1. Metal hydride formation and hydrogen storage in Al-Li alloys IRI Symposium May 22, 2003
A. Rivera
Defects in Materials, IRI, TUDelft
Work supported by the Delft Institute for Sustainable Energy (DISE)
Contributors at DM:
A. van Veen (head), F. Labohm, J. de Roode, W.J. Legerstee, K.T. Westerduin, S.W.H. Eijt, H. Schut.
External contributors (Materials Science Faculty, TUDelft):
R. Delhez, N. van der Pers

2. World energy consumption
To reduce oil dependency  Hydrogen

3. How to store hydrogen? A 1000 kg car consumes
5-6 kg fuel/100 km
The same car would consume
2 kg H2/100 km in combustion mode or
1 kg H2 /100 km in fuel cell mode
However, at room temperature and atmospheric pressure 1 kg H2 occupies 11 m3
Storage:
Pressurised vessels
Liquified H2
Sorbed at surface or bulk materials

4. Contents Material requirements Non-transition light metal hydrides
Examples
Non-transition light metal hydrides
Experimental developments
Al-Li materials
Conclusions and further work

5. Material requirements
Storage capacity > 5 wt. %
Fast reaction kinetics
H2 release: 100 kPa at T < 200 ºC
Reversibility in the range 0 – 200 ºC
Resistance to degradation
Cost
Safety

6. Sources of inefficiencies
Hysteresis between absorption and desorption
Hydride stability
Limited kinetics
Poor heat conduction
Small diffusion constant
Surface reactions
Necessity for initial hydriding activation
Sensitivity to air, impurities or other gases
Volume expansion
Decrepitation into fine powder

7. Storage and release Hydrogen in solution: α-phase
Hydrogen in hydride: β-phase
Formation of hydride: α & β
M + ½xH2  MHx + ΔQ
Isotherm flat
More plateaux can appear
Desorption isotherm is lower due to stress
This is undesired for hydrogen storage
Formation enthalpy can be obtained

8. Kinetics
E.g. MgH2 at 600 K
Slow diffusion
1 μm / s

9. Hydrogen storage materials

10. Key properties

11. Non-transition light metal hydrides
LiAlH4, NaAlH4 (in water  irreversible full H2 release)
High capacities (10 and 5 wt.%, respectively)
No reversible due to decomposition
3 LiAlH4  Li3AlH6 + 2 Al + 3 H [ oC]
Li3AlH6 + 2 Al  3 LiH + 3 Al H2 [ oC]
3 LiH + 3 Al  3 AlLi H2 [ oC]
Slow kinetics
Catalysts, as Fe, Ti and Zr
Make some steps reversible
Improve the kinetics

12. Our approach
Objective: to develop nanostructured light weight alloys for hydrogen storage
Choice: Al-Li compounds
Preparation
Sputtering of Al-Li alloy or LiAlH4
Laser ablation of Al-Li alloy or LiAlH4
Cathodic charge, ion implantation gas or plasma exposure + annealing
Characterisation
Volumetric analyses, Permeation, TDS, XRD, NDP, PBA
Occasionally ERDA, SEM, TEM

13. Gas analysis techniques
Hydra
Hydrogen absorption and desorption experiments
Desorption detection limits H2 molecules
Dynamic measurements give direct information on kinetics
Appropriate for thin films
Permeation
of solved molecules or electrochemically introduced atoms
in situ after sputtering will become available soon
Sensitive thermal desorption spectrometry
Detection limit as low as 1011 H2 molecules
Significantly lower for D2

14. Hydra

15. Hydra Expansion volume M1 10-2-10 Pa M2 10-105 Pa M0 0.1-6 MPa
Mix volume
Gas inlet
To pumps
Pd filter
Mass analyser
Cell ( K)

16. Hydra (static) M1 1015-1017 H2 M2 1017-1022 H2 Expansion volume M0
0.1-6 MPa
Mix volume
Gas inlet
To pumps
Pd filter
Mass analyser
Cell ( K)

17. Hydra (dynamic) Expansion volume M1 M2 M0 0.1-6 MPa Mix volume
Gas inlet
To pumps
Pd filter
Mass analyser
H2/s H2
Cell ( K)

18. Hydra software

19. Desorption of LiAlH4 0.4 mg LiAlH4, 0.1 K/s Total H2: 1.5x1022 g-1
Total gas: 3.9x1022 g-1
0: Hydroxide
1: LiAlH4
2: Li3AlH6
3: LiH

20. Sputter deposited Al-Li: SEM
SEM evidences the formation of columnar structures in the nm range, size increases with distance from substrate
~1 µm sputter deposited Pd layer Pd
~1 µm sputter deposited Al-Li at room temperature, the layer contains 5at.%Li (NDP)
Al Li

21. Sputter deposited Al-Li: Hydrogen
Dynamic measurements:
High sensitivity
Easy background estimation
Peaks indicate kinetics processes
Around 0.5 at.H%
Recharging results in low T peak of 0.3 at.H%

22. Conclusions and further work
Effort to fulfil material requirements
Successful H2 detection techniques
Successful creation of samples by
Sputtering
Laser ablation
Currently:
High Li content samples from LiAlH4 targets
Study of samples with high porosity
Fundamental study of Li nanocrystals in c-Al

23. Further information Contact A. Rivera: Rivera@iri.tudelft.nl
A. van Veen: