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Mechanochemistry of the LiBH4–AlCl3 System: Structural Characterization of the Products by Solid-State NMR

Journal Article · · Journal of Physical Chemistry. C
 [1];  [1];  [1];  [2];  [3]
  1. Ames Lab. and Iowa State Univ., Ames, IA (United States)
  2. Ames Lab. and Iowa State Univ., Ames, IA (United States). Department of Materials Science and Engineering
  3. Ames Lab. and Iowa State Univ., Ames, IA (United States). Department of Chemistry
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The double-cation metal borohydride, Li4Al3(BH4)13, mechanochemically produced from a 13:3 mixture of lithium borohydride (LiBH4) and aluminum chloride (AlCl3), has a low hydrogen desorption temperature; however, the material’s decomposition is accompanied by a large emission of toxic diborane (B2H6). In this study, we found that a decrease of the LiBH4:AlCl3 ratio in the starting mixture yields increased amounts of partially chlorinated products that also dehydrogenate at low temperature, but release negligibly small amounts of diborane. Extensive characterization by solid-state NMR spectroscopy (SSNMR) and powder X-ray diffraction (XRD) found that the 11:3 ratio product maintains the Li4Al3(BH4)13-like structure, with additional Cl– anions substituting for [BH4]– compared to the 13:3 mixture. Further decrease of relative LiBH4 concentration in the starting mixture to 9:3 results in a different product composed of tetrahedral [Al(BH4)4]- and [Al(BH4)2Cl2]- complexes, in which two hydrogen atoms of each borohydride group are bridged to aluminum sites. Additionally, SSNMR revealed the covalent character of the Al–H bonds, which is not observed in Li4Al3(BH4)13. In conclusion, these findings suggest that the Al–Cl bonding present in the chlorinated complexes prevents the formation of Al(BH4)3, which is a known intermediate leading to the formation of diborane during thermal dehydrogenation of the nearly chlorine-free Li4Al3(BH4)13.
Research Organization:
Ames Laboratory (AMES), Ames, IA (United States)
Sponsoring Organization:
USDOE Office of Energy Efficiency and Renewable Energy (EERE), Fuel Cell Technologies Office (EE-3F)
Grant/Contract Number:
AC02-07CH11358
OSTI ID:
1427727
Report Number(s):
IS-J--9595
Journal Information:
Journal of Physical Chemistry. C, Journal Name: Journal of Physical Chemistry. C Journal Issue: 4 Vol. 122; ISSN 1932-7447
Publisher:
American Chemical SocietyCopyright Statement
Country of Publication:
United States
Language:
English

Figures / Tables (8)

Table 1(p. 7)table Table 1
Figure 1(p. 8)figure Figure 1
Figure 2(p. 9)figure Figure 2
Figure 3(p. 11)figure Figure 3
Table 2(p. 11)table Table 2
Figure 4(p. 13)figure Figure 4
Figure 5(p. 15)figure Figure 5
Figure 6(p. 16)figure Figure 6

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Related Subjects

36 MATERIALS SCIENCE
37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY