LiF-MgB 2 composites are proposed for reversible hydrogen storage. With respect to pure LiBH 4 , a significantly kinetic destabilization regarding hydrogenation and dehydrogenation is accomplished. The reversible hydrogen storage capacity is up to 6.4 wt %. The kinetic properties are improved significantly during cycling. The formations of the hydridofluoride phases (LiBH 4-y F y and LiH 1-x F x ) are observed by in situ synchrotron X-ray diffraction (XRD) and attenuated total reflection Fourier transform infrared spectroscopy (ATR-FTIR). Hydrogenation and dehydrogenation mechanisms are described on the basis of the formation and decomposition of the hydridofluoride phases, respectively.

Light metal borohydrides are considered as promising materials for solid state hydrogen storage. Because of the high hydrogen content of 11.5 wt % and the rather low dehydrogenation enthalpy of 32 kJ mol−1H2, Ca(BH4)2 is considered to be one of the most interesting compounds in this class of materials. In the present work, the effect of selected TM-fluoride (TM = transition metal) additives on the reversible formation of Ca(BH4)2 was investigated by means of thermovolumetric, calorimetric, Fourier transform infrared spectroscopy, and ex situ, and in situ synchrotron radiation powder X-ray diffraction (SR-PXD) measurements. Furthermore, selected desorbed samples were analyzed by 11B{1H} solid state magic angle spinning nuclear magnetic resonance (MAS NMR). Under the conditions used in this study (145 bar H2 pressure and 350 °C), TiF4 and NbF5 were the only additives causing partial reversibility. In these two cases, 11B{1H} MAS NMR analyses detected CaB6 and likely CaB12H12 in the dehydrogenation products. Elemental boron was found in the decomposition products of Ca(BH4)2 samples with VF4, TiF3, and VF3. The results indicate an important role of CaB6 for the reversible formation of Ca(BH4)2.

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Nanoconfined 2LiBH4–MgH2 is prepared by direct melt infiltration of bulk 2LiBH4–MgH2 into an inert nanoporous resorcinol–formaldehyde carbon aerogel scaffold material. Scanning electron microscopy (SEM) micrographs and energy dispersive X-ray spectroscopy (EDS) mapping reveal homogeneous dispersion of Mg (from MgH2) and B (from LiBH4) inside the carbon aerogel scaffold. Moreover, nanoconfinement of LiBH4 in the carbon aerogel scaffold is confirmed by differential scanning calorimetry (DSC). The hydrogen desorption kinetics of the nanoconfined 2LiBH4–MgH2 is significantly improved as compared to bulk 2LiBH4–MgH2. For instance, the nanoconfined 2LiBH4–MgH2 releases 90% of the total hydrogen storage capacity within 90 min, whereas the bulk material releases only 34% (at T = 425 °C and p(H2) = 3.4 bar). A reversible gravimetric hydrogen storage capacity of 10.8 wt % H2, calculated with respect to the metal hydride content, is preserved over four hydrogen release and uptake cycles.