1. High temperature steam electrolysis (HTSE) for hydrogen production:
from material developement to stack operation
Julie Mougin, G. Gousseau, B. Morel, F. Lefebvre-Joud, F. Le Naour, F. Chauveau, J.C. Grenier CEA-Grenoble, France ICMCB-Bordeaux, France Fourth NEA Information Exchange Meeting on Nuclear Production of Hydrogen Chicago, Oakbrook, 13 – 16 April 2009
"WP6 Green Fuel Cell meeting - Grenoble 19/01/06"

2. HTSE: from material development to stack operation
Outline
Introduction
Experimental
Stack/SRU design
New cell electrode material
Results
Stack performances and short-term durability
SRU performances
New cell electrode performance
Conclusions

3. Instrumented SRU (single repeat unit) Materials and components
Introduction
High temperature steam electrolysis (HTSE) = one of the most promising “clean” processes for massive production of hydrogen
Nuclear energy considered to provide electricity and heat to split water molecule into H2 and O2
Necessity of highly efficient systems in order to avoid too many dedicated nuclear power plants
 each component has to be optimized, from the balance of plant to the stack and to the solid oxide electrolyzer cell (SOEC)
CEA (French Atomic Energy Commission) is carrying out researches in this field:
 To identify and understand
specificities of stack environment
To investigate new solutions
in stack environment
Instrumented SRU (single repeat unit)
 To increase hydrogen
production and durability
Cell materials, coatings
and sealings
Materials and components
Several designs
specific to HTSE
 One low-weight stack
Stack design

4. Experimental: Stack Stack designed at CEA targeting:
Low weight: stamped sheets
High compactness: 2 MW/m3 of power density
Easy assembling
Simple operation
Planar and square cells: 150 x 150 mm², active area 200 cm² Electrolyte supported cell: TZ3Y electrolyte: 90 µm thick Ni-CGO hydrogen electrode LSM oxygen electrode
Interconnects: Inconel600 no coatings up to now
Two short stacks
made of 3 cells tested

5. Experimental: SRU
SRU designed in the framework of the European Project RelHy (coordinated by CEA, FP7)
Design
Robust, easy to instrument
Planar and square cells: 120 x 120 mm², active area 100 cm²
Electrolyte supported cell or electrode supported cell
Electrolyte supported cell: TZ3Y electrolyte: 90 µm thick Ni-CGO hydrogen electrode (La,Sr)(Co,Fe)O3 oxygen electrode (LSCF)
Glass sealings
Crofer22APU with coatings

6. Experimental: cell with new electrode material
New electrode material jointly developed by ICMCB and CEA:
Nickelate Nd2NiO4+δ for oxygen electrode
Mixed electronic and ionic conductivity due to large oxygen overstoichiometry
Screen printed on commercial half electrolyte supported cell
Oxygen electrode
Nd2NiO4+δ 30 µm
TZ3Y electrolyte:
90 µm thick
Hydrogen electrode
Ni-CGO 30 µm
Tested in planar and circular button cell: active area 3.14 cm² (diam. 20 mm) Comparison with the same electrolyte supported cell but containing classical LSM oxygen electrode

7. Experimental: testing procedure
Stack:
T = 820°C
Pure water vapor at the hydrogen electrode
SRU:
T = 800°C
Several ratio of H2O/H2 to the hydrogen electrode
90% H2O / 10% H2
70% H2O / (10% H2 / 20% N2)
50% H2O / (10% H2 / 40% N2)
Cell:
T = °C
Gas to the hydrogen electrode: 35% H2O / 37% H2 / 28% Ar
Stack/SRU/cell Performance:
i-V curve
ASR measured at 1.3 V
Stack durability:
Under galvanostatic control to achieve ~ 1.3 V per cell

8. Results: Stack performances
i-V curves obtained at 820°C in pure water vapor at the hydrogen electrode
ASR (.cm²)
at 1.3 V
Test 1
Test 2
Cell 1
2.45
2.95
Cell 2
2.37
2.24
Cell 3
1.93
2.73
Design validated through two consistent tests
Hydrogen production:
6.7 and 6.6 mg/cm²/h at 1.3V
Corresponding steam utilization:
64% and 52%
For comparison: single cell performance: ASR = 1.4 .cm²
Loss of 0.5 to 1.6 .cm² due to contacting issues in the stack
Next step: coatings and contact layers on interconnects

9. Results: Stack durability
Durability curve at 820°C – galvanostatic control (36 A)
Lowest degradation rate
on central cell
Higher degradation rates
on extreme cells
Event: V increase associated to T increase
Crack in the cell ?
U (t=0)
U (t=406 h)
Degradation
ΔV/1000 h
%/1000 h
Cell 1
1.40
1.67
0.677 49
Cell 2
1.24
1.29
0.123 10
Cell 3
1.33
1.52
0.468 35

10. Results: SRU performance
i-V curves obtained at 800°C in H2O/H2/N2 (several ratio)
ASR50/50
=0.86 .cm²
ASR70/30=0.84 .cm²
ASR90/10=
0.77 .cm²
Cathodic gas composition: secondary effect on the SRU performance

11. Results: SRU performance
i-V curves obtained at 800°C in H2O/H2/N2 (several ratio)
Gas mixture at cathode side
ASR (.cm²)
at 1.3 V
H2 production (mg/cm²/h) at 1.3V
H2 production (mg/cm²/h) at 1.5V
Steam utilization rate (%)
at 1.5 V
50%H2O -10%H2- 40%N2
0.86
18.7
26.2 62 87
70%H2O -10%H2- 20%N2
0.84
19.8
28.0 47 67
90%H2O -10%H2
0.77
20.9
29.9 39 55
Performances improved compared to stack thanks to the use of improved cell and of coatings
Lowest target of the RelHy project achieved: 30 mg/cm²/h

12. Results: cell performance
i-V curves obtained at °C in H2O/H2/Ar
Current density
Cell voltage
Hydrogen production
Nd2NiO4+
LSM
Performance increase thanks to Nd2NiO4+:
1.7, 3 and 4.2 times at 850, 800 and 750°C respectively
 Nd2NiO4+ particularly appropriate for T<800°C T
(°C)
ASR at 1.3 V (.cm2)
H2 production (mg/cm²/h) at 1.3 V
750
0.96
15.0
800
0.58
23.9
850
0.43
32.5
Good H2 production: level better than RelHy SRU due to improved electrode material

13. Results: cell performance
i-V curves obtained at °C in H2O/H2/Ar
Current density
Cell voltage
Hydrogen production
Nd2NiO4+
LSM
Hysteresis effect:
Joule heating effect?
Activation phenomenon?

14. Conclusions
The stack design has been validated through two consistent tests of
3 cells stacks:
ASR ~ 2-3 .cm² at 820°C
H2 production ~ 7 mg/cm²/h at 1.3 V
Degradation rate evaluated for 400 hours:
10% /1000h on central cell
35 and 49% /1000h on extreme cells
SRU:
ASR ~ .cm² at 800°C
H2 production ~ 20 mg/cm²/h at 1.3 V
Cell with new oxygen electrode Nd2NiO4+:
ASR ~ 0.6 .cm² at 800°C
H2 production ~ 24 mg/cm²/h at 1.3 V
Performances 3 times higher than with regular LSM oxygen electrode
Material particularly suitable at T<800°C

15. Perspectives
Stack:
Use of coatings and contact layers to improve performances and durability
Test of 1 kWe stack
SRU:
Durability test
Further improvement of performances
Cell with new oxygen electrode Nd2NiO4+:
Integration into large cells
Test in stack/SRU environment
Durability test

16. Ackowledgments Colleagues:
From CEA: André Cahtroux, Patrick Mayoussier, Patrick Le Gallo, Pierre Baurens
From ICMCB: Jean-Marc Bassat, Fabrice Mauvy
From ECN: Jan-Pieter Ouweltjes
The French research Agency (ANR) and its Hydrogen and Fuel Cells program (Pan-H) for co-financing the SEMI-EHT project
The European Commission for co-financing the RelHy project