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transcript
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