Development and Characterisation of Metal-Supported Solid ...

Development and Characterisation of Metal-SupportedSolid Oxide Fuel Cells

G. Schiller

German Aerospace Center (DLR) Institute of Technical Thermodynamics

9th International Symposium on Advances in Electrochemical Science and Technology (ISAEST-9),December 2-4, 2010, Hotel Green Park, Chennai, India

ISAEST-9, December 2-4, 2010, Chennai, India

Outline

Introduction

German Aerospace Center (DLR)

SOFC Activities at DLR

Development of Metal Supported SOFC Concept of DLR

Development of Functional Layers and Cells

Electrochemical Cell Performance

Advanced Characterisation Techniques

Spatially Resolved Cell Characterisation

New Imaging Methods for SOFC Characterisation

Conclusions


DLRGerman Aerospace Center

Research InstitutionSpace AgencyProject Management Agency


Locations and Employees

6700 employees across 33 institutes and facilities at

13 sites.

Offices in Brussels, Paris and Washington.

Cologne

Oberpfaffenhofen

Braunschweig

Goettingen

Berlin

Bonn

Neustrelitz

Weilheim

Bremen Trauen

Lampoldshausen

Hamburg

Stuttgart


Research Areas

AeronauticsSpaceTransportEnergySpace AgencyProject Management Agency


DLR Site Stuttgart

Employees: 560Size of site: 25 860 m²Research institutes:

Institute of Structures and DesignInstitute of Vehicle ConceptsInstitute of Technical PhysicsInstitute of Technical ThermodynamicsInstitute of Combustion Technology


Solar Research Prof. Dr.-Ing. R. Pitz-Paal

Systems Analysis and Technology Assessment

Dr.-Ing. W. Krewitt

Electro-ChemicalEnergy Technology

Prof. Dr.rer.nat. A. Friedrich

Thermal ProcessTechnology

Dr.rer.nat. R.Tamme

Institute of Technical ThermodynamicsProf. Dr. Dr.-Ing. habil H.Müller-Steinhagen

Administration and Infrastructure

Dipl.-Wirt.Ing. J. Piskurek

Logistics & Purchasing

Project Administration

Computing Support

Workshops


SOFC Activities at

DLR

Characterization of Short Stacks and

Stacks (ASC, MSC)

Development of Metal Supported Cells (MSC)

System TechnologySOFC Diagnostics

Fuelgas Air

SOFC Modeling

H2H2/CO

CH4

H2OCO2

anode

electrolyte

cathode

O2/N2N2

interconnect

interconnect

Ri Resistor Si Switch, Ii Local current

Segmentvoltage,impedance

UlocalZlocal

Segmentcurrent

UIZ

Detailed 2D model of MEA, channel, interconnector

R1 R3 R4R2

R5 R7 R8R6

S1 S3 S4S2

S5 S7 S8S6

I4I3I2I1


R1 R3 R4R2

R5 R7 R8R6

S1 S3 S4S2

S5 S7 S8S6

I4I3I2I1

Cell current,voltage,

impedance


Development of Metal Supported Cells

LSM + YSZ

YSZ

Ni+YSZNi+YSZ

YSZ

LSM + YSZ

Ni+YSZ

YSZ

LSCF CGO

FeCr

YSZ/SSZ

LSCF CGO

Ni+YSZ

ESC ASC ASC MSC

Improved power density

Improved long-term stability

Reduced operating temperatureAdvantages of MSC:

• High robustness• High resistance against thermal and redox cycling• Good integration into interconnects (bipolar plates)• Low cost of metal support and cell materials (thin layers)


SOFC Metal Supported Cell

30 m

25 m

35 mBipolar plate

Bipolar plate

porous metallic substrateanodeelectrolyte

contact layercathode current collectorcathode active layer

protective coating

not used airoxygen/air

air channel

fuel channel

fuel brazing not used fuel + H O2

(not in scale)

Plasma Deposition Technology

Thin-Film Cells

Ferritic Substrates and Interconnects

Compact Design with Thin Metal Sheet Substrates

Brazing, Welding and Glass Seal as Joining and Sealing Technology


Vacuum Plasma Spraying of SOFC Cells


Plasma Spray Laboratory at DLR Stuttgart


Powders Used for the Spraying of the Cells

Powder NiO ZrO2-7 mol %Y2O3

ZrO2-10 mol%Sc2O3

(La0.8Sr0.2)0.98MnO3

Short name NiO YSZ ScSZ LSMMorphology sintered,

crushedsintered,crushed

sintered,crushed

sintered,spherical

Sizedistribution

10-25 µm 5-25 µm 2-35 µm 20-40 µm

Supplier Cerac,USA

Medicoat,Switzerland

Kerafol,Germany

EMPA,Switzerland


Morphology of Porous Metal Substrate PM Fe-26Cr-(Mo,Ti,Mn,Y2O3) of Plansee SE


Metallographic Cross Section of MSC Cell

Porously sintered ferrite plate

8YSZ-electrolyte

Ni/8YSZ-anode

La0.7Sr0.15Ca0.15CrO3-barrier layer

8YSZ-electrolyte

LaSrMnO3-cathode

Perovskite-type barrier layer


Plasma-spayed cell with sealing by laser welding

Stack Assembly Based on Metal Supported CellStack Assembly Based on Metal Supported Cell

1 = Metallic lower plate2 = Active cell on substrat 4 = Cassette 5 = Stack3 = Metallic frame


Stack Assembly Based on Metal Supported CellStack Assembly Based on Metal Supported Cell

Current MS-SOFC Repeat Unit

90x120 mm² footprint – ca 100 cm² cell area

Counter flow design

Stamped sheet ferritic steel bipolar plate

Welded Fe-Cr substrate

ISAEST-9, December 2-4, 2010, Chennai, IndiaVortrag > Autor > Dokumentname > Datum

Performance of Plasma Sprayed Metal Supported CellPerformance of Plasma Sprayed Metal Supported Cell

MSC Cell12.5 cm² cell at 800°C; H2/N2 and Air

3-Cell Stack100 cm² single cells at 800°C; H2/N2; Air


Thermal Cycling

15 thermal cycles performed, 12 down to 350 °C and 3 to ambient temperatureDegradation after thermal cycles was 10.3 %

Thermal cyclesMSC-02-17, 800°C

2 H2+2 N2/ 4 Air (SLPM)458 / 1227 h

0

200

400

600

800

1000

1200

0 50 100 150 200 250 300current density i [mA/cm²]

cell

volta

ge U

[mV]

0

50

100

150

200

250

300

350

400

pow

er d

ensi

ty p

[mW

/cm

²]

U1_startU2_startU1_endU2_endp1_startp2_startp1_endp2_end

p

U


Redox Cycling

20 forced redox cycles performed with 50 ml/min O2 on the anode side per layerIncrease of power density after 5 cyclesDegradation of the stack was 9.1 % after 20 redox cycles

Redox cycleMSC-02-17, 800°C

2 H2+2 N2/ 4 Air (SLPM)1227 / 1517 h

0

200

400

600

800

1000

1200

0 50 100 150 200 250 300current density i [mA/cm²]

cell

volta

ge U

[mV]

0

50

100

150

200

250

300

350

400

pow

er d

ensi

ty p

[mW

/cm

²]

U2_startU2_Redox_5

U2_Redox_20

p2_start

p2_Redox_5

p2_Redox_20

p

U

Redox_startcell2: 157 mW/cm²

Redox_5cell2: 177 mW/cm²

Redox_20cell2: 149 mW/cm²

Redox start @ 1,4 VPstack = 28,5 WFU = 14,1 mol%

Redox 5 @ 1,4 VPstack = 33,3 WFU = 16,6 mol%Redox 20 @ 1,4 VPstack = 26,0 WFU = 12,9 mol%


Investigation of Degradation and Cell Failures

Insufficient understanding of cell degradation and cell failures in SOFC

Extensive experimental experience is not generally available which would allow accurate analysis and improvements

Long term experiments are demanding and expensive

Only few tools and diagnostic methods available for developers due to the restrictions of the elevated temperatures


„Sophisticated“ (non-traditional) In-situ Diagnostics

Electrochemical impedance spectroscopy on stacks

Spatially resolved measuring techniques for current, voltage, temperature

and gas composition

Optical imaging

Optical spectroscopy

Acoustic emission detection

X-ray tomography


Motivation for Spatially Resolved Cell Characterisation

Problems: Strong local variation of gas composition, temperature, and current density

This may lead to:Reduced efficiencyThermomechanical stressDegradation of electrodes

Effects are difficult to understand due to the strong interdependence of gas composition, electrochemical performance and temperature


Measurement Setup for Segmented Cells

16 galvanically isolated segmentsLocal and global i-V characteristicsLocal and global impedance measurements

Local temperature measurementsLocal fuel concentrationsFlexible design: substrate-, anode-, and electrolyte-supported cellsCo- and counter-flow


Modelling and Simulation

Ri Resistor Si Switch, Ii Local current

Segmentvoltage,impedance

UlocalZlocal

Segmentcurrent

UIZ


R1 R3 R4R2

R5 R7 R8R6

S1 S3 S4S2

S5 S7 S8S6

I4I3I2I1


R1 R3 R4R2

R5 R7 R8R6

S1 S3 S4S2

S5 S7 S8S6

I4I3I2I1

Cell current,voltage,

impedance

H2H2/CO

CH4

H2OCO2

anode

electrolyte

cathode

O2/N2N2

interconnect

interconnect

Electrochemistry: Elementary kineticsPorous electrodes: Massand charge transportChannels: Transient Navier-Stokes conservationequations (Mass, momentum, particles, energy) Interconnects: energyconservation

W. G. Bessler, S. Gewies, and M. Vogler, Electrochimica Acta 53, 1782-1800 (2007)


Segmented Cells

Anode supported cells: Segmented cathode (H.C.Starck/InDEC)

Electrolyte supported cells: Segmented cathode and anode


Test Rig


OCV Voltage Measurement for Determination of Humidity

• Voltage distribution at standard flow rates:• 50% H2, 50% N2 + 3% H2O, 0.08 SlpM/cm² air

13 14 15 16

9 10 11 12

5 6 7 8

1 2 3 4

fuel gas air

22

20 lnHO

OHrevrev pp

pzFRTUU

Nernst equation:

Produced water:S4: 0.61%, S8: 0.72%, S12: 0.78%, S16: 3.30%


Power Density Distributution under Conditionsof High Fuel Utilisation

Counter-flow

Anode: 33% H2, 1% H2O,

66% N2

Cathode: air

T = 800 °C

Cell voltage: 0.59 V

Fu = 80%

Lit.: Fuel Cells, 10 (3), 411-418 (2010)


Assessment of Local Performance with Segmented SOFCs

Experiment

ModelUlocalZlocal

UIZ

UlocalZlocal

UIZ

16segments

Global Global behaviorbehavior

LocalLocalbehaviorbehavior

CellCell cancan bebe locallylocally in in criticalcritical conditionsconditions!!


Variation of Load - Reformate

Anode supported cell, LSCF cathode, 73,96 cm², gas concentrations (current density equivalent): 54.9% N2, 16.7% H2, 16.5% CO, 6,6% CH4, 2.2% CO2, 3.2% H2O (0.552 A/cm²), 0.02 SlpM/cm² air

0,0

50,0

100,0

150,0

200,0

250,0

300,0

Segment 9 Segment 10 Segment 11 Segment 12

pow

er d

ensi

ty p

[mW

/cm

²]

0,0

15,0

30,0

45,0

60,0

75,0

90,0

fuel

util

isat

ion

fu [%

]

p(i) 100 mA/cm² p(i) 200 mA/cm² p(i) 400 mA/cm² p(i) 435 mA/cm²

fu 100 mA/cm² fu 200 mA/cm² fu 400 mA/cm² fu 435 mA/cm²

fu

100

200

400435

100

200

400435

Pow

er d

ensi

tym

W/c

m2

Fuel

util

isat

ion

(%)


Alteration of the Gas Composition at 435 mA/cm²

0

0,05

0,1

0,15

0,2

0,25

0,3


Gas

konz

entra

tion

/ %

H2 CO CH4 CO2 H2O

Con

cent

ratio

n/ %

H2

10 11 12

CO

CH4

H2O

CO2

9


Alteration of the Gas Composition at 100 mA/cm²

0

0,05

0,1

0,15

0,2

0,25

0,3


Gas

konz

entra

tion

/ %

H2 CO CH4 CO2 H2O

KS4X050609-7 in Metallischem Gehäuse; Substrat: Anodensubstrat, aktive Zellfläche:73,78 cm²,A: 542 µm NiO/YSZ, E: 14 µm YSZ + YDC,

K: 28 µm LSCF, Kontaktierung: 30 µm LSP16+Pt3600,Integral, Gasflüsse: 0,552 A/cm² Stromdichteäquivalent (54,9% N2, 16,7% H2,

16,5% CO, 6,6%CH4, 2,2%CO2, 3,2% H20) // 0,08 SlpM/cm² Luft, 800 °C, 100 mA/cm²

Metallic housing, anode substrate, active area 73.78 cm²Anode: 542 µm NiO/YSZ, Electrolyte: 14 µm YSZ + YDC,Cathode: 28 µm LSCFOperation conditions: 0.10 A/cm² - Anode = 5.52(54.9% N2, 16.7% H2, 16.5% CO, 6.6% CH4, 2.2% CO2, 3.2% H2O0.08 Nlpm/cm² Air, 800°C)

Con

cent

ratio

n/ %

9 10 11 12

H2

CO

H2O CO2CH4


Potential for Optical Spectroscopies

Raman spectroscopyLaser Doppler Anemometry (LDA)Particle Image Velocimetry (PIV)Fast-Fourier Infrared (FTIR)Coherent Anti-Stokes Raman Spectroscopy (CARS)Electronic Speckle Pattern Interferometry (ESPI)

Digital CCD camera

Distance microscope(resolution1 µm)

Quarz window

Transparentflow field

Imagingspectrograph

Lenses/filter

Pulsed Nd:YAG laser(532 nm, 10 ns)

Open tube(5 mm)

a) In situ microscopy b) In situ Raman laser diagnostics

15 cm

Heat & radiation shield

SOFC


Setup for 1D-Raman Spectroscopy

3 double pulse Nd:YAG PIV 400 laser systemsλ = 532 nmRepetition rate: 10 HzSingle pulse: E ≤ 350 mJ / ~7 nsPulse energy: 6 x 300 mJ Pulse length: ~380 ns

(temporal resolution)


Transparent Flowfield for SOFC

Top view

Side view


Experimental Setup for Raman Spectroscopy Measurements


Cell Housing with Transparent Flowfield in Hot Furnace


Preliminary Results

Large scatter in detected signalImprovement of S/N ratio needed

H2 + 3% H2O850 °C


Preliminary Results

Measurements and evaluation still in progressTendencies of the species concentration profiles can be seen

H2 + 3% H2O850 °C


Setup for In-Situ Optical Microscopy


Conclusions

The development of the metal supported SOFC concept has a high potential for SOFC application in dynamic operation with multiple thermal and redoxcycles

Scale-up to a full size cassette with adequate cell performance is under way

In-situ diagnostic techniques allow for a largely extended insight into fuel cellprocesses

The obtained experimental data using a segmented cell setup that allows forthe measurement of local i-V characteristics, gas composition and temperaturecan be used for modeling and simulation

Strong gradients of gas concentrations and current density particularly at operation with high fuel utilisation may result in locally critical operatingconditions

Additional in-situ diagnostic methods such as optical microscopy and gas-phase Raman Spectroscopy can provide further information for theunderstanding of cell reactions and processes


Acknowledgment

I‘d like to thank my colleagues who contributed to this presentation:Asif AnsarCorinna AuerHolger AxWolfgang BesslerClaudia ChristennPatric SzaboCaroline Willichand all co-workers in our Department „Electrochemical Energy Technology“

Financial support from German Federal Ministry of Economics and fromState Ministry of Baden-Württemberg is gratefully acknowledged.


Locally Resolved Power Density Distribution and Fuel Utilisation in Dependence of H2 Concentrations

0.0

50.0

100.0

150.0

200.0

250.0

300.0

Segment5

Segment6

Segment7

Segment8

pow

erde

nsity

p[m

W/c

m²]

0.0

20.0

40.0

60.0

80.0

100.0

120.0

fuel

utilis

atio

nfu

[%]

p(i) 2%H2 p(i) 5%H2 p(i) 10%H2 p(i) 20%H2p(i) 50%H2 p(i) 100%H2 fu 2%H2 fu 5%H2fu 10%H2 fu 20%H2 fu 50%H2 fu 100%H2

fu

Development and Characterisation of Metal-Supported Solid ...

Documents

Transcript of Development and Characterisation of Metal-Supported Solid ...