impedance spectroscopy as a diagnosis tool for sofc stacks and
TRANSCRIPT
IWEslide: 1, 9/17/2009source: 2009-06-24 EIS Diagnosis for Stacks.ppt,
Universität Karlsruhe (TH)Institut für Werkstoffe der Elektrotechnik
International Symposium onDiagnostics Tools for Fuel Cell Technologies
Impedance Spectroscopy as a Diagnosis Tool for SOFC Stacks and Systems
André Weber, Dino Klotz, Volker Sonn, Ellen Ivers-Tiffée
Institut für Werkstoffe der Elektrotechnik (IWE)Universität Karlsruhe (TH)
Adenauerring 20b, 76131 Karlsruhe, Germany
IWE
IWEslide: 2, 9/17/2009source: 2009-06-24 EIS Diagnosis for Stacks.ppt,
Universität Karlsruhe (TH)Institut für Werkstoffe der Elektrotechnik
ENBW, Delphi
Control an Diagnosis of SOFC-Stacks and SystemsStack Monitoring by Impedance Spectroscopy
Control of parameters critical for a failure free operation of stack and system
Monitoring of the internal resistance of the stack by electrochemical impedance spectroscopy
• stack performance and efficiency• stack temperature(s)• reformer temperature(s)• steam to carbon ratio / λPOx-value• fuel (reformate) composition• oxidant and fuel flow rates• oxidant and fuel temperatures at gas inlet• oxidant and fuel pressures at gas inlet• exhaust gas composition (remaining CO, HC´s)• ...
• stack performance and efficiency• stack temperature(s)• reformer temperature(s)• actual steam to carbon ratio / λPOx-value• fuel (reformate) composition• oxidant and fuel flow rates• oxidant and fuel temperatures at gas inlet• oxidant and fuel pressure inlet• exhaust gas composition (remaining CO, HC´s)• ...
IWEslide: 3, 9/17/2009source: 2009-06-24 EIS Diagnosis for Stacks.ppt,
Universität Karlsruhe (TH)Institut für Werkstoffe der Elektrotechnik
Electrochemical Impedance Spectroscopy
H. Gerischer, Elektrodenpolarisation bei Überlagerung von Wechselstrom und Gleichstrom. Z. Elektrochem., 58, 9, 278, 1954
see above
Impedance Spectroscopy Materials, (Model-) Electrodes and Single Cells
IWEslide: 4, 9/17/2009source: 2009-06-24 EIS Diagnosis for Stacks.ppt,
Universität Karlsruhe (TH)Institut für Werkstoffe der Elektrotechnik
Electrochemical Impedance Spectroscopy
H. Gerischer, Elektrodenpolarisation bei Überlagerung von Wechselstrom und Gleichstrom. Z. Elektrochem., 58, 9, 278, 1954
Analysis of Solid Electrolytes by Impedance Spectroscopy
J. E. Bauerle, Study of solid electrolyte polarization by a complex admittance method, J. Phys. Chem. Solids 30, 2657, 1969
see above
Impedance Spectroscopy Materials, (Model-) Electrodes and Single Cells
IWEslide: 5, 9/17/2009source: 2009-06-24 EIS Diagnosis for Stacks.ppt,
Universität Karlsruhe (TH)Institut für Werkstoffe der Elektrotechnik
Electrochemical Impedance Spectroscopy
H. Gerischer, Elektrodenpolarisation bei Überlagerung von Wechselstrom und Gleichstrom. Z. Elektrochem., 58, 9, 278, 1954
Analysis of Solid Electrolytes by Impedance Spectroscopy
J. E. Bauerle, Study of solid electrolyte polarization by a complex admittance method, J. Phys. Chem. Solids 30, 2657, 1969
see above
Impedance Spectroscopy Materials, (Model-) Electrodes and Single Cells
Analysis of Electrode Microstructure and Degradation Behaviour
T. Kawada, N. Sakai, H. Yokokawa, M. DokiyaM. Dokiya, M. Mori, T. Iwata, Characteristics of Slurry-Coated Nickel Zirconia Cermet Anodes for Solid Oxide Fuel Cells, J. Electro-chem. Soc., 137, 3042, 1990
IWEslide: 6, 9/17/2009source: 2009-06-24 EIS Diagnosis for Stacks.ppt,
Universität Karlsruhe (TH)Institut für Werkstoffe der Elektrotechnik
Impedance Spectrum of an Anode Supported Single Cell
IWE
0.20 0.25 0.30 0.35 0.40 0.45 0.50 0.55 0.600.00
-0.05
-0.10
-0.15
-0.20
-0.25
cell type: ASCel. area: 1 cm²fuel: H2 (9.4% H2O), 250 sccmoxidant: air, 250 sccm
Z‘‘/
Ω⋅c
m²
Z‘ / Ω⋅cm²100 101 102 103 104 105
0.00
0.01
0.02
0.03
0.04
0.05
0.06
0.07
0.08
f / Hz
spectrum: -Z´´(f)
-Z‘‘
/ Ω⋅c
m²
• 2 or more electrochemical processes ???• high resolution impedance data analysis required !!!
anode supported single cell (Forschungszentrum Jülich)Ni-8YSZ substrate (50x50x1mm³)Ni-8YSZ anode functional layer8YSZ electrolyte (~ 10 µm)CGO interlayer (~ 7 µm)LSCF cathode (10x10mm²)
IWEslide: 7, 9/17/2009source: 2009-06-24 EIS Diagnosis for Stacks.ppt,
Universität Karlsruhe (TH)Institut für Werkstoffe der Elektrotechnik
R1 R2
C2C1
γ
τ
⎟⎟⎠
⎞⎜⎜⎝
⎛
gesRR1 ⎟
⎟⎠
⎞⎜⎜⎝
⎛
gesRR2
τ1 τ2
ideal:
pol pol0
( )Z ( ) R d1 j
∞ γ τω = τ
+ ωτ∫ γ(τ): „Distribution function ofrelaxation times“
Process 1(RQ/CPE)
Process 2(RQ/CPE)
real:
γ
ττ1 τ2
Impedance Data AnalysisDistribution of Relaxation Times (DRT)
IWE
H. Schichlein et al., Deconvolution of Electrochemical Impedance Spectra for the Identification of Electrode Reaction Mechanisms in Solid Oxide Fuel Cells, J. Appl. Electrochemistry, 32, 8, 875, (2002)
IWEslide: 8, 9/17/2009source: 2009-06-24 EIS Diagnosis for Stacks.ppt,
Universität Karlsruhe (TH)Institut für Werkstoffe der Elektrotechnik
Impedance Spectrum of an Anode Supported Single CellDistribution of Relaxation Times
IWE
0.20 0.25 0.30 0.35 0.40 0.45 0.50 0.55 0.600.00
-0.05
-0.10
-0.15
-0.20
-0.25
cell type: ASCel. area: 1 cm²fuel: H2 (9.4% H2O), 250 sccmoxidant: air, 250 sccm
Z‘‘/
Ω⋅c
m²
Z‘ / Ω⋅cm²100 101 102 103 104 105
0.00
0.01
0.02
0.03
0.04
0.05
0.06
0.07
0.08
f / Hz
spectrum: -Z´´(f)DRT: g(f)
-Z‘‘
/ Ω⋅c
m²,
g(f)
/ Ω
⋅sec
• high resolution data analysis by the DRT• 5 processes resovable
→ perform impedance measurements at varying operating conditions !A. Leonide et al., J. Electrochem. Soc, 155 (1), pp. B36-B41, (2008).
IWEslide: 9, 9/17/2009source: 2009-06-24 EIS Diagnosis for Stacks.ppt,
Universität Karlsruhe (TH)Institut für Werkstoffe der Elektrotechnik
Analysis of Electrochemical Processes in an ASCVariation of Operating Temperature
IWE
1 10 1000.00
0.01
0.02
0.03
0.04
0.05
g(f)
/ Ohm
*sec
f / Hz
730740750770800860
T / °C
T = 600 ... 850 °Cfuel: H2, 250 sccmp(H2O) = 0.635 barox.: air, 250 sccm
• up to 5 different electrochemical processes resolvable• impedance values in between 10 and 1000 mΩ⋅cm²
P3A
P2AP2C
P1A
103 104 105 0.9 1.0 1.1
0.01
0.1
1
850 800 750 700 650 600
ASR
/ Ω
⋅cm
²1000 K/T
temperature/°C
R2A+R3A: anode electrochemistry
R1A: gas diffusion R2C: cathode electrochemistry
Ea,2A+3A=1.30 eV
Ea,2C=1.43 eV
A. Leonide et al., J. Electrochem. Soc, 155 (1), pp. B36-B41, (2008).
IWEslide: 10, 9/17/2009source: 2009-06-24 EIS Diagnosis for Stacks.ppt,
Universität Karlsruhe (TH)Institut für Werkstoffe der Elektrotechnik
Analysis of Electrochemical Processes in an ASCImpedance Model of a Single Cell
IWE
cell type: ASCel. area: 1 cm²fuel: H2 (9.4% H2O), 250 sccmoxidant: air, 250 sccmT = 717 °COCV
impedance spectrum
anodiccathodic
oxygen surface exchange kinetics and O2--diffusivity
p(O2), T10...500 Hz, 8...50 mΩcm2P2C
p(H2), p(H2O), T12...25 kHz,10...130 mΩcm2P3A
gas diffusion coupled with charge transfer reaction and ionic transport (AFL: anode functional layer)
p(H2), p(H2O),T2...8 kHz, 10...50 mΩcm2P2A
gas diffusion (anode substrate)p(H2), p(H2O)4...20 Hz, 30...150 mΩcm2P1A
gas diffusion (<< 10 mΩ⋅cm² in air)p(O2)0.3...10 Hz, 2...100 mΩcm2P1C
electrode process / physical origindependencefr , ASRAbbreviation
0.0 0.1 0.2 0.3 0.4 0.5 0.60.0
-0.1
-0.2
Z‘‘/
Ω⋅c
m2
Z‘ / Ω⋅cm2
CPE2 CPE3 CPE1
R3A R2A R2C R1A R1C
Q3A Q2A Q1C
R0
CNLS-Fit0( )G
ZZk j
ω =+ ω
( )tanh ( )
( )W W
j TZ R
j T
α
α
ωω
ω
⎡ ⎤⎣ ⎦= ⋅
0
1( )( )nQ
j Yω
ω=
P3AP2A P2C P1A
A. Leonide et al., J. Electrochem. Soc, 155 (1), pp. B36-B41, (2008).
IWEslide: 11, 9/17/2009source: 2009-06-24 EIS Diagnosis for Stacks.ppt,
Universität Karlsruhe (TH)Institut für Werkstoffe der Elektrotechnik
IWE
Electrochemical Impedance Spectroscopy for StacksImpact of Cell and Stack Size
anode supported single cell1 cm² active electrode area
ASR: 0.08 ... 2 Ω⋅cm²→ 80 mΩ ... 2 Ω
single cell 100 cm² → 0.8 ... 20 mΩ
• impedance of a few mΩ per cell• gradients in temperature, gas
composition etc.• gas conversion impedance• additional noise and error sources
IWEslide: 12, 9/17/2009source: 2009-06-24 EIS Diagnosis for Stacks.ppt,
Universität Karlsruhe (TH)Institut für Werkstoffe der Elektrotechnik
Electrochemical Impedance Spectroscopy for StacksTesting Equipment
websites and datasheets of manufacturers
3001020± 5 / 10 / 2050100max. bias voltage[V]
10005020± 40 / 20 / 10 25100max. bias current [A]
1500.5n.s.0.250.1253max. power diss. [kW]
1 % / 1°2 % / 2°n.s.0.25 % (f, |Z| not specified)
30 % / 30°(@ 10 mΩ)
1 %accuracy (error at 1 mΩ / 100 kHz)
0.1 mΩ ... 15 Ω
n.s.n.s.1 µΩ ... 1 kΩ10 µΩ ... 1 kΩ0.1 ... 100 mΩ
impedance range
200 µHz ... 100 kHz
10 µHz ... 10 kHz
(10 µHz ... 1 MHz)
10 µHz ... 200 kHz
10 µHz ... 100 kHz
1 mHz ... 1 MHz
frequency range
TrueData-EISCLB 500VersaSTAT4 + Power Booster
IM6 + PP 2xx1260/1287 + Power Booster
target values
3 kWel SOFC stack60 cells a 100 cm²Ustack = 42 VIstack = 71.4 A
→ limitations due to the testing equipment
IWEslide: 13, 9/17/2009source: 2009-06-24 EIS Diagnosis for Stacks.ppt,
Universität Karlsruhe (TH)Institut für Werkstoffe der Elektrotechnik
Analysis of Electrochemical Processes in an ASCGas Conversion Impedance (at decreased fuel flow rate)
IWE, A. Leonide, presented at European SOFC Forum, Lucerne 2008
0.01
0.02
0.03
0.04250 ml/min
150 ml/min100 ml/min
50 ml/min
g(f)/
Ωs
00.01 0.1 1 10 100 1000 10k 100k 1M
f/Hz
anodecathode(+ 2nd peak ofanode gas diffusion)
gas diffusion(anode substrate)
gasconversion(gas channel)
→ the gas conversion impedance will be included in the stack impedance
IWEslide: 14, 9/17/2009source: 2009-06-24 EIS Diagnosis for Stacks.ppt,
Universität Karlsruhe (TH)Institut für Werkstoffe der Elektrotechnik
IWE
Electrochemical Impedance Spectroscopy for Stacks2-dimensional Impedance Model
...
...
...
...
...
...
R2A(x)
R1A(x)
R1C(x)
U
R2C(x)
R0(x)
P3A(x)
H2+ 20% H2O H2+ 80% H2O
oxidant (air)
fuel
electrolytecathode
anode
1 A. Leonide et al., J. Electrochem. Soc, 155 (1), pp. B36-B41, (2008).
• based on the impedance model of a single cell1
• single cell impedance units along a gas channel
• impact of the gas utilization on the local impedance is considered
• dynamics of gas conversion have to be taken into account
D. Klotz et al., accepted for publication in ECS Transactions (2009)
IWEslide: 15, 9/17/2009source: 2009-06-24 EIS Diagnosis for Stacks.ppt,
Universität Karlsruhe (TH)Institut für Werkstoffe der Elektrotechnik
2-dimensional Impedance ModelLocal Impedance Spectra and Stack Impedance
Ucell = 750 mV
simulated fuel utilization along the gas channel
simulated local impedance spectra and impedance spectrum of the stack
D. Klotz et al., accepted for publication in ECS Transactions (2009)
IWE
IWEslide: 16, 9/17/2009source: 2009-06-24 EIS Diagnosis for Stacks.ppt,
Universität Karlsruhe (TH)Institut für Werkstoffe der Elektrotechnik
2-dimensional Impedance Model for StacksSpace and Time Dependence of the Fuel Utilization βf
operating parameters
Ucell 0,725 V
Uampl. 70 mV
fAC 50 Hz
L 10 cm
vgas 3 m/s
βf,in 20%
βf,out 80%
t [s]time / ms
IWE
IWEslide: 17, 9/17/2009source: 2009-06-24 EIS Diagnosis for Stacks.ppt,
Universität Karlsruhe (TH)Institut für Werkstoffe der Elektrotechnik
IWE, presented at Solid State Ionics 15 (2005)
ExperimentalSulzer Hexis Stack Test Bench
Sulzer Hexis stack test bench• 5 cell stack• 100 cm² electrode area• operating on pipeline gas• desulfurization (disengageable)• catalytic partial oxidation• controlled gas flows• controlled stack temperature
(not thermal self-sustaining)• variable interconnect /
flow field geometry• testing of different MEAs and
MICs possible
Impedance spectroscopy ?
IWEslide: 18, 9/17/2009source: 2009-06-24 EIS Diagnosis for Stacks.ppt,
Universität Karlsruhe (TH)Institut für Werkstoffe der Elektrotechnik
IWE, presented at Solid State Ionics 15 (2005)
Sulzer Hexis Stack Test BenchModifications for Impedance Spectroscopy
EIS-Equipment• Zahner IM6 & PP200 potentiostat• impedance range: 1 µΩ ... 1 kΩ• frequency range: 10 µHz ... 100 kHz• dc current: 20 A
Significant interferences at frequencies above 10 kHz
initial state
frequenzy / kHzim
peda
nce
/ mΩ
phase / °
IWEslide: 19, 9/17/2009source: 2009-06-24 EIS Diagnosis for Stacks.ppt,
Universität Karlsruhe (TH)Institut für Werkstoffe der Elektrotechnik
IWE, presented at Solid State Ionics 15 (2005)
Sulzer Hexis Stack Test BenchModifications for Impedance Spectroscopy
Modifications• adaptation of voltage probes & current lines to
decrease mutual inductances• impedance converters for dc voltage metering• multiplexer for single cell / stack impedance
measurement
Low interferences over the whole frequency range
modified
frequenzy / kHzim
peda
nce
/ mΩ
phase / °
IWEslide: 20, 9/17/2009source: 2009-06-24 EIS Diagnosis for Stacks.ppt,
Universität Karlsruhe (TH)Institut für Werkstoffe der Elektrotechnik
IWE, presented at Solid State Ionics 15 (2005)
Stack DiagnosisImpedance Spectra of Stacks and Cell Units
0.06
0.04
0.02
00 0.02 0.04 0.06 0.08 0.1 0.12
Z´/ Ohm
-Z´´
/ Ohm
Stack A: Sulzer Hexis MEAs & MICs 2002
5 cell stackelectrode area: 100 cm²oxidant: air, 1000 g/htemperature: 930 °Cfuel: natural gas, 20 g/hfuel processing:CPO, λPOx: 0.28
Stack-0.03
-0.02
-0.01
00 0.01 0.02 0.03 0.04 0.05
Z´/ Ohm
Z´´/
Ohm
cell 1cell 2cell 3cell 4cell 5
Stack A
0 0.01 0.02 0.03 0.04 0.05Z´/ Ohm
-0.03
-0.02
-0.01
0Z´
´/ O
hm
Stack B cell 1cell 2cell 3cell 4cell 5
Single Cell Units 1 to 5
Impedance spectra of the stack provide an averaged ohmic and polarisation resistanceImpedance spectra of the individual cell units provide more detailed information
Stack B: Sulzer Hexis MEAs & MICs 2004
IWEslide: 21, 9/17/2009source: 2009-06-24 EIS Diagnosis for Stacks.ppt,
Universität Karlsruhe (TH)Institut für Werkstoffe der Elektrotechnik
System DiagnosisImpedance Data Analysis by parametric extended DRT
IWE, presented at Solid State Ionics 15 (2005)
-0.01
00.015 0.02 0.025 0.03 0.035
Re Z / Ω
ImZ
/ Ω 12 mHz10 Hz
100 kHz
impedance spectra
τ
γ(τ)
Z(DRT)
τRQ , nRQ, RRQ
RQ - element
LL RL
Series resistanceinductance
0
0.002
0.004
0.006
-2 0 2 4log(1s/τ)
γ(τ)
/ Ω
⋅s
gas conversionimpedance
DRT
IWEslide: 22, 9/17/2009source: 2009-06-24 EIS Diagnosis for Stacks.ppt,
Universität Karlsruhe (TH)Institut für Werkstoffe der Elektrotechnik
IWE, presented at Solid State Ionics 15 (2005)
System DiagnosisImpact of CPOx Reformer Temperature on cell voltage and nRQ
0.86
0.87
0.88
0.89
Tpox / °C
U /
V
Cell 1
0.9
0.905
0.91
0.915
0.92
0.925
575 625 675 725
n CPE
Tpox / °C
no dependency in cell voltage
Variation in fuel composition is detected
theory: n 1 for pure H2
RQ exponent nRQ
voltage cell 1
575 625 675 725
IWEslide: 23, 9/17/2009source: 2009-06-24 EIS Diagnosis for Stacks.ppt,
Universität Karlsruhe (TH)Institut für Werkstoffe der Elektrotechnik
IWE
Conclusions and OutlookFuture Research Activities - Diagnostic Tools for FC-Technologies
• Impedance spectroscopy is a powerful tool to analyze SOFC stacks but
• The available testing equipment hardly fulfills the requirements
• The stack testing facilities have to be designed for impedance spectroscopy
• Complex impedance models are required to understand the stack impedance
• To do´s:
• Development of impedance analyzers for (SOFC-) stacks
• Development of tools for stack impedance modeling and data analysis
• Standardized testing procedures for stack impedance measurement and data analysis
IWEslide: 24, 9/17/2009source: 2009-06-24 EIS Diagnosis for Stacks.ppt,
Universität Karlsruhe (TH)Institut für Werkstoffe der Elektrotechnik
Impedance Spectroscopy and Impedance Data AnalysisIWE-References
IWE
• H. Schichlein, M. Feuerstein, A. C. Müller, A. Weber, A. Krügel and E. Ivers-Tiffée, "System identification: a new modelling approach for SOFC single cells", Proceedings of the Sixth International Symposium on Solid Oxide Fuel Cells (SOFC-VI), pp. 1069-1077 (1999).
• H. Schichlein, Experimentelle Modellbildung für die Hochtemperatur-Brennstoffzelle SOFC, Aachen: Verlag Mainz (2003).
• E. Ivers-Tiffée, A. Weber and H. Schichlein, "Electrochemical impedance spectroscopy", in W. Vielstich, H. A. Gasteiger, and A. Lamm (Eds.), Handbook of Fuel Cells - Fundamentals, Technology and Applications, Chichester: John Wiley & Sons Ltd, pp. 220-235 (2003).
• E. Ivers-Tiffée, A. Weber and H. Schichlein, "O2-reduction at high temperatures: SOFC", in W. Vielstich, H. A. Gasteiger, and A. Lamm (Eds.), Handbook of Fuel Cells - Fundamentals, Technology and Applications, Chichester: John Wiley & Sons Ltd, pp. 587-600 (2003).
• H. Schichlein, A. C. Müller, M. Voigts, A. Krügel and E. Ivers-Tiffée, "Deconvolution of electrochemical impedance spectra for the identification of electrode reaction mechanisms in solid oxide fuel cells", Journal of Applied Electrochemistry 32, pp. 875-882 (2002).
• V. Sonn, A. Leonide and E. Ivers-Tiffée, "Towards Understanding the Impedance Response of Ni/YSZ Anodes", ECS Transactions 7, pp. 1363-1372 (2007).
• A. Leonide, V. Sonn, A. Weber and E. Ivers-Tiffée, "Evaluation and Modelling of the Cell Resistance in Anode Supported Solid Oxide Fuel Cells", ECS Transactions 7, pp. 521-531 (2007).
• A. Leonide, V. Sonn, A. Weber and E. Ivers-Tiffée, "Evaluation and modeling of the cell resistance in anode-supported solid oxide fuel cells", J. Electrochem. Soc. 155, p. B36-B41 (2008).
IWEslide: 25, 9/17/2009source: 2009-06-24 EIS Diagnosis for Stacks.ppt,
Universität Karlsruhe (TH)Institut für Werkstoffe der Elektrotechnik
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