1. Optimization of AB2 - type alloy composition with superior
hydrogen storage properties for stationary applications
Kandavel Manickam, David Grant and Gavin Walker
Energy and Sustainability Research Division
Faculty of Engineering
The University of Nottingham
ICAER 2013, IIT Bombay

2. Outline
1. Introduction
2. Results of AB2 type alloys
•
•
•
•
•
Materials preparation and characterization
P-C-I measurements
Thermodynamics
Hydrogenation kinetics
HP-DSC studies of alloys
3. Summary of results and conclusions

3. Introduction
Year
Limited reserves
CO2
Global warming
Alternative clean energies
Hydrogen can be a clean energy carrier
• High energy density (three time higher than the fossil fuels)
• Environmental friendliness (H2O)
Hydrogen economy
• Production
• Storage
• Utilization

4. BioCPV
• Indo – UK BURD (Bridging the Urban and Rural Divide) Project
• Integration of different types of energy sources and energy storage technologies
12 kWh
16 kWh
14 kWh
H store
End user
Electrolyser
7.5 kWh
2520 litres
CPV- 15 kWp
120 kWh per day
Hydrogen
7 kWh
2350 litres
Bio waste
22 kWh
14000 litres
Bio gas plant (14 m3)
Genset
Village electrification
90 kWh

5. Materials selection requirements
Hydrogen storage
• 7.5 kWh(H2) : 225 g H2
• equivalent to 2520 litres (stp)
• Solid State Storage
• 15 kg AB alloy (1.6 wt %)
• 13 kg of AB2 alloy (1.8 wt %)
Commercial Hydralloy C - AB2 alloy
• Plateau Pressure : 13 bar
• Capacity : 1.3 wt %
Aim of the present work
Requirements
1 g H2/min
Kinetics
• AB2 type Laves phase alloys
• Composition variation to improve
hydrogen storage properties
• Effect of non-stoichiometry on the
hydrogen storage properties
• Identification of suitable composition
for the BioCPV application

6. Synthesis & Characterization
172.0
A1+xB2(x = 0, 0.05, 0.075 and 0.1)
40
50
60
70
3
Unitcell volume (Å )
30
A1+xB2
171.5
x = 0.1
x = 0.075
171.0
170.5
170.0
169.5
Intensity (arb. units)
169.0
0.00
0.04
0.08
0.12
x in A1+xB2
x=0
x = 0.05
x = 0.075
x = 0.1
30
40
(201)
50
2
60
• Single phase formation
• Hexagonal structure (C14)
• space group P63/mmc
(205)
(302)
(104)
(213)
x=0
(202)
(004)
(112)
(200)
(103)
(110)
x = 0.05
70
Composition is similar to initial composition (± 1%)

7. Hydrogen storage
Pressure – Composition Isotherms
Equilibirum Pressure (bar)
100
α phase
2.1 wt %
A1.05B2
10
β
α+β
1
Plateau pressure
o
32 C
o
50 C
o
60 C
o
70 C
0.1
α
0.01
0.0
0.4
0.8
1.2
1.6
Hydrogen concentration (wt %)
α+β phase
2.0
β phase

8. Pressure – Composition Isotherms
A1.05B2
100
100
Equilibirum Pressure (bar)
Hydrogenation
Dehydrogenation
15 bar
10
10
1
1
0.01
0.0
1.55 wt %
o
32 C
o
50 C
o
60 C
o
70 C
0.1
0.4
0.8
1.2
1.6
1 bar
o
32 C
o
50 C
o
60 C
o
70 C
2.0 0.0
0.4
0.8
1.2
1.6
Hydrogen concentration (wt %)
Working capacity (1 to 15 bar) at 32 oC ~ 1.55 wt %
2.0
0.1
0.01

9. 100
A1+xB2
Increase in storage capacity
• Modification of chemical
environment of interstitial
sites
• Size of the interstitial sites
10
1
o
T = 32 C
0.4
0.8
1.2
1.6
Hydrogen Concentration (wt %)
2.0
0.00
2.4
2.0
0.05
0.10
Storage capacity
Working capacity
Plateau pressure
20
Plateau pressure (bar)
x=0
x = 0.05
x = 0.075
x = 0.1
0.1
0.01
0.0
Rietveld analysis and neutron
diffraction
Hydrogen concentartion (wt %)
Equilibrium Pressure (bar)
Pressure – Composition Isotherms
16
1.6
12
1.2
8
0.8
4
0.4
0.00
0.05
x in A1+xB2
0.10
0

10. Thermodynamics
van’t Hoff relation :
𝑙𝑛𝑃 𝐻2 =
Hydrogenation
∆𝐻
∆𝑆
−
𝑅𝑇
𝑅
Dehydrogenation
2.4
2.4
ln PH2
ln PH2
1.6
1.6
0.8
0.8
0.0028
x = 0.05
x = 0.075
x = 0.1
x = 0.05
x = 0.075
x = 0.1
0.0030
0.0032
Hydrogenation
ΔH = - 25 to -28 kJ/mol H2
ΔS = - 92 to -100 J/K/mol H2
0.0028
0.0034
0.0030
0.0032
0.0
0.0034
1/T (1/K)
Dehydrogenation
ΔH = 28 to 32 kJ/mol H2
ΔS = 94 to 112 J/K/mol H2

11. Hydrogenation Kinetics
Avrami-Erofeev rate eq: F = 1- exp(-ktn); n = 0.54 to 3
2.0
6
First order rate equation : - ln(1-F) = kt
5
4
1.5
- ln (1-F)
Hydrogen Concentration (wt %)
Working Capacity
o
A1.05B2
1.0
0
0.0
32 C
o
50 C
o
60 C
o
70 C
20
60
40
80
3
2
100
0
A1.05B2
0
20
60
Time (min)
80
100
β phase
ln D vs 1/T
-29.4
-0.7
-1.4
Ea : 24 ± 1 kJ/mol
0.0030
0.0032
1/T (1/K)
0.0034
2
π 𝐷
𝑟2
r = 5 μm
Arrhenius relation
D = D0 exp(-Ea/kbT)
ln D
ln k
kd=
0.0028
40
Arrhenius relation
k = k0 exp(-Ea/kbT)
lnk vs 1/T
o
32 C
o
50 C
o
60 C
o
70 C
α+β
1
Time (min)
α+β phase
β
-30.0
-30.6
0.0028
Ea : 29 ± 1 kJ/mol
0.0030
0.0032
1/T (1/K)
0.0034

12. Hydrogen gas
Heating rate = 5 oC/min
Flow rate = 100 ml/min
van’t Hoff relation : 𝑙𝑛𝑃 𝐻2 =
∆𝐻
∆𝑆
−
𝑅𝑇
𝑅
Validation of PCI measurements
0.2
20 bar
16 bar
12 bar
8 bar
A1.05B2
0.1
2.8
Dehydrogenation
ln PH2
DSC Heat flow (mW/mg)
High Pressure DSC
0.0
2.1
Hydrogenation
-0.1
1.4
50
100
150
200
250
Hydrogenation
Dehydrogenation
A1.05B2
0.0026
o
0.0028
0.0030
1/T (1/K)
Temperature ( C)
A2B2 Interstitial sites: 24l, 12k, 6h1, 6h2
Low temperature peak : 24l and 6h1
High temperature peak : 12k and 6h2
Hydrogenation
ΔH = - 29 ± 2 kJ/mol H2
ΔS = - 100 ± 4 J/K/mol H2
Dehydrogenation
ΔH = 32 ± 4 kJ/mol H2
ΔS = 117 ± 9 J/K/mol H2

13. Summary of results
PCI measurements
DSC measurements
Plateau slope
factor
ln(P2/P1)
ΔH
ΔS
ΔH
ΔS
(kJ/mol H2)
(J/K/mol H2)
(kJ/mol H2)
(J/K/mol H2)
Alloy 1 (x = 0)
2.7
-
-
- 29 ± 2
- 100 ± 5
Alloy 2 (x = 0.05)
2.4
- 26 ± 2
- 98 ± 5
- 29 ± 2
- 100 ± 4
Alloy 3 (x = 0.075)
2.2
- 25 ± 1
- 92 ± 3
-26 ± 3
- 96 ± 8
Alloy 4 (x = 0.1)
1.9
- 28 ± 1
- 100 ± 2
- 28 ± 1
- 99 ± 1
Alloy

14. Summary of results
Alloy
Plateau
pressure
(bar)
Storage
capacity
at 15 bar
Residual
storage
capacity
(1 bar)
Working
capacity
(15 to 1
bar)
Charge
time : 95
%
(min)
1.7
32 oC 50 oC
Max.
Storage
capacity
(wt%)
@ ~ 35 bar
1.6
0.3
1.3
6
Alloy 1 (x = 0)
6.0
3.2
Alloy 2 (x = 0.05)
5.3
2.8
8.2
5.6
2.1
1.85
0.3
1.55
5
Alloy 3 (x = 0.075)
3.0
1.7
5.4
3.5
2.1
2.0
0.55
1.45
5
Alloy 4 (x = 0.1)
2.2
1.4
4.1
2.4
2.2
2.1
0.7
1.4
5

15. Conclusions
Single phase non-stoichiometric AB2 Laves phase alloys have
synthesized successfully
Alloy 2 (x = 0.05) is most promising for the BioCPV application
Working capacity reached within 5 min at 32 °C
16 % increase in
storage capacity
than Hydralloy C
Interstitial sites can be
modified by preparing
non stoichiometric
alloys

16. Thank you
Manickam.Kandavel@nottingham.ac.uk
David.Grant@nottingham.ac.uk
Gavin.Walker@nottingham.ac.uk
Acknowledgement
- Research group members