The Solid State Energy Conversion Alliance · (CRC Handbook of Solid State Electrochemistry p. 505)...

U.S. Department of EnergyPacific Northwest National Laboratory

1

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


2

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


3

SECA Core Technology Program Activities at PNNL


4

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


5

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)

Oxy

gen

Sel

f D

iffu

sio

n C

oef

f. (

cm2/

s)

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


6

Temperature Dependence of Anode-supportedCell Performance

0

0.2

0.4

0.6

0.8

1

1.2

0 0.5 1 1.5 2

Current Density (A/cm2)

Vo

ltag

e (V

)

0

0.2

0.4

0.6

0.8

1

1.2

1.4

Po

wer

Den

sity

(W

/cm

2)

800ºC750ºC700ºC650ºC

Cell:

LSF Cathode / SDCInterlayer / YSZElectrolyte / Ni-YSZ anode

Fuel:

97% H2 / 3% H2O (LowFuel Utilization)

Oxidant:

Air


7

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

0

0.002

0.004

0.006

0.008

0.01

0.012

0.014

0 5 10 15 20 25 30 35

time (hours)

∆L/L

O

0

200

400

600

800

1000

1200

1400

1600

1800

2000I I IIII I

Tem

pera

ture

(o C

)

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)


8

“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

0.001

0 .01

0 .1

1

10

0 200 400 600 800 1000 1200

applied com pressive load, psi

lea

k r

ate

, sc

cm

SimpleMica Seal

“Advanced”Seals


9

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


10

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

Stack

Cell

Modeling levels

Con

tinuu

m-le

vel e

lect

roch

emis

try

Com

puta

tiona

l Too

lsfo

r The

rmal

Cyc

ling

Validation and Property measurement

Methane distributionCel

l-lev

el

Microstructure-level


11

• 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:


12

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

+=

23

23

22

22ln8 totCOOH

OCOHuo

PPP

PPP

FTR

EN

−− +⇒+ eCOOCO 222

−− ⇒+ 22 482 OeO

−− +⇒+ eOHOH 6333 22

2

Electrolyte Vn

Rn

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

lyte

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


15

Solid Oxide Fuel Cell Materials Researchat Argonne National Laboratory


16

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


17


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

LSF

PrSCSrCeF

SrCeC

0

5

10

15

Are

a S

peci

fic

Res

ista

nce/

Ω.c

m2

Temperature/°C

CathodeComposition

Time/Hours0 100 200 300 400 500

Are

al R

esis

tan

ce/Ω

. cm

2

0

1

2

3LSF(LS)0.8FLSFC


18


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


19


• 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


20


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


21

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

0.2

0.4

0.6

0.8

1.0

1.2

Slope = 0.140 Ω.cm2

Rohm

= 0.104 Ω.cm2

Slope = 0.084 Ω.cm2

Rohm

= 0.088 Ω.cm2


Vol

tage

(V

)

0.0

0.5

1.0

1.5

2.0

2.5

3.0

800 oC 100% O2 + 0% N2

21% O2 + 79% N2

Power D

ensity (W/cm

2)

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


22

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

0.02

0.04

0.06

0.08

0.10

0.12

0.14

0.16

O2-N

2 Effe

ctiv

e Di

ffusi

vity

thro

ugh

Por

ous

LSM

(cm

2 /s)

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

0.000

0.002

0.004

0.006

0.008

0.010

0.012

0.014

0.016

0.018

0.020

0.022

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

Cat

hode

Ove

rpot

entia

l (V)


Low DiffusivityHigh Polarization

Low Diffusivity

High DiffusivityLow Polarization

High Diffusivity

Funding: DOE/NETL

Cathode Concentration Polarization is SmallWhen Porosity is High


23

SOFC Cell Performance at Reduced TemperaturesSOFC Cell Performance at Reduced Temperatures

0

0.2

0.4

0.6

0.8

1

1.2

1.4

0 0.5 1 1.5 2 2.5 3

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

Cel

l Vol

tage

, V

0

0.2

0.4

0.6

0.8

1

1.2

1.4

Pow

er D

ensi

ty, W

/cm

2

80 0C

75 0C

70 0C

65 0C

60 0C

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

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


24

• 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

0.8

0.9

1

1.1

1.2

0 0.1 0.2 0.3 0.4 0.5 0.6 0.7

Current De nsity, A/cm2

Cel

l Vo

ltag

e (V

), F

uel U

tiliz

atio

n

0

0.1

0.2

0.3

0.4

PD, W

/cm

2

1 2 3 atmFuel uti li zation


25

YSZ film deposited from polymeric precursoron sapphire substrate

A) Annealed at 400°C for 4 hours

B) Annealed at 1000°C for 4 hours


26

P o r o u s C e O 2

Y S Z

P o r o u s C e O 2

Y S Z

P o r o u s L S M

Cross section - 1

Cross section - 2


27

3

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...


28

5

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)

YSZ

Ano

de

Met

alli

c S

upp

ort

Pt


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)

0

5

10

15

20

25

30

35

40

Iso-Octane Iso-Octane plus 20 % Xylene

Dodecane

% O

utle

t C

on

cent

rati

on

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

0

100

200

300

400

500

600

700

800

900

1000

3800 3820 3840 3860 3880 3900 3920 3940 3960 3980 4000

Time / sec

Ref

orm

er

Ou

tlet

Te

mp

era

ture

/ o

C

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

Reformer

Lightoff


32Fuel Cell Program

Fuel / Water co-vaporization Issues

60 0

65 0

70 0

75 0

80 0

85 0

90 0

95 0

100 0

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

form

er

Ou

tle

t T

em

pe

ratu

re /

oC

25 0

27 5

30 0

32 5

35 0

37 5

40 0

Fu

el

Inle

t T

em

pe

ratu

re /

oC

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

0

5

10

15

20

25

30

35

40

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

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

Lase

r A

bso

rptio

n (%

)

0

5

10

15

20

25

30

35

40

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

Re

lati

ve

Ab

so

rb


35

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

1”


36

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

0.005

0.01

0.015

0.02

0.025

0 100 200 300 400Temperature (°C)

H2S

Co

nc.

(p

pb

v)_

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)

Eq

uili

bri

um

H2S

C

on

cen

trat

ion

(p

pm

v)

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”


37

Fuel Processor - “APU”NETL Fuel Processing Team

E/MM0 680P GAR 3/00

NETL Fuel Processing TeamFuel Processor - “APU”

1”

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

Anode

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

800 °C

800 °C

650 °C


38

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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Transcript of The Solid State Energy Conversion Alliance · (CRC Handbook of Solid State Electrochemistry p. 505)...