RelHy International Workshop on High Temperature Electrolysis Limiting Factors

June 09-10, 2009 Karlsruhe, Germany

S. Elangovan, J. Hartvigsen, Feng Zhao, Insoo Bay, and Dennis Larsen

Office of Naval Research Contract: N00014-08-C-0680DOE subcontract through Idaho National Lab.

Energy, Environment & Economy• Environment

– Climate Change• GHG sources

– 8 tons CO2 /kW-yr from coal or oil– Leaky natural gas pipelines– Ruminants

• Ozone hole - no, that’s a different topic– Habitat Impacts

• Drilling in Arctic National Wildlife Refuge• Wind turbines in Chesapeake Bay

– Air pollution• Limited Resources

– Oil• National security

– Gas• Heating vs. power generation• Transportation issues

– Renewables

One Thing Is ClearEnergy Is The Key To Prosperity

Carbon Free Energy Source Options

http://www.eia.doe.gov/emeu/aer/pdf/pages/sec1_6.pdf

• Renewable energy resources– Large Scale Wind

• 800 GW at class 4+ US wind sites– Small Hydro

• 45GW potential, 2000 sites– Concentrator Photovoltaic

• Land area 12km2 /GW – Biomass

• Ag/Forestry byproduct• Carbon neutral cycle assuming production

and processing are carbon free• Nuclear

– 25 new plants announced– Increased output of existing units

• Note trend in figure since 1970

• Hydrogen production from electrolysis• High temperature 29 tons/GW-hr• Conventional 21 tons/GW-hr

Storing Hydrogen With CO2• Energy Sources

– Wind, Solar (PV & heat), Hydro, Nuclear• Carbon Sources

– Metallurgical Reduction, Cement Kilns– Fermentation, Digester gas– Biomass gasifiers– Fossil Power Systems

• Conversion Technology– SOFC electrolyzer, steam+CO2 => syngas

• Products– SNG, Fischer Tropsch liquids

Why Electrolytic Synfuels

• Electrolysis efficiency• Energy storage density• Fits in existing distribution infrastructure• Synergy with intermittent energy sources• No added CO2 emissions• Reduced work of compression• Compatible with existing vehicle fleet

– 20 to 50 year crossover

The New Alchemy: C ⇒ Au

• Turning carbon into gold– Low value carbon

• CO2 -$55/ton (Norway C tax)• Coal $20-100/ton• Bitumen ~ $100/ton

– High value carbon• Natural Gas $444/ton carbon

($7/decatherm)• Crude Oil $888/ton carbon ($105/bbl)• Refined fuel (pre-tax) ~$1000/ton carbon

Synthetic methane from electrolysis of CO2

From Electrolysis

FromMethanation

Unit

CH4 CO H2 CH4 CO H2

Test 1 .0 14.3 60.7 42.5 0 13.8

Test 2 .7 18.5 58.0 47.7 0 9.2

Test 3 .3 20.1 63.5 50.0 0 9.4

Test 4 .1 15.8 58.9 42.0 0 4.6

Test 5 .1 15.2 59.5 40.4 0 8.2

FEED TO ELECTROLYSIS IS CO2 + H2 O + ELECTRIC ENERGY

Gas analysis in volume %

FT- Liquid Products

• Ceramatec produced catalyst– FeCuK composition– 8mm La promoted alumina rings– Automated in-situ reduction

profile using dewpoint controlled temperature ramp

– Oil fraction– Water fraction

235°C Reactor Operation

One Technology - Multiple Modes Of Operation

Fuel

Solid Oxide Stack Module

Electricity

Steam +Electricity

Hydrogen(High Purity)

CO2 & Steam+ Electricity

SyngasNGBiogasDieselJP-8Coal

SOFC - SOEC Differences

• Cells tested to date are virtually identical– Same electrolyte, electrodes, pattern, etc.

• SOEC seals more challenging– Higher back pressure on seals due to product

collection – Low molecular weight stream vs. reformate

• Diffusion mechanism more active relative to hydrodynamic

• Hydrogen permeation in metal icon destabilizes air side scale

Sc - ZrO2 (partially stabilized)

Manganite + Zirconia Composite

Cobaltite (current distribution layer)

Ferritic Stainless Steel Separator

air electrode

electrolyte

Corrugated Ferritic Stainless Steel or High Ni alloy

H electrode

Ni + ceria cermet

50 µm50 µm

Ni (current distribution layer)

Corrugated Ni flow field on hydrogen side

Repeat Unit Elements

Stack Components

SOEC Limiting Factors• Degradation/Lifetime

– Oxygen bond layer stability– Oxygen electrode

delamination– Electrolyte stability– Chromium migration– Seals– Interconnect scale growth &

resistance– Electrode microstructure

• Electrode coarsening

• Cell Size & Stack Height– Very large cells feasible– Porous metal support

• Thermodynamics– Operating Voltage– Steam Utilization– Co-electrolysis of CO2

• High Temp Heat Duty– 0-15% of energy input– Wind hydrogen feasible

• Energy Cost– $50/MW-hr => $1.72/kg H2

• Amortized CAPEX– 24 month life => $0.46/kg H2

SOFC-SOEC Contrasts in (Potential:Composion) Space

Vtn

operating voltage, V

current density, A/cm2he

atflu

x,W

/cm2

-1.4-1.2-1-0.8-0.6-0.4

-0.3-0.2-0.100.10.20.30.4

-0.2

0

0.2

0.4

reactionohmicnet

thermal neutralvoltage

open-cellpotential

electrolysisfuel cell

Stack ASR = 1.25, T = 927 C, yH2,i = 0.1, yH2,o = 0.95

Vtn =−ΔhR

2F

(1.291 V at 1200 K)

Energy of fuel-cell vs. electrolysis mode

|<- 100% Efficiency Range ->|

Typical SOEC and SOFC Temperature Maps

SOFC ΔT > 90°CResistance doubling ~ 67 °CThermal expansion issues

System Efficiency vs. Steam+CO2 Utilization

INL Process Model shows little need tooperate with utilization much beyond 50%

Humidified CO2 Cell V-I CharacteristicCO2ELEC01:800°C

80F H2O, 45CC CO2, 8CC H2

y = -0.6907x + 0.8717

R2 = 0.9997

0.00

0.20

0.40

0.60

0.80

1.00

1.20

1.40

1.60

-0.80 -0.70 -0.60 -0.50 -0.40 -0.30 -0.20 -0.10 0.00 0.10 0.20 0.30

Current Density, A/cm^2

Vo

ltag

e,

Vo

lts

No reduction in performance compared to cells with steam electrolysis

Electrolysis Cells at 20cm Scale

Half ILS 2x60 Cell Stack Module

Pre-ILS Module Test at Ceramatec• “Half-ILS Module” test at Ceramatec

– Integrated Laboratory Scale (ILS) Demonstration– 2x60 cell stacks, 10x10 cm cells– Summer 2006, ~2000 hr operation– Cells & Stacks same as full ILS modules 2007,2008– Show performance scales with stack height– Assess system issues with tall stacks– Exercise component production capacity– Probably most extensive post test examination

• Tested component examination– ANL, MIT, UNLV, Ceramatec

Half ILS Initial Performance

– 3.8 kW– 1,200 Liters/hr– Electrical Efficiency = 96.4%– System thermal distribution issues– 2,000 hrs total operation– 1,000 hrs on CO2 /H2O

• Syngas production sufficient for 100 gallons of FT diesel

Half ILS module load history

Half-ILS Post-Test Observations• Electrodes

– Oxygen electrode delamination for 2,000 hr test• No delamination in short stacks tested for shorter periods (~300 hrs)

– Hydrogen electrode & current distribution layer in good condition• Electrolyte

– No cracking– Some cubic to tetragonal/mono-clinic transition noted

• Metal Interconnect Edge Corrosion– Edge rail coating & elimination of silica in seal eliminated the corrosion seen

in early SOEC stacks– Cr transport to air electrode bond layer– Sr migration from air electrode/bond layer

• Gross changes in bond layer chemistry, phase assemblage, conductivity and performance

• Initial Performance Reproducible – short to tall stacks• Unacceptably High Initial Degradation

720 Cell Full-ILS System at INL 5.7 Nm3/hr - 17.5kW H2 Production

Full-ILS Module #3 Post Test Examination

Oxygen electrode delamination

Hydrogen electrode attached,bond layer separated with icon

ILS Module #3 Post Test Examination

Oxygen electrode and iconcontacting layer (bond layer)

It appears a layer depositedat electrode interface is causingthe delamination

ILS Module #3 Post Test Examination

EDS Indicates only ScSz at theinterface. The apparent depositionlayer is a layer of zirconia thathas spalled off. Our hypothesis isthat Mn diffusing in from the manganite electrode introducesenough electronic conductivityto allow oxygen to evolve insidethe electrolyte, build up pressureand split off a layer near theelectrode.

ILS Module #3 Post Test Examination

Cobaltite (LSCo) iconcontacting layer (bond layer)

Manganite-Zirconia Composite

Manganite Electrode

Electrode section in following EDS Maps

Co-Mn Inter-diffusion in Oxygen Electrode

SOFC Button Cell (early - mid ‘90s)

Fully stabilized custom electrolyte from undoped zirconia LaSrMnO3 ; Ni-YSZ

SOFC Button Cell (2002)

YSZ electrolyte; Ni-ceria anode; modified manganite

SOFC Stack (1996)

YSZ electrolyte; Ni-ceria; Modified manganite; ceramic interconnect (doped lanthanum chromite)

Prioritized Areas of Focus• O2 Electrode Delamination – inherent to SOEC operation?

– Electronic conductivity due to Mn diffusion into electrolyte• Barrier layer & alternative compositions

• O2 Electrode Bond Layer Stability– Sintering-shrinkage, phase change, Cr tol, stoichiometry changes

• O2 Electrode Chromium Poisoning– Solid state diffusion by interconnect contact

• CrMn & CuMn spinel coatings

– Evaporation/Condensation from interconnect, manifold, piping

• Electrolyte Stability– Minimum dopant level (strength trade-off)– How much degradation is allowable

• System BOP Reliability• Seal Stability

Electrolyte Composition Effect

Fully Stabilized (FS-ScSZ) Cell Performance

30% Reduction in initial ASRvs. PS-ScSZ

Initial O2 Electrode Microstructure

Initial O2 Electrode Microstructure

Initial H2 Electrode Microstructure

Initial H2 Electrode Microstructure

Hydrogen Electrode & Bond Layer

Adherent and conductive hydrogen electrodeMost areas of bond layer separated with flowfield

Oxygen Electrode and Bond Layer

Extensive delamination of standard manganite Perovskite electrodes

No delamination of new cobalt-ferrite Perovskite electrodes

O2 Electrode Comparison Stack

New O2 Electrode Improves Stack Stability

Metal Interconnect Contact Resistance

• Leverage decades of SOFC R&D• Inputs

– e- (green electrons)– steam => hydrogen– co-electrolysis of H2 O + CO2 => syngas– heat input optional, depends on operating point

• Most efficiency means of hydrogen production– e- to hydrogen

• η=100% at 1.285V• η= 95% at 1.35V• η=107% at 1.20V, (heat required)

• Hot O2 and steam byproduct– Valuable for biomass gasification

High Temperature Electrolysis