New double-cation borohydrides for on-board hydrogen storage Inge Lindemann, Roger Domènech Ferrer,...
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Transcript of New double-cation borohydrides for on-board hydrogen storage Inge Lindemann, Roger Domènech Ferrer,...
New double-cation
borohydrides for
on-board hydrogen storage
Inge Lindemann, Roger Domènech Ferrer, Yaroslav
Filinchuk, Radovan Černý, Hans Hagemann, Ludwig Schultz,
Oliver Gutfleisch
H2 as energy carrier?
• Highly abundant– Electrolysis of water
• Clean– Oxidation product is H2O
• Longterm energy carrier
• High energy density– 120 MJ/kg vs. 44 MJ/kg petrol
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no H2 with H2
Compaction of H2
• Basically 3 different options:
7.6 wt.% H2 1.4 wt.% H2
MgH2
~35 kg/m3
Liquid H2
(23K, opened system)
~70 kg/m3>100 kg/m3
Solid state H2 storage
Density:
Pressurized H2
Schlapbach & Züttel, Nature 414 (2001), 354
4kg H2
For ~400km
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Requirements on the material
1) High gravimetric H2 density > 6 wt.% H2
2) ΔH ~ 20-40 kJ/mol, 60-120°C at 1bar H2 (PEM fuel
cell)
3) Reversibility
4) Good cycle life
5) Fast kinetics
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• Complex hydrides• Light cation for high hydrogen
content (> 6 wt.% H2)
• But either too stable or too unstable
Conventional:LiBH4, Ca(BH4)2, Al(BH4)3,...
• Electronegativity of cation key for borohydride stability
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Borohydrides
+ -
(BH4)-
M+
Y. Nakamori et al., Phys. Rev. B 2006, 74, 045126
NaAl(BH4)4 14.2 wt.% H2
LiAl(BH4)4 17.2 wt.% H2
• Metathesis by high energy ball milling – 1bar Ar (Fritsch P6)– Different molar ratios: 1:2, 1:3, 1:4, 1:5
– Monitoring of p & T
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Synthesis
(2) AlCl3 + 4 NaBH4 NaAl(BH4)4 + 3 LiCl
(1) AlCl3 + 4 LiBH4 LiAl(BH4)4 + 3 LiCl
Hummelshøj et al., J. Chem. Phys. (2009) 131, 014101
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Structure determination• Structure analysis from SR-PXD of 1:5 powder showed
very different structure than expected
• Usually exchange of cations: LiAl(BH4)4
• Primitive cubic unit cell• Complex framework
Al3Li4(BH4)13
Ideal stoichiometry for metathesis:
1:4.33
[Al(BH4)4]-
[Li4(BH4)]3+
Lindemann et al., Chem. Eur. J. 16 (2010), Issue 29,8707–8712.
• Thermogravimetric and desorption analysis- Desorption analysis in static vacuum- Gravimetric analysis in 1bar Ar
Decomposition analysis
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• Weight loss and gas
desorption at ~70°C
• Powder with ideal stochiometry (1:4.33) shows highest weight loss of about 25 %
• desorption of not only H2 but also B2H6
Decomposition Products?
LiBH4 (h)
Al3Li4(BH4)13
LiBH4 (o)
LiBH4 (o)
• Structural analysis by in-situ Raman spectroscopy
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Na-Al-Borohydride
• Structure determination revealed an orthorombic structure- very high Cl content
NaAl(BH4)xCl4-x
1.0<x<1.43
• Only stable with Cl incorporation
• NaSc(BH4)4 exists
• Al3+ might be too small (in comparison to Sc3+)
• Reduced H2 density- theoretical: 14.2 wt.%- experiment: ~3 wt.%
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Conclusion
• Synthesis of two new double-cation systems
1) Al-Li-Borohydride:
• Structure determination – Unique framework structure within the borohydrides Al3Li4(BH4)13
– primitive cubic unit cell containing complex cations and anions!
• Low Tdec at ~70°C
• During decomposition formation of LiBH4 while releasing B2H6 and
H2
2) Na-Al-Borohydride:
• Structure determination– Only stable by Cl incorporation
– Reduces H2 content (only ~3 wt.%)
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Acknowledgement
IFW Dresden
Dept. 21
especially B.Gebel, M.Herrich, C. Rongeat, C.Geipel
University of Geneva
Radovan Černý (Laboratory of Crystallography)
Hans Hagemann (Dept. of Physical Chemistry)
Catholic University of Leuven Yaroslav Filinchuk (Institute of Condensed Matter and
Nanosciences)
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