RelHy Workshop on High Temperature Water Electrolysis Limiting Factors

June 9 – 10, 2009

J. E. O’Brien

The High-Temperature Electrolysis Program at INL: Observations on Performance Degradation and Summary of INL-Sponsored Degradation Workshop

C. M. Stoots, J. S. Herring, K. G. Condie, G. K. Housley, M. G. McKellar, M. S. Sohal, J. J. Hartvigsen

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

Experimental

CFD Simulation

Demonstration and Scale-Up

System Modeling

INL HTE Research Scope

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

System Modeling

0.44

0.46

0.48

0.5

0.52

0.54

1 1.05 1.1 1.15 1.2 1.25 1.3 1.35 1.4

per-cell operating voltage

over

all h

ydro

gen

prod

uctio

n ef

ficie

ncy

(LH

V)air swp, adiabatic, ASR 0.25air swp, adiabatic, ASR 1.25air swp, isothermal, ASR 0.25air swp, isothermal, ASR 1.25no swp, adiabatic, ASR 0.25no swp, adiabatic, ASR 1.25no swp, isothermal, ASR 0.25no swp, isothermal, ASR 1.25simple thermo analysis

The red line follows from the definition of the overall thermal-to-hydrogen efficiency and direct application of the first law

HHVFVLHV

thopH +−=

)1/1(2 ηη

∑=

ii

H QLHVη

Overall Hydrogen Production Efficiencies, HTE Reference Case, as a function of Cell Voltage

System Analysis Results

System Analysis Results

0.2

0.25

0.3

0.35

0.4

0.45

0.5

0 20 40 60 80 100

adiabatic, ASR 0.25adiabatic, ASR 1.25isothermal, ASR 0.25isothermal, ASR 1.25

over

all h

ydro

gen

prod

uctio

n ef

ficie

ncy

Steam Utilization

Overall Hydrogen Production Efficiencies

HTE Reference Case (air sweep)

vs Hydrogen Production Rate vs Steam Utilization

(imax corresponds to Vtn )

0.44

0.45

0.46

0.47

0.48

0.49

0.5

0.51

0 0.5 1 1.5 2 2.5

adiabatic, ASR 1.25isothermal, ASR 1.25adiabatic, ASR 0.25isothermal, ASR 0.25

over

all h

ydro

gen

prod

uctio

n ef

ficie

ncy

hydrogen production rate, kg/s

Note: the high-ASR cases shown here require ~ four times as many cells.

hydrogen production rate, m3/hr0 20,000 40,000 60,000 80,000 100,000

fixed utilization

System Analysis Results

Overall Hydrogen Production Efficiencies

Dependence on Reactor Type and Outlet Temperature

0

10

20

30

40

50

60

300 400 500 600 700 800 900 1000

T (°C)

Ove

rall

ther

mal

to h

ydro

gen

effic

ienc

y (%

)

65% of max possibleINL, HTE / He Recup BraytonINL, LTE / He Recup BraytonINL, HTE / Na-cooled RankineINL, LTE / Na-cooled RankineINL, HTE / Sprcrt CO2INL, LTE / Sprcrt CO2SI Process (GA)MIT - GT-MHR/HTEMIT AGR -SCO2/HTE

HTE Experimental Program

INL High-temperature electrolysis laboratory

Small-scale experiments Integrated Laboratory Scale Facility (15 kW)

Schematic of single-cell electrolysis test apparatus

HTE Experimental Program

Exploded view of Ceramatec electrolysis stack components

HTE Experimental Program

HTE Experimental Program

-1.6

-1.4

-1.2

-1

-0.8 -1

-0.7

-0.4

-0.1

0.2

-0.6 -0.4 -0.2 0 0.2

E1E2E3E4E5E6

p1p2p3p4p5p6

cell

pote

ntia

l, E

(V)

cell power density, p (W

/cm2)

current density, i ( A/cm2)

fuel cell modeelectrolysis mode

Tdp,i

(C)Tfrn

(C)sweep25.4800125.6850234.3800334.4850447.2800547.98506

power densitycell potential0

Qs, Ar

= 140 sccm

Qs, H2

= 40.1 sccm

Tf (C)T

dp, i (C)sccm H2sccm N2sweep #

80048.5205101110-180070.4411201710-280083.8410101710-380082.9411201810-483083.2411201810-580083.8513201325-183083.4513201325-2

0.8

0.9

1

1.1

1.2

1.3

1.4

1.5

0 0.05 0.1 0.15 0.2 0.25 0.3 0.35

per-

cell

oper

atin

g vo

ltage

, V

current density, i (A/cm2)

10-1

10-2

10-3

10-4

10-5theoretical open-cell potentials

25-1

25-2

0

5

10

15

20

0 2 4 6 8 10 12 14

Mol

e %

(Dry

Bas

is)

Electrolysis Current (A)

Inlet CO2

Inlet CO

H2

CO

CO2

Inlet H2

Outlet gas composition as a function of current density for co-electrolysis experiments, 10-cell stack

Cell Performance Characterization: Polarization curvesButton cell stack

0.2

0.4

0.6

0.8

1

1.2

1.4

0 200 400 600 800 1000 1200

ASR

elapsed time, hr

OCV check

0.8

1.2

1.6

2

2.4

0 200 400 600 800 1000

ASR

, Ohm

cm

2

elapsed time, hrs

increased furnace temperature from 800 C to 830 C

HTE Experimental Program

Cell and Stack Performance Degradation

Area-specific resistance vs time over ~ 1000 hrs

Single button cell Stack

ANL Post-Test Examination of Ceramatec Cells (D.Carter, J. Mawdsley)

Electrolyte

O2 Electrode

SEM view of the electrolyte and oxygen electrode showing delamination and cracks

Chromium deposition in SOEC and SOFC modes (more uniformly dispersed in SOEC mode)

Silica capping layer on H2-electrode

Si is carried by steam from the Si-bearing seal; can also originate from interconnect plate

ANL Post-Test Examination of Ceramatec Cells (D.Carter, J. Mawdsley)

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

ILS hydrogen production rate time history

HTE Experimental ProgramIntegrated Laboratory Scale Facility

Initial production rate in excess of 5 m3/hr, followed by serious degradation, some of which was related to BoP issues

Ceramatec Post-Test Examination of ILS Cells

electrolyte

Oxygen electrode

Cell and interconnect surfaces from the oxygen electrode side of ILS Cell, showing delamination

Performance Improvement: Single-cell test stand (electrode-supported cells)

HTE Experimental Program

Exploded view Assembly view Photo

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.

Summary of INL Workshop Discussion on SOEC

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

Degradation Mechanisms

Mitigation Strategies1. 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, materials5. Use fully stabilized mixture, add ceria or alumina6. Improved seals, CTE match, all-ceramic cells and stacks

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

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.)

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%

Selected Additional Comments from INL Workshop (cont)

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 interconnectsGlass seals

• Reactions with metallic interconnects to form chromates

Hydrogen Electrode poisoning by Si

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

More Information is available in numerous publications from our group!

Thank You!