The document summarizes research on high-temperature electrolysis (HTE) conducted at the Idaho National Laboratory (INL). It discusses INL's role in HTE research and development under the DOE initiative. Key areas covered include experimental work, modeling, demonstration projects, and a workshop on degradation mechanisms. Experimental results showed good initial performance but degradation over time. The workshop discussed various degradation mechanisms observed and potential mitigation strategies. INL's ongoing work focuses on developing improved cell compositions and demonstrating long-term stable performance.

1. The High-Temperature Electrolysis
Program at INL: Observations on
Performance Degradation and Summary
of INL-Sponsored Degradation Workshop
J. E. O’Brien
C. M. Stoots, J. S. Herring, K. G. Condie, G. K. Housley,
M. G. McKellar, M. S. Sohal, J. J. Hartvigsen
RelHy Workshop on High Temperature Water
Electrolysis Limiting Factors
June 9 – 10, 2009

2. High-Temperature Electrolysis
INL has been designated as the lead laboratory for High-Temperature
Electrolysis (HTE) research and development, under the DOE Nuclear
Hydrogen Initiative (NHI)

3. INL HTE Research Scope
Experimental
CFD Simulation
Demonstration
and Scale-Up
System Modeling

4. System Modeling
Process flow diagram for the helium-cooled reactor / direct
Brayton / HTE system with air sweep (reference case).

5. System Analysis Results
Overall Hydrogen Production Efficiencies, HTE
Reference Case, as a function of Cell Voltage
0.54
air swp, adiabatic, ASR 0.25
overall hydrogen production efficiency (LHV)
LHV
ηH = air swp, adiabatic, ASR 1.25
2 FVop (1 / ηth − 1) + HHV air swp, isothermal, ASR 0.25
0.52 air swp, isothermal, ASR 1.25
no swp, adiabatic, ASR 0.25
no swp, adiabatic, ASR 1.25
no swp, isothermal, ASR 0.25
0.5
no swp, isothermal, ASR 1.25
simple thermo analysis
0.48
0.46
0.44
1 1.05 1.1 1.15 1.2 1.25 1.3 1.35 1.4
per-cell operating voltage
The red line follows from the definition of the overall thermal-to-hydrogen
efficiency η = LHV and direct application of the first law
∑ Qi
H
i

6. System Analysis Results
Overall Hydrogen Production Efficiencies
HTE Reference Case (air sweep)
vs Hydrogen Production Rate vs Steam Utilization
3 0.5
hydrogen production rate, m /hr
overall hydrogen production efficiency
0 20,000 40,000 60,000 80,000 100,000
0.51
0.45
overall hydrogen production efficiency
0.5 adiabatic, ASR 1.25
isothermal, ASR 1.25 adiabatic, ASR 0.25
adiabatic, ASR 0.25 0.4 adiabatic, ASR 1.25
0.49 isothermal, ASR 0.25 isothermal, ASR 0.25
isothermal, ASR 1.25
0.48 0.35
0.47
0.3
0.46
0.25
0.45 Note: the high-ASR cases shown here
require ~ four times as many cells.
0.44 0.2
0 20 40 60 80 100
0 0.5 1 1.5 2 2.5
hydrogen production rate, kg/s Steam Utilization
fixed utilization (imax corresponds to Vtn)

7. System Analysis Results
Overall Hydrogen Production Efficiencies
Dependence on Reactor Type and Outlet Temperature
60
Overall thermal to hydrogen efficiency (%)
50
40
30
65% of max possible
INL, HTE / He Recup Brayton
20 INL, LTE / He Recup Brayton
INL, HTE / Na-cooled Rankine
INL, LTE / Na-cooled Rankine
INL, HTE / Sprcrt CO2
10 INL, LTE / Sprcrt CO2
SI Process (GA)
MIT - GT-MHR/HTE
MIT AGR -SCO2/HTE
0
300 400 500 600 700 800 900 1000
T (°C)

8. HTE Experimental Program
INL High-temperature electrolysis laboratory
Integrated Laboratory Scale
Small-scale experiments
Facility (15 kW)

9. HTE Experimental Program
Schematic of single-cell electrolysis test apparatus

10. HTE Experimental Program
Exploded view of Ceramatec electrolysis stack components

11. HTE Experimental Program
Cell Performance Characterization: Polarization curves
Button cell stack
-1.6 0.2 1.5
Q = 140 sccm
s, Ar 10-3 10-5
theoretical open-cell potentials
Q = 40.1 sccm
s, H2 25-2
1.4
0 10-4
cell potential power density 25-1
per-cell operating voltage, V
-1.4 -0.1 10-2
1.3
cell power density, p (W/cm )
sweep Tfrn(C) Tdp,i(C)
10-1
cell potential, E (V)
1 800 25.4
2 850 25.6 1.2
3 800 34.3
-1.2 4 850 34.4 -0.4
5 800 47.2 1.1
6 850 47.9 sweep # sccm N2 sccm H2 Tdp, i (C) Tf (C)
10-1 1011 205 48.5 800
1 10-2 2017 411 70.4 800
2
-1 E1 p1
-0.7 10-3 1017 410 83.8 800
E2 p2
10-4 2018 411 82.9 800
E3 p3
E4 p4 0.9 10-5 2018 411 83.2 830
E5 p5 25-1 2013 513 83.8 800
E6 p6
25-2 2013 513 83.4 830
electrolysis mode fuel cell mode
0.8
-0.8 -1 0 0.05 0.1 0.15 0.2 0.25 0.3 0.35
-0.6 -0.4 -0.2 0 0.2 2
2
current density, i ( A/cm ) current density, i (A/cm )
20
Inlet CO
2
H
Outlet gas composition as a function 15 Inlet H
2
2
Mole % (Dry Basis)
of current density for co-electrolysis
CO
experiments, 10-cell stack 10
5 CO
2
Inlet CO
0
0 2 4 6 8 10 12 14
Electrolysis Current (A)

12. HTE Experimental Program
Cell and Stack Performance Degradation
Area-specific resistance vs time over ~ 1000 hrs
2.4
1.4
1.2 2
2
ASR, Ohm cm
1
ASR 1.6
0.8
increased furnace temperature from 800 C to 830 C
1.2
0.6
OCV check
0.4
0.8
0.2
0 200 400 600 800 1000 1200 0 200 400 600 800 1000
elapsed time, hr elapsed time, hrs
Single button cell Stack

13. ANL Post-Test Examination of Ceramatec Cells
(D.Carter, J. Mawdsley)
Electrolyte
O2 Electrode
Chromium deposition in SOEC and
SEM view of the electrolyte and SOFC modes (more uniformly
oxygen electrode showing dispersed in SOEC mode)
delamination and cracks

14. ANL Post-Test Examination of Ceramatec Cells
(D.Carter, J. Mawdsley)
Silica capping layer on H2-electrode
Si is carried by steam from the Si-bearing seal; can also originate from
interconnect plate

15. HTE Experimental Program
Demonstration and Scale-Up: Integrated Laboratory Scale Facility
Exploded view of heat exchanger,
base manifold unit, and four-stack
electrolysis unit ILS modules, mounted in hot zone

16. HTE Experimental Program
Integrated Laboratory Scale Facility
ILS hydrogen production rate time history
Initial production rate in
excess of 5 m3/hr, followed
by serious degradation,
some of which was related
to BoP issues

17. Ceramatec Post-Test Examination of ILS Cells
Cell and interconnect surfaces from the oxygen
electrode side of ILS Cell, showing delamination electrolyte
Oxygen electrode

18. HTE Experimental Program
Performance Improvement: Single-cell test stand (electrode-supported cells)
Exploded view Assembly view Photo

19. INL SOEC Degradation Workshop
• INL organized a workshop titled “Degradation in Solid Oxide
Electrolysis Cells and Strategies for its Mitigation,” during the
2008 Fuel Cell Seminar & Exposition in Phoenix, AZ on
October 27, 2008.
• The workshop was attended by researchers from academia,
national laboratories, industry, several DOE representatives,
and a few researchers from Japan and Germany.

20. Summary of INL Workshop Discussion on SOEC
Degradation Mechanisms
Electrodes
- oxygen electrode delamination
- associated with oxygen evolution in SOEC mode
- possible buildup of high pressures in closed porosity Redox cycling
(can lead to electrode instability)
- morphology change (coarsening), reducing effective surface area of
tpb region
- deactivation due to contaminant transport and deposition
- chromia and silicate transport and cathode poisoning
(enhanced in high-steam environment)
Electrolytes
- Phase change in electrolyte materials with aging
- Electrolytes must be fully stabilized (mechanical strength)
Interconnects and seals
- corrosion and non-conducting scale formation (chromia, alumina,
silica), spallation in metallic interconnects, reaction with sealing
glasses
- Leakage from edge seals or cracked cells => hot spots

21. Mitigation Strategies
1. protective coatings (e.g., Co, Mn spinels) and surface treatments on
interconnects – provides a barrier to inward oxygen and outward Cr
diffusion
2. rare-earth surface treatments on interconnects – promote development
of a stable conductive oxide scale
3. fabrication techniques, materials, operating conditions (e.g., flow
distributions, current density, utilization, steam content,…)
4. cell design, fabrication, materials
5. Use fully stabilized mixture, add ceria or alumina
6. Improved seals, CTE match, all-ceramic cells and stacks

22. Selected Additional Comments from INL Workshop
Minh (GE)
Oxygen Electrodes
• Performance: LSCF > LSF > LSM/YSZ
• Performance stability: LSCF and LSF have shown better performance
stability than LSM/YSZ
• Degradation of LSCF electrode - similar in fuel cell, electrolysis, and
cyclic modes, perhaps enhanced degradation in electrolysis mode
• Mixed conducting oxygen electrodes – better performance and stability
SOEC Stacks
• Degradation rate 0.2-0.3 ohm-cm2/1000 h
• Delamination and elemental migration observed at oxygen electrode
interfaces
• Causes for observed degradation unclear - need to be identified

23. Selected Additional Comments from INL Workshop (cont)
Steinberger (Forschungszentrum Jülich)
Types of Degradation Phenomena
• Baseline degradation (continuous, steady)
- Initialization phase (sintering, saturation)
- constant slope phase
- progressive degradation phase (EoL)
• degradation associated with transients
- thermal cycle
- redox cycle
• degradation after incidents (failures)
- malfunction of BoP components
- malfunction of control
- external influence (shock, grid outage etc.)

24. Selected Additional Comments from INL Workshop (cont)
Tang (Versa Power)
Improved Cell Investigation
• Demonstrated significant improvement from baseline TSC2 cells
• Completed 3000 hours SOEC/SOFC testing
• Degradation rate of 39 mV/1000 hours (3 ~ 4%)
Degradation Mechanism Study Indicated
• Combined SOEC/SOFC operation has significant higher (2x to 10x)
degradation rate compare to SOFC only operation
• Degradations from SOEC and SOFC are symmetrical
• Major cause of degradation (>90%) is the cell
• Interconnect degradation is less than 10%

25. Selected Additional Comments from INL Workshop (cont)
Singh (PNNL/UConn)
Bi-polar corrosion of interconnects
• Corrosion studies need to include both reducing and oxidizing environments on
either side of interconnects
Glass seals
• Reactions with metallic interconnects to form chromates
Hydrogen Electrode poisoning by Si

26. Conclusions and Research Plans
• System analysis results indicate excellent potential
for large-scale hydrogen production based on HTE
• Good initial and long-term cell performance is
critical to achieve competitive hydrogen
production costs
• INL HTE experimental program is now focused on
cell and stack performance issues:
– Development of improved cell compositions
(with Ceramatec)
– Evaluation of advanced electrode-supported
cells
– Demonstration of stable long-term performance

27. More Information is available in numerous publications
from our group!
Thank You!