LiBH₄−Mg(BH₄)₂: A Physical Mixture of Metal Borohydrides as Hydrogen Storage Material

The LiBH4−Mg(BH4)2 system has been investigated as a possible hydrogen storage material. Several composites were synthesized by ball milling, namely, xLiBH4−(1−x)Mg(BH4)2 with x = 0, 0.10, 0.25, 0.33, 0.40, 0.50, 0.60, 0.66, 0.75, 0.80, 0.90, 1. The physical mixture was investigated by using X- ray powder diffraction and thermal analysis. Interestingly, already a small amount of LiBH4 makes the α to β transition of Mg(BH4)2 reversible, which has not been reported before. The eutectic composition was found to exist at 0.50 x x = 0.50 composite releases about 7.0 wt % of hydrogen

Nanoconfined LiBH₄ and Enhanced Mobility of Li⁺and BH₄^– Studied by Solid-State NMR

The structural and dynamical properties of LiBH₄ confined in porous carbon and ordered porous silica are studied using ¹H, ⁷Li, and ¹¹B solid-state NMR. The ¹¹B and ⁷Li NMR resonances of LiBH₄ confined in porous carbon (broad pore size distribution up to <60 nm) are strongly broadened compared to bulk LiBH₄. This line broadening is dominated by anisotropic susceptibility effects induced by the nanostructured carbon host. Because of the lack of resolution caused by the anisotropic susceptibility broadening, we studied confined LiBH₄ in ordered porous silica (MCM-41 pore size: 1.9 nm). In the ⁷Li and ¹¹B spectra, a bulk-like LiBH₄ resonance is observed together with an additional, more narrow component. Above <i>T</i> = 313 K, this component showed a typical <i>J</i>-coupling pattern in both ¹¹B and ¹H spectra corresponding to highly mobile BH₄^– species. Static ¹¹B solid-state NMR measurements compared with second moment calculations show that these BH₄^– species not only rotate as in the bulk material but also experience translations through the crystal lattice. Static ⁷Li measurements show that Li⁺ is also highly mobile. Therefore, we conclude that nanoconfinement of LiBH₄ strongly enhances diffusional mobility of borohydride anions and lithium in this material