Transcript Title goes here

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
World energy consumption
To reduce oil dependency  Hydrogen
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
Contents

Material requirements
– Examples

Non-transition light metal hydrides
 Experimental developments
 Al-Li materials
 Conclusions and further work
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
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
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
Kinetics

1 μm / s
E.g. MgH2
at 600 K
 Slow
diffusion
Hydrogen storage materials
Key properties
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 H2
– Li3AlH6 + 2 Al  3 LiH + 3 Al + 1.5 H2
– 3 LiH + 3 Al  3 AlLi + 1.5 H2

Slow kinetics
 Catalysts, as Fe, Ti and Zr
– Make some steps reversible
– Improve the kinetics
[150-175 oC]
[180-220 oC]
[387-425 oC]
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
Gas analysis techniques

Hydra
–
–
–
–

Hydrogen absorption and desorption experiments
Desorption detection limits 1013 - 1022 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
Hydra
Hydra
Mix volume
Expansion
volume
M1
10-2-10 Pa
M2
10-105 Pa
M0
0.1-6 MPa
Gas inlet
To pumps
Pd filter
Mass analyser
Cell (90-900 K)
Hydra (static)
Mix volume
Expansion
volume
M1
1015-1017 H2
M2
1017-1022 H2
M0
0.1-6 MPa
Gas inlet
To pumps
Pd filter
Mass analyser
Cell (90-900 K)
Hydra (dynamic)
Mix volume
Expansion
volume
M1
M2
M0
0.1-6 MPa
Gas inlet
To pumps
Mass analyser
1012-1015 H2/s
1013-1016 H2
Pd filter
Cell (90-900 K)
Hydra software
LAH01-02.jnb - Calibrated
Desorption of LiAlH4Lithium Aluminium Hydride
Temperature (C)
20
-1 -1
Release rate (10 molec s g )
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

200
4.0
400
Any gas
H2
3.5
1.0
1
0
2
3
0.0
400
600
800
Temperature (K)
Sputter deposited Al-Li: SEM

SEM evidences the formation of columnar structures
in the nm range, size increases with distance from
substrate
Pd
Al Li
~1 µm sputter deposited Pd
layer
~1 µm sputter deposited Al-Li at
room temperature, the layer
contains 5at.%Li (NDP)
Sputter deposited Al-Li: Hydrogen
Around 0.5 at.H%
 Recharging results in
low T peak of 0.3 at.H%
30
-2
-1
H2 cm s )
35
13
– High sensitivity
– Easy background
estimation
– Peaks indicate kinetics
processes

Deposition of AlLi layer (5at%Li)
at 250 K with 50%Ar/50%H2
Pd layer deposited on top
Dynamic
measurements:
Desorption rate (10

Heating rate 0.8 K/s
Released 4x1016 H2
25
20
15
10
5
0
200
300
400
500
600
Temperature (K)
700
800
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
Further information

Contact
– A. Rivera:
– A. van Veen:
[email protected]
[email protected]