Transcript Hydrogen Storage in LiBH4-MgH2-Al

Understanding Li2B12H12
Bjarne R. S.
a Interdisciplinary
a
Hansen
and Torben R.
a
Jensen
Nano Science Center, Center for Materials Crystallography and Department of Chemistry,
University of Aarhus, Langelandsgade 140, DK-8000 Aarhus C, Denmark
Introduction
Light metal borohydrides, such as LiBH4, has a massive potential as hydrogen storage materials for
storage applications in a wide scale. Most borohydrides require high temperatures for hydrogen
release, but this can in many cases be lowered by utilizing eutectic composites, reactive hydride
composites or by nanoconfinement. However, one major challenge still remains: Reversibility!
In practically all metalborohydrides M-B12H12 species are
formed during decomposition which ultimately reduces
[1]
the reversible hydrogen storage capacity . In order to
understand or avoid this more knowledge of these
compounds is required. Therefore this current study
investigates Li2B12H12.
[1]
Sample preparation
In situ SR-PXD
Li2B12H12 - 4 H2O (Katchem) was heated to 240 °C
under dynamic vacuum for 10 h to completely
dry the sample and
obtain an
anhydrous,
[2]
crystalline phase
An in situ SR-PXD experiment on Li2B12H12 was
performed at Maxlab, I711.
At T = 280 °C a phase transformation is observed, and at T = 355 °C the sample turns amorphous and a broad hump is observed.
RT → 700 °C (5K/min), p(H2) = vac.
λ = 0.9941 Å
Li2B12H12
The B12H122- ion [3]
Thermal analysis
β-Li2B12H12
γ-Li2B12H12-x
DSC and TGA indicate three reaction steps are
present, where the first step may be owing to
water contamination. These steps will be fur11
ther investigated using FT-IR and B MAS NMR.
As the temperature increases the hump is shifting
towards lower 2θ angle. The end product is expected to be amorphous B. These observations
agree well with thermal analysis and a previous
[4]
study . The fact that the sample becomes amorphous during heating complicates characterization of the decomposition reactions with PXRD.
11
Therefore B MAS NMR studies are currently
being conducted.
Acknowledgements and references
Sincere acknowledgements are directed to the Interdisciplinary Nano Science Center (iNANO), Danscatt, MAX-Lab
Bor4Store (EU) and Center for Materials Crystallography (CMC)
[1] B. R. S. Hansen et al., J. Phys. Chem. C 2013, 117, 7423−7432 [2] Pitt et al, J. Am. Chem. Soc. 2013, 135, 6930−6941
[3] Whang et al., J. Phys. Chem. C, 2008, 112 (9), 3164–3169 [4] Paskevicious et al, Phys. Chem. Chem. Phys. 2013, 15, 15825