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New double-cation borohydrides for on-board hydrogen storage

New double-cation borohydrides for on-board hydrogen storage. Inge Lindemann , Roger Domènech Ferrer, Yaroslav Filinchuk, Radovan Černý, Hans Hagemann, Ludwig Schultz, Oliver Gutfleisch. H 2 as energy carrier?. no H 2 with H 2. Highly abundant Electrolysis of water Clean

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New double-cation borohydrides for on-board hydrogen storage

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  1. New double-cation borohydrides for on-board hydrogen storage Inge Lindemann, Roger Domènech Ferrer, Yaroslav Filinchuk, Radovan Černý, Hans Hagemann, Ludwig Schultz, Oliver Gutfleisch

  2. H2 as energy carrier? no H2 with H2 • Highly abundant • Electrolysis of water • Clean • Oxidation product is H2O • Longterm energy carrier • High energy density • 120 MJ/kg vs. 44 MJ/kg petrol 2

  3. Compaction of H2 Solid state H2 storage Pressurized H2 Liquid H2 (23K, opened system) >100 kg/m3 Density: ~70 kg/m3 ~35 kg/m3 MgH2 7.6 wt.% H2 1.4 wt.% H2 • Basically 3 different options: 4kg H2 For ~400km 3 Schlapbach & Züttel, Nature 414 (2001), 354

  4. Requirements on the material • High gravimetric H2 density > 6 wt.% H2 • ΔH ~ 20-40 kJ/mol, 60-120°C at 1bar H2 (PEM fuel cell) • Reversibility • Good cycle life • Fast kinetics 4

  5. 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 Borohydrides M+ (BH4)- NaAl(BH4)4 14.2 wt.% H2 LiAl(BH4)4 17.2 wt.% H2 + - Y. Nakamori et al., Phys. Rev. B 2006, 74, 045126

  6. 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 Synthesis (1) AlCl3 + 4 LiBH4 LiAl(BH4)4 + 3 LiCl (2) AlCl3 + 4 NaBH4 NaAl(BH4)4 + 3 LiCl Hummelshøj et al., J. Chem. Phys. (2009)131, 014101

  7. Al-Li-Borohydride • X-ray diffraction analysis after the milling process

  8. Structure determination [Al(BH4)4]- [Li4(BH4)]3+ • 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 • Lindemann et al., Chem. Eur. J. 16 (2010), Issue 29,8707–8712.

  9. Decomposition analysis • Thermogravimetric and desorption analysis • Desorption analysis in static vacuum • Gravimetric analysis in 1bar Ar • 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 9

  10. Decomposition Products? LiBH4 (o) LiBH4 (h) LiBH4 (o) Al3Li4(BH4)13 • Structural analysis by in-situ Raman spectroscopy 10

  11. 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.% 11

  12. 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 whilereleasing B2H6 and H2 2) Na-Al-Borohydride: Structure determination Only stable by Cl incorporation Reduces H2 content (only ~3 wt.%) 12

  13. 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) 13

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