IWE Universitt Karlsruhe (TH) Institut fr Werkstoffe der - - PowerPoint PPT Presentation

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slide: 1, 9/17/2009 source: 2009-06-24 EIS Diagnosis for Stacks.ppt,

Universität Karlsruhe (TH) Institut für Werkstoffe der Elektrotechnik International Symposium on Diagnostics 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

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IWE

slide: 2, 9/17/2009 source: 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 Systems Stack 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)
• ...

IWE

slide: 3, 9/17/2009 source: 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

IWE

slide: 4, 9/17/2009 source: 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

IWE

slide: 5, 9/17/2009 source: 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. Dokiya
• M. 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

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slide: 6, 9/17/2009 source: 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 0.60 0.00

• 0.05
• 0.10
• 0.15
• 0.20
• 0.25

cell type: ASC

• el. area: 1 cm²

fuel: H2 (9.4% H2O), 250 sccm

• xidant: air, 250 sccm

Z‘‘ / Ω⋅cm² Z‘ / Ω⋅cm²

10 10

1

10

2

10

3

10

4

10

5

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⋅cm²
• 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 layer 8YSZ electrolyte (~ 10 µm) CGO interlayer (~ 7 µm) LSCF cathode (10x10mm²)

IWE

slide: 7, 9/17/2009 source: 2009-06-24 EIS Diagnosis for Stacks.ppt,

Universität Karlsruhe (TH) Institut für Werkstoffe der Elektrotechnik

R1 R2 C2 C1

γ τ

⎟ ⎟ ⎠ ⎞ ⎜ ⎜ ⎝ ⎛

ges

R R1

⎟ ⎟ ⎠ ⎞ ⎜ ⎜ ⎝ ⎛

ges

R R2

τ1 τ2

ideal:

pol pol

( ) Z ( ) R d 1 j

∞

γ τ ω = τ + ωτ

∫

γ(τ): „Distribution function of

relaxation times“ Process 1 (RQ/CPE) Process 2 (RQ/CPE) real:

γ τ τ1 τ2

Impedance Data Analysis Distribution 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)

IWE

slide: 8, 9/17/2009 source: 2009-06-24 EIS Diagnosis for Stacks.ppt,

Universität Karlsruhe (TH) Institut für Werkstoffe der Elektrotechnik

Impedance Spectrum of an Anode Supported Single Cell Distribution of Relaxation Times

IWE

0.20 0.25 0.30 0.35 0.40 0.45 0.50 0.55 0.60 0.00

• 0.05
• 0.10
• 0.15
• 0.20
• 0.25

cell type: ASC

• el. area: 1 cm²

fuel: H2 (9.4% H2O), 250 sccm

• xidant: air, 250 sccm

Z‘‘ / Ω⋅cm² Z‘ / Ω⋅cm²

10 10

1

10

2

10

3

10

4

10

5

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⋅cm² , 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).

IWE

slide: 9, 9/17/2009 source: 2009-06-24 EIS Diagnosis for Stacks.ppt,

Universität Karlsruhe (TH) Institut für Werkstoffe der Elektrotechnik

Analysis of Electrochemical Processes in an ASC Variation of Operating Temperature

IWE

1 10 100 0.00 0.01 0.02 0.03 0.04 0.05

g(f) / Ohm*sec

f / Hz 730 740 750 770 800 860

T / °C

T = 600 ... 850 °C fuel: H2, 250 sccm p(H2O) = 0.635 bar

• x.: air, 250 sccm
• up to 5 different electrochemical processes resolvable
• impedance values in between 10 and 1000 mΩ⋅cm²

P3A P2A P2C P1A

103 104 105 0.9 1.0 1.1 0.01 0.1 1 850 800 750 700 650 600 ASR / Ω⋅cm² 1000 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).

IWE

slide: 10, 9/17/2009 source: 2009-06-24 EIS Diagnosis for Stacks.ppt,

Universität Karlsruhe (TH) Institut für Werkstoffe der Elektrotechnik

Analysis of Electrochemical Processes in an ASC Impedance Model of a Single Cell

IWE

cell type: ASC

• el. area: 1 cm²

fuel: H2 (9.4% H2O), 250 sccm

• xidant: air, 250 sccm

T = 717 °C OCV

impedance spectrum anodic cathodic

• xygen surface exchange kinetics and O2--

diffusivity p(O2), T 10...500 Hz, 8...50 mΩcm2 P2C p(H2), p(H2O), T 12...25 kHz,10...130 mΩcm2 P3A gas diffusion coupled with charge transfer reaction and ionic transport (AFL: anode functional layer) p(H2), p(H2O),T 2...8 kHz, 10...50 mΩcm2 P2A gas diffusion (anode substrate) p(H2), p(H2O) 4...20 Hz, 30...150 mΩcm2 P1A gas diffusion (<< 10 mΩ⋅cm² in air) p(O2) 0.3...10 Hz, 2...100 mΩcm2 P1C

electrode process / physical origin dependence fr , ASR

Abbreviation

0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.0

• 0.1
• 0.2

Z‘‘ / Ω⋅cm2 Z‘ / Ω⋅cm2

CPE2 CPE3 CPE1

R3A R2A R2C R1A R1C Q3A Q2A Q1C R0 CNLS-Fit ( )

G

Z Z k j ω = + ω

( )

tanh ( ) ( )

W W

j T Z R j T

α α

ω ω ω ⎡ ⎤ ⎣ ⎦ = ⋅ 1 ( ) ( )n Q j Y ω ω = P3A P2A P2C P1A

• A. Leonide et al., J. Electrochem. Soc, 155 (1), pp. B36-B41, (2008).

IWE

slide: 11, 9/17/2009 source: 2009-06-24 EIS Diagnosis for Stacks.ppt,

Universität Karlsruhe (TH) Institut für Werkstoffe der Elektrotechnik

IWE

Electrochemical Impedance Spectroscopy for Stacks Impact of Cell and Stack Size

anode supported single cell 1 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

IWE

slide: 12, 9/17/2009 source: 2009-06-24 EIS Diagnosis for Stacks.ppt,

Universität Karlsruhe (TH) Institut für Werkstoffe der Elektrotechnik

Electrochemical Impedance Spectroscopy for Stacks Testing Equipment

websites and datasheets of manufacturers

300 10 20 ± 5 / 10 / 20 50 100

• max. bias voltage

[V] 1000 50 20 ± 40 / 20 / 10 25 100

• max. bias current

[A] 150 0.5 n.s. 0.25 0.125 3

• max. 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 kΩ 10 µΩ ... 1 kΩ 0.1 ... 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-EIS CLB 500 VersaSTAT4 + Power Booster IM6 + PP 2xx 1260/1287 + Power Booster target values 3 kWel SOFC stack 60 cells a 100 cm² Ustack = 42 V Istack = 71.4 A

→ limitations due to the testing equipment

IWE

slide: 13, 9/17/2009 source: 2009-06-24 EIS Diagnosis for Stacks.ppt,

Universität Karlsruhe (TH) Institut für Werkstoffe der Elektrotechnik

Analysis of Electrochemical Processes in an ASC Gas Conversion Impedance (at decreased fuel flow rate)

IWE, A. Leonide, presented at European SOFC Forum, Lucerne 2008

0.01 0.02 0.03 0.04

250 ml/min 150 ml/min 100 ml/min 50 ml/min g(f)/Ωs

0.01 0.1 1 10 100 1000 10k 100k 1M

f/Hz

anode cathode

(+ 2nd peak of anode gas diffusion)

gas diffusion

(anode substrate)

gas conversion

(gas channel)

→ the gas conversion impedance will be included in the stack impedance

IWE

slide: 14, 9/17/2009 source: 2009-06-24 EIS Diagnosis for Stacks.ppt,

Universität Karlsruhe (TH) Institut für Werkstoffe der Elektrotechnik

IWE

Electrochemical Impedance Spectroscopy for Stacks 2-dimensional Impedance Model

... ... ... ... ... ...

R2A(x) R1A(x) R1C(x) U R2C(x) R0(x) P3A(x)

H2+ 20% H2O H2+ 80% H2O

• xidant (air)

fuel electrolyte cathode anode

1 A. Leonide et al., J. Electrochem. Soc, 155 (1), pp. B36-B41, (2008).

• based on the impedance model
• f 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)

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slide: 15, 9/17/2009 source: 2009-06-24 EIS Diagnosis for Stacks.ppt,

Universität Karlsruhe (TH) Institut für Werkstoffe der Elektrotechnik

2-dimensional Impedance Model Local 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

IWE

slide: 16, 9/17/2009 source: 2009-06-24 EIS Diagnosis for Stacks.ppt,

Universität Karlsruhe (TH) Institut für Werkstoffe der Elektrotechnik

2-dimensional Impedance Model for Stacks Space and Time Dependence of the Fuel Utilization βf

• perating

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

IWE

slide: 17, 9/17/2009 source: 2009-06-24 EIS Diagnosis for Stacks.ppt,

Universität Karlsruhe (TH) Institut für Werkstoffe der Elektrotechnik

IWE, presented at Solid State Ionics 15 (2005)

Experimental Sulzer 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 ?

IWE

slide: 18, 9/17/2009 source: 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 Bench Modifications 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 / kHz impedance / mΩ phase / °

IWE

slide: 19, 9/17/2009 source: 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 Bench Modifications 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 / kHz impedance / mΩ phase / °

IWE

slide: 20, 9/17/2009 source: 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 Diagnosis Impedance Spectra of Stacks and Cell Units

0.06 0.04 0.02 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 stack electrode area: 100 cm²

• xidant: air, 1000 g/h

temperature: 930 °C fuel: natural gas, 20 g/h fuel processing: CPO, λPOx: 0.28

Stack

• 0.03
• 0.02
• 0.01

0.01 0.02 0.03 0.04 0.05 Z´/ Ohm Z´´ / Ohm cell 1 cell 2 cell 3 cell 4 cell 5

Stack A

0.01 0.02 0.03 0.04 0.05 Z´/ Ohm

• 0.03
• 0.02
• 0.01

Z´´ / Ohm

Stack B

cell 1 cell 2 cell 3 cell 4 cell 5

Single Cell Units 1 to 5 Impedance spectra of the stack provide an averaged ohmic and polarisation resistance Impedance spectra of the individual cell units provide more detailed information

Stack B: Sulzer Hexis MEAs & MICs 2004

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slide: 21, 9/17/2009 source: 2009-06-24 EIS Diagnosis for Stacks.ppt,

Universität Karlsruhe (TH) Institut für Werkstoffe der Elektrotechnik

System Diagnosis Impedance Data Analysis by parametric extended DRT

IWE, presented at Solid State Ionics 15 (2005)

• 0.01

0.015 0.02 0.025 0.03 0.035 Re Z / Ω Im Z / Ω 12 mHz 10 Hz 100 kHz

impedance spectra

τ γ(τ)

Z(DRT) τRQ , nRQ, RRQ RQ - element LL RL Series resistance inductance

0.002 0.004 0.006

• 2

2 4 log(1s/τ) γ(τ) / Ω⋅s

gas conversion impedance DRT

IWE

slide: 22, 9/17/2009 source: 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 Diagnosis Impact 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 nCPE 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

IWE

slide: 23, 9/17/2009 source: 2009-06-24 EIS Diagnosis for Stacks.ppt,

Universität Karlsruhe (TH) Institut für Werkstoffe der Elektrotechnik

IWE

Conclusions and Outlook Future 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

IWE

slide: 24, 9/17/2009 source: 2009-06-24 EIS Diagnosis for Stacks.ppt,

Universität Karlsruhe (TH) Institut für Werkstoffe der Elektrotechnik

Impedance Spectroscopy and Impedance Data Analysis IWE-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
• xide fuel cells", J. Electrochem. Soc. 155, p. B36-B41 (2008).

IWE

slide: 25, 9/17/2009 source: 2009-06-24 EIS Diagnosis for Stacks.ppt,

Universität Karlsruhe (TH) Institut für Werkstoffe der Elektrotechnik

Acknowledgements Many Thanks to our Partners and Funding Organizations

IWE & Partners

Fraunhofer Institut für Silicatforschung

NSA