hydrides with a high hydrogen content are important for materials-based hydrogen storage and for high-temperature superconductivity. Nanoscaling is a well-known strategy to tune the stability and reactivity of various classes of metal hydrides. Confinement of molecular metal hydride species inside the pores of Metal-Organic Frameworks (MOFs) and Covalent-Organic Frameworks (COFs) is of particular interest due to tunability of the pore size and chemical functionality, modularity, and long range order. Recently, our group successfully demonstrated nanoconfinement of aluminum hydride (AlH3) and magnesium borohydride (Mg(BH4)2), anchored to specific sites inside of a bipyridine-functionalized covalent triazine framework (CTF-bipyridine) and a bipyridine-functionalized MOF, UiO-67bpy or (Zr6O4(OH)4(bpydc)6, where bpydc2− is 2,2′-bipyridine-5,5′dicarboxylate. Here, we report confinement of aluminum hydride, lanthanum hydride (LaHx) and calcium borohydride Ca(BH4)2 inside the pores of UiO-67bpy by solvent impregnation. The thermal stability and long-range order of UiO-67bpy after infiltration was confirmed by thermogravimetric analysis (TGA) and powder X-ray diffraction (PXRD). FTIR and Raman spectroscopy was used to identify the main spectral features of the confined species. Further, preliminary transmission electron microscopy (TEM), electron energy loss spectroscopy (EELS) and energy dispersive spectroscopy (EDS) revealed a homogeneous distribution of the hydride within the MOF host. Sieverts measurements were used to quantify the amount of hydride present and to probe the reversibility. Our studies demonstrate that strong interactions between the host and the hydride modify the thermodynamic stability and alter the reaction pathways during hydrogen uptake and release.

Molecular confinement of metal hydrides inside the pores of bipyridine-functionalized metal−organic frameworks

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