the solid state energy conversion alliance · (crc handbook of solid state electrochemistry p. 505)...

U.S. Department of EnergyPacific Northwest National Laboratory

The Solid State Energy Conversion Alliance

March 21-22, 2002Washington, D.C.

www.netl.doe.gov/scng

Wayne A. SurdovalSECA Program Coordinator

SECA Core Technology Program

Third Annual SECA Workshop

Descriptor - include initials, /org#/date

SECA Core Technology Program Solicitation• Fuel Processing

− Contaminant Resistant Anodes and Reforming Catalysts for IntermediateTemperature Solid Oxide Fuel Cell Systems

− High Temperature Sulfur Removal

• Manufacturing− Low Cost Production of Precursor Materials

• Controls and Diagnostics− Sensors− Active Sealing Systems

• Power Electronics−Interaction Between Fuel Cell, Power Conditioning Systems and Application

Loads− DC-to-DC Converters for Solid-Oxide Fuel Cells

• Modeling & Simulation− Fuel Cell Failure Analysis− Manufacturing Models

• Materials− Cathodes− Interconnects− Innovative Sealing Concepts

SECA Core Technology Program Activities at PNNL

Core Technology - Areas of Emphasis

• SOFC component development• Anode Supported Cell Fabrication & Performance Optimization

• Tape casting process• Anode & cathode materials• Interconnects• Seals

• SOFC modeling• Modeling of cells and stacks – transient and steady state• System modeling

Advantages of LSF Cathode

1.00E-16

1.00E-14

1.00E-12

1.00E-10

1.00E-08

1.00E-06

1.00E-04

1.00E-02

1.00E+00

600 700 800 900 1000 1100

Temperature (C)

LSM-50

LSCo-20

LSCo-10

LSF-10

LSF-40

LCCF-6482

LSCN-6482

LSCF-6428

LSCF-4628

Data from PNNL (LSCF compositions) and others(CRC Handbook of Solid State Electrochemistryp. 505)

High oxygen diffusioncoefficient (relative to LSM)increases “effective” TPB atthe cathode / electrolyteinterface, thereby reducing thecathode overpotential

Other advantages of LSFas cathode material:

High oxygen surface exchangecoefficient; TEC is compatiblewith other cell components;high electronic conductivity

Temperature Dependence of Anode-supportedCell Performance

0 0.5 1 1.5 2

Current Density (A/cm2)

800ºC750ºC700ºC650ºC

LSF Cathode / SDCInterlayer / YSZElectrolyte / Ni-YSZ anode

97% H2 / 3% H2O (LowFuel Utilization)

Oxidant:

Advanced Red/Ox Tolerant AnodeDoped SrTiO3 compositions show promise as red-ox tolerant anodematerials

0 5 10 15 20 25 30 35

time (hours)

∆L/L

2000I I IIII I

Simulated Thermal Cycles-

I: Exposure to reducingenvironment at 1000ºC(corresponding to SOFCanode environment duringoperation)

II: Exposure to air duringthermal cycling(corresponding to conditionsan unprotected anode wouldexperience during sytemstartup and shutdown)

“Advanced” compressive seal conceptIn coupon testing, mica gaskets exhibited relatively high leak rates undermoderate compressive loads. In recent testing, advanced compressive sealsexhibited leak rates approximately 2 orders of magnitude lower relative tosimple mica gasket. Test conditions: 800ºC in air

0 200 400 600 800 1000 1200

applied com pressive load, psi

SimpleMica Seal

“Advanced”Seals

Metallic Interconnect Development3-step Screening & Testing Study to Evaluate Candidate Alloys Goals: Identify candidate alloys for SOFC interconnect; Develop

understanding of corrosion processes and mechanisms

Step 1 – completed – compiled metallurgical database; reducedcandidate list from ~300 to ~15 alloys

Step 2 – in progress – screening tests• chemical – stability in fuel and oxidant environment, compatibility

and bonding strength with seal materials• electrical – effects of environment on scale resistance• mechanical – effects of environment on mechanical properties• fabrication – formability and joinability testing

Overview of Modeling and SimulationsFlow Analysis

Thermal Analysis

Stress Analysis

Flow, thermal &Electrochemistry analysis

Temperature profile

H2O concentration

Thermal Shock

Electrical Power System

Thermal system

Modeling levels

Validation and Property measurement

Methane distributionCel

Microstructure-level

• Low cost tape casting process for anode & electrolyte fabrication• Single step sintering process for anode-supported electrolyte co-

sintering• Non-nickel base anode for oxygen tolerance• Sr doped lanthanum ferrite cathode electrode for superior

performance• Engineering performance models for cell & stack operations• Data base compilation for candidate metallic current collector

Accomplishments:

SECA Worksho p (war ) / M arch 2 1, 20 02

• Three-dimensional, steady-state, with fluid dynamics, heattransfer, species transport, chemical reaction, porous media flow

− Water-gas shift reaction

− Species diffusion in flow channels and porous media

• Electrochemical SOFC submodel

− H2 and CO Electrochemistry

• Electrical field submodel to calculate electrical potential field in allconducting regions including electrodes, current collectors,interconnects

− Ohmic heat generation

− Current Flow

• Parallel Code for PC cluster computing

• Model temperature output coupled to ANSYS FEA code for stressanalysis

NETL SOFC Model Capabilities

22ln8 totCOOH

OCOHuo

−− +⇒+ eCOOCO 222

−− ⇒+ 22 482 OeO

−− +⇒+ eOHOH 6333 22

Electrolyte Vn

InAnode

Cat hode

Vn = Nernst Pot entia l - Ov erpotent ialsRn = Loc al Lumped Resistance (ohmic +electroc hemical losses)

ii ρ=⋅∇φσ∇−=i

SECA Worksho p (war ) / M arch 2 1, 20 02

Example: Simple Co-Flow Channel

Current Density onElectrolyte-Cathode Face(Amp/m2)

Anode Current Col lectorAnode Current Col lector

Cathode CurrentCathode CurrentCol lectorCol lector

CathodeCathodeAnodeAnode

Electr o

Fuel InFuel In

Fuel OutFuel Out

Oxidizer InOxidizer In

Oxi dizerOxi dizerOutOut

Displacement

Stresses

SECA Workshop (war) / March 21, 2002

•• Extend to StacksExtend to Stacks•• Internal ReformingInternal Reforming•• Include Contact ResistanceInclude Contact Resistance

−− Current collector-electrode−− Electrode-electrolyte−− Current collector-interconnect

•• Complete Model ValidationComplete Model Validation−− Data from open literatureData from open literature−− Data from NETL testing facilitiesData from NETL testing facilities−− Data from SECA partnersData from SECA partners

•• Working with SECA partners in Model Validation and ApplicationWorking with SECA partners in Model Validation and Application−− DelphiDelphi−− SiemensSiemens-Westinghouse-Westinghouse

Planned Capabilities and Validation

Solid Oxide Fuel Cell Materials Researchat Argonne National Laboratory

Argonne Elec trochemical Technology Program

Drivers for the research• A major approach to lowering fuel cell and balance-of-

plant costs is to reduce SOFC operating temperaturesto <800oC. At the lower temperatures, however,

– Conventional LSM cathode performance is inadequate• Need to develop perovskite and other cathode materials with

high electrochemical activity, low resistivity at <800oC

– Sulfur-poisoning of Ni anode is exacerbated• Need anode materials tolerant to 1-100 ppm or more of H2S

– Metallic interconnect (bipolar) plates become feasible• Need new alloys or coatings as presently available metals

and alloys degrade rapidly in SOFC environments

Low-Temperature Cathode Materials

Single-phase cathode materials• Accomplishments

– Identified Sr-doped lanthanum ferrates as themost promising candidate cathode materials

– Verified stable performance to 500 h

650 700 750 800 850

PrSCSrCeF

Temperature/°C

CathodeComposition

Time/Hours0 100 200 300 400 500

3LSF(LS)0.8FLSFC

Metallic Interconnect Materials

Approach• Alloys similar to ferritic stainless steels

– reduce Cr, other elements that can degrade fuel cellperformance

– additives to improve properties and protective scale

• Materials of graded composition to impart optimumchemical stability at each surface

• Novel processing technique can yield almost anydesired shape– flat, corrugated, textured, functionally graded

– can incorporate flow fields, internal manifoldsFormed

Flow Fieldin DenseMaterial

MacroporousFlow Field

Formed FlowField withPorousLayers

• 10-Layer specimenTwo surface layers:

Fe-Cr-La-Y-Sr alloyBulk: SS Type 434

• Points 1,2: ~1.5 - 2.0 wt% La

• Points 3,4: no measurable La

Metallic Interconnect Materials

Multi-layer plates are easily formed

• Compositionally graded specimens can be fabricated• Samples show excellent bonding• After 400 h at 800oC, there was no observed elemental

diffusion between layers

SEM Micrograph of compositionally-graded sample

SummaryFuture directions

• Micro-engineer the cathode-electrolyteinterface to further improve cathodeperformance

• Evaluate anode materials with 0-100 ppmH2S in fuel gas

• Characterize oxide scale on metallic bipolarplates for growth rates and electricalconductivity

• Test developed materials in full cell andshort stack configurations

Effect of Oxidant Composition on a High Performance,Anode-Supported Cell

0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5 5.0 5.5 6.00.0

Slope = 0.140 Ω.cm2

= 0.104 Ω.cm2

Slope = 0.084 Ω.cm2

= 0.088 Ω.cm2

800 oC 100% O2 + 0% N2

21% O2 + 79% N2

Power D

ensity (W/cm

MPD ~2.9 W/cm2

With H2/O2

Funding: DOE/NETL

MPD ~1.75 W/cm2

With H2/Air

Good Cathode:But Needs to beBetter

O2-N2 Effective Diffusivity through Porous LSM andCathodic Concentration Polarization

Experimentally MeasuredEffective Diffusivities

Calculated CathodicConcentration Polarization

Thickness = 50 µmPorosity created by adding carbon, andburning it off.

0.10 0.15 0.20 0.25 0.30 0.35 0.40 0.45 0.500.00

2 Effe

Open Porosity0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.6 1.8 2.0 2.2

20 wt% C 22.5 wt% C 25 wt% C 27.5 wt% C 30 wt% C

Low DiffusivityHigh Polarization

Low Diffusivity

High DiffusivityLow Polarization

High Diffusivity

Funding: DOE/NETL

Cathode Concentration Polarization is SmallWhen Porosity is High

SOFC Cell Performance at Reduced TemperaturesSOFC Cell Performance at Reduced Temperatures

0 0.5 1 1.5 2 2.5 3

C ur r ent De ns it y, A/ cm 2

Hydrogen fuel

Air oxidant

• High power densities (e.g., 0.9 W/cm² at 650°C) achieved at reducedtemperatures (<800°C) with anode-supported thin-electrolyte cells

• First pressurized SOFC with planar anode-supported thin-electrolyte cells• First pressurized SOFC with planar anode-supported thin-electrolyte cells

Pressurized Operation of Planar Pressurized Operation of Planar SOFCsSOFCs

Expe rimental Data Points and Mode l

0 0.1 0.2 0.3 0.4 0.5 0.6 0.7

Current De nsity, A/cm2

1 2 3 atmFuel uti li zation

YSZ film deposited from polymeric precursoron sapphire substrate

A) Annealed at 400°C for 4 hours

B) Annealed at 1000°C for 4 hours

P o r o u s C e O 2

P o r o u s L S M

Cross section - 1

Cross section - 2

LBNL Developed Colloidal Deposition Technique for SOFCsLBNL Developed Colloidal Deposition Technique for SOFCs

NiO/YSZ substrate(pressed)

NiO/YSZ firedat 950 oC

NiO/YSZsubstra te with

green YSZ film

NiO/YSZ-YSZbilayer fired at

1400 oC

•Geometry Independent•Low Cost•Scaleable

Dip-coat, aerosol spray, EPD...

Development of Alloy Supported Thin-film SOFCStructures to Reduce Stack Cost and Improve Reliability

Top view of a YSZ/Ni-YSZ/FeCr alloy SOFCbilayer (lookingthrough transparentYSZ film).

Bottom view of aYSZ/Ni-YSZ/FeCralloy SOFCbilayer (at porousFeCr electrode)

29Fuel Cell Program

Objectives and TasksObjectives: Develop technology leading to reforming of diesel fuel for APU applications. Understand parameters that affect fuel processor lifetime and durability.

Examine fuel components, impurities and additives Quantify fuel effects on fuel processor performance Understand the parameters that affect fuel processor lifetime and durability

Catalyst durability Carbon formation and catalyst durability

Tasks: Carbon Formation Measurement of Diesel Fuel(s)

Equilibrium and component modeling Experimental carbon formation measurement

Fuel MixingVaporization / Fuel atomization Direct liquid injection

‘Waterless’ Partial Oxidation of Diesel Fuel Start-up SOFC anode recycle

30Fuel Cell Program

Partial Oxidation Stage Outlet Concentrations(for similar oxygen conversion)

Iso-Octane Iso-Octane plus 20 % Xylene

Dodecane

H2+COUnconverted O2

Higher Temperatures (O/C ratio’s) are required for long chainedhydrocarbon conversion for similar residence times – leads to H2 dilution

Longer residence times required for similar conversion (same Temperature / O/C)residence time (iso-octane ~ 10 msec)residence time (dodecane ~ 45 msec)

31Fuel Cell Program

Diesel POx/Reforming Light-off

3800 3820 3840 3860 3880 3900 3920 3940 3960 3980 4000

Time / sec

Reactor start-up with kerosene / no waterwater availability during initial operation

Reformer

Lightoff

32Fuel Cell Program

Fuel / Water co-vaporization Issues

1 500 0 1 510 0 1 520 0 1 530 0 1 540 0 1 550 0 1 560 0 1 570 0 1 580 0 1 590 0 1 600 0

Time / sec

Re for me r Te mpe ra ture deg CR ea ctor F u el In let Te mpe ra ture deg C

Co-vaporization of water and fuel in external vaporizeruses water as carbon formation suppressant / fuel carrier

Co-vaporization produces periodic ‘distillation’ and reactor temperature exotherms

Reactor outlet temperature

Vaporizer outlet temperature

33Fuel Cell Program

• Catalytic oxidation / reforming• Diesel Fuel Components (Dodecane)

• Long chained hydrocarbons require higher residence time for conversion• aromatics slow and inhibit overall reaction rate

• Pre-combustion

• Diesel fuels much more likely for pre-combustion• Kerosene has higher pre-combustion tendencies than de-odorized

kerosene

• Carbon Formation• Hysteresis observed after on-set of carbon formation• Greater carbon formation with aromatics

Technical Summary/Findings

34Fuel Cell Program

Technical Results:Carbon formation measurements

Results• Partial oxidation of

• odorless kerosene• kerosene• dodecane• hexadecane

• Carbon formationmonitoring by laser optics• Carbon formation shownat low relative O/C ratiosand temperature withkerosene (left)• Demonstrated start-upwith no water – carbonformation observed after ~100 hrs of operation

Carbon formation monitoring with laser scatteringOdorless Kerosene; S/C = 1.0

6 70 6 80 6 90 7 00 7 10 7 20 7 30

Ad iab atic Re acto r Outl et Temperature (oC)

0. 2 0. 4 0. 6 0. 8 1O / C R a ti o

E/MM0680P GAR 3/00

• Challenge: Limited sulfur tolerance in fuel cell reformer & stack• NETL Research: Selective Catalytic Oxidation of H 2S• Benefit: Fuel cells using coal gas, nat. gas, transportation fuels

NETL Fuel Processing TeamFuel Desulfurization - “SCOHS”

H2S + 1/2 (O2 + 3.76 N2) = 1/n Sn + H2O + 1.88 N2

Sulfur productcontinuouslydrips out.

NETLSCOHS Catalyst

E/MM0680P GAR 3/00

• Removal Efficiency: SCOHS has part per trillion (ppt)thermodynamic sulfur removal efficiencies.

• Water Sensitivity: Unlike most metal oxide based systems,SCOHS is relatively insensitive to water content, which can befound in high concentrations in some reformate streams.

0 100 200 300 400Temperature (°C)

H2O/H2S = 0.0

H2O/H2S = 1.0

H2O/H2S = 10

H2O/H2S = 1001.00E-07

1.00E-06

1.00E-05

1.00E-04

1.00E-03

1.00E-02

1.00E-01

1.00E+00

1.00E+01

1.00E+02

1.00E+03

1.00E+04

0 200 400 600 800 1000 1200Temperature (o C)

0.1% 0.5% 1% 2% 5% 10% 20% 40%H2O

Content

0.1 ppmvSOFC

Zinc Titanate - Thermodynamic Removal Eff.SCOHS - Thermodynamic Removal Eff.

NETL Fuel Processing TeamFuel Desulfurization - “SCOHS”

Fuel Processor - “APU”NETL Fuel Processing Team

E/MM0 680P GAR 3/00

NETL Fuel Processing TeamFuel Processor - “APU”

DesulfurizerTemperature

150/400 C 800 C

Efficiency 52.82 55.09

Net Power Output 5 kW 5 kW

Mass Specific FuelConsumption

.75E-3kgmol / kW hr

.722E-3kgmol / kW hr

ATR Oxygen-to-Carbon Ratio - 0.25ATR Steam-to-Carbon Ratio - 0.7Fuel Cell / Reformer Temperature - 800 C

FuelCellStack

Cathode

Combustor

AutoThermalReformer

Desulfurizer Sorbent Bed

Exhaust Condenser

Steam Generator

Air PreheaterAir Compressor

Fuel Pump

Water Pump

800 C SECA APU

800 °C 800 °C

800 °C

650 °C

Descriptor - include initials, /org#/date

Additional SECA Core Program Participants

Don Adams

Descr ip tor - include initials, /o rg#/ date

Technology Management, Inc.Benson Lee

Demonstrate the operation of two SOFC modules as a s ingle unit.

Develop Screen Printing Manufacturing Technique

University of FloridaEric Wachsman

Develop Bi-Layer Ceria, Bismuth Oxide electrolyte for low temperature operation. Develop ionic conduction model.

Northwestern University/Applied Thin FilmsScott Barnett

Develop segmented in series SOFC design.Develop internally reforming anode as discussed in “Nature”

Georgia Institute of Technology/ Meilin Liu

Development of ultra-low (500 C) temperature SOFC materials.Development of in-situ FTIR emission spectroscopy forevaluation of gas-solid interactions in fuel cells.

NexTech Materials, Ltd.Bill Dawson

Development of cathode supported SOFC designs.Development of manufacturing techniques for low temperature SOFC materials

CeramatecS. E langovan

InterconnectsDevelopment of Low Temperature material set.

Oak Ridge National LabEdgar Laura-CurzioDon Adams

SOFC material property and reliability eva luationsPower Electronics evaluat ion.

the solid state energy conversion alliance · (crc handbook of solid state electrochemistry p. 505)...

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