Experimental studies on intermediate compound of LiBH4

Abstract

The formation condition of an intermediate compound of LiBH 4 during the partial dehydriding reaction and its local atomistic structure have been experimentally investigated. LiBH 4 changes into an intermediate compound accompanying the release of approximately 11 mass % of hydrogen at 700-730 K. The Raman spectra indicate that the B-H bending and stretching modes of the compound appear at lower and higher frequencies, respectively, as compared to those of LiBH 4 . These features are consistent with the theoretical calculation on the monoclinic Li 2 B 12 H 12 , consisting of Li + and ͓B 12 H 12 ͔ 2− ions, as a possible intermediate compound of LiBH 4 .

In situ X-ray Raman spectroscopy study of the hydrogen sorption properties of lithium borohydride nanocomposites

“…1) and the assignment in an earlier report. 25 The LiBH 4 -C deh (Fig. 4, brown line) has a band which is slightly broader than for the LiH reference, but at first glance it seems that the Li K-edge XRS spectrum of LiBH 4 -C deh contains all the features of the XRS spectrum of LiH.…”

A thermodynamic assessment of LiBH4

“…In fact, even if traces of Li 2 B 12 H 12 have been detected in the decomposition products according to reaction (15) [28,46,47], the metastable decomposition reaction (17) is also present [44]. The decomposition reaction (16), leading to Li 2 B 10 H 10 , is less favoured than reaction (15), but it is close to reaction (17).…”

“…3), at 1 bar H 2 pressure, Li 2 B 12 H 12 should be stable above 500 K and a driving force for reaction (15) should be present above that temperature. This driving force could explain the hydrogen transport detected in LiBH 4 below the melting temperature [58], as well as the small hydrogen release detected during melting [35,39,46]. In fact, at these temperatures, there should be no driving force for the decomposition into LiH according to reaction (17) pathway, so that release of H 2 should not be observed.…”

“…Price et al [41], on the basis of a study on the decomposition pathways of LiBD 4 -MgD 2 multicomponent systems investigated by in-situ neutron diffraction, calculated an enthalpy and entropy of reaction (4) [28,46] and it has been confirmed experimentally by Raman spectroscopy [46] and NMR [47]. This intermediate com-pound also occurs during dehydrogenation of LiBH 4 nanoconfined in the aerogel [10].…”

“…(11), once again driving the molar heat capacity of the liquid phase toward that of the orthorhombic phase at low temperatures and checking the continuity of the enthalpy, entropy and molar heat capacity of the liquid phase at the melting temperature (551 K). [28,46,47] but parameters for the description of its GFE are not available, a specific assess-ment of thermodynamic properties of this phase has been carried out. This phase has been treated as a stoichiometric phase, so that GFE has been described as Li2 B12 H12 G 2 ¼ 12 B G Rhombo þ6 H2 G Gas þ2 Li G BCC þAþBT ð13Þ…”