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

Abstract

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-freemore » Li4Al3(BH4)13.« less

Authors:
 [1];  [1];  [1];  [2]; ORCiD logo [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
Publication Date:
Research Org.:
Ames Laboratory (AMES), Ames, IA (United States)
Sponsoring Org.:
USDOE Office of Energy Efficiency and Renewable Energy (EERE), Fuel Cell Technologies Office (EE-3F)
OSTI Identifier:
1427727
Report Number(s):
IS-J-9595
Journal ID: ISSN 1932-7447; TRN: US1802735
Grant/Contract Number:  
EE0007047; AC02-07CH11358
Resource Type:
Accepted Manuscript
Journal Name:
Journal of Physical Chemistry. C
Additional Journal Information:
Journal Volume: 122; Journal Issue: 4; Journal ID: ISSN 1932-7447
Publisher:
American Chemical Society
Country of Publication:
United States
Language:
English
Subject:
37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY; 36 MATERIALS SCIENCE

Citation Formats

Kobayashi, T., Dolotko, O., Gupta, S., Pecharsky, V. K., and Pruski, M. Mechanochemistry of the LiBH4–AlCl3 System: Structural Characterization of the Products by Solid-State NMR. United States: N. p., 2017. Web. doi:10.1021/acs.jpcc.7b10856.
Kobayashi, T., Dolotko, O., Gupta, S., Pecharsky, V. K., & Pruski, M. Mechanochemistry of the LiBH4–AlCl3 System: Structural Characterization of the Products by Solid-State NMR. United States. doi:10.1021/acs.jpcc.7b10856.
Kobayashi, T., Dolotko, O., Gupta, S., Pecharsky, V. K., and Pruski, M. Tue . "Mechanochemistry of the LiBH4–AlCl3 System: Structural Characterization of the Products by Solid-State NMR". United States. doi:10.1021/acs.jpcc.7b10856. https://www.osti.gov/servlets/purl/1427727.
@article{osti_1427727,
title = {Mechanochemistry of the LiBH4–AlCl3 System: Structural Characterization of the Products by Solid-State NMR},
author = {Kobayashi, T. and Dolotko, O. and Gupta, S. and Pecharsky, V. K. and Pruski, M.},
abstractNote = {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.},
doi = {10.1021/acs.jpcc.7b10856},
journal = {Journal of Physical Chemistry. C},
number = 4,
volume = 122,
place = {United States},
year = {2017},
month = {12}
}

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Figures / Tables:

Table 1 Table 1: Hydrogen desorption characterization and RGA analysis of decomposition products of LiBH4AlCl3 mixtures of different molar ratios, ball milled for 3 hours.

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Figures/Tables have been extracted from DOE-funded journal article accepted manuscripts.