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International Symposium on Diagnostics Tools for Fuel Cell Technologies Impedance Spectroscopy as a Diagnosis Tool for SOFC Stacks and Systems Andr Weber, Dino Klotz, Volker Sonn, Ellen Ivers-Tiffe Institut fr Werkstoffe der

  1. 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 IWE Universität Karlsruhe (TH) Institut für Werkstoffe der Elektrotechnik source: IWE 2009-06-24 EIS Diagnosis for Stacks.ppt, slide: 1, 9/17/2009

  2. 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 • stack performance and efficiency • stack performance and efficiency • stack temperature(s) • stack temperature(s) • reformer temperature(s) • reformer temperature(s) • steam to carbon ratio / λ POx -value • actual steam to carbon ratio / λ POx -value • fuel (reformate) composition • fuel (reformate) composition • oxidant and fuel flow rates • oxidant and fuel flow rates • oxidant and fuel temperatures at gas inlet • oxidant and fuel temperatures at gas inlet • oxidant and fuel pressure inlet • oxidant and fuel pressures at gas inlet • exhaust gas composition (remaining CO, HC´s) • exhaust gas composition (remaining CO, HC´s) • ... • ... Monitoring of the internal resistance of the stack by electrochemical impedance spectroscopy IWE Universität Karlsruhe (TH) Institut für Werkstoffe der Elektrotechnik source: ENBW, Delphi 2009-06-24 EIS Diagnosis for Stacks.ppt, slide: 2, 9/17/2009

  3. Impedance Spectroscopy Materials, (Model-) Electrodes and Single Cells Electrochemical Impedance Spectroscopy H. Gerischer, Elektrodenpolarisation bei Überlagerung von Wechselstrom und Gleichstrom. Z. Elektrochem., 58 , 9, 278, 1954 IWE Universität Karlsruhe (TH) Institut für Werkstoffe der Elektrotechnik source: see above 2009-06-24 EIS Diagnosis for Stacks.ppt, slide: 3, 9/17/2009

  4. Impedance Spectroscopy Materials, (Model-) Electrodes and Single Cells Electrochemical Impedance Spectroscopy Analysis of Solid Electrolytes by Impedance Spectroscopy H. Gerischer, Elektrodenpolarisation bei Überlagerung von Wechselstrom und Gleichstrom. Z. Elektrochem., 58 , 9, 278, 1954 J. E. Bauerle, Study of solid electrolyte polarization by a complex admittance method, J. Phys. Chem. Solids 30 , 2657, 1969 IWE Universität Karlsruhe (TH) Institut für Werkstoffe der Elektrotechnik source: see above 2009-06-24 EIS Diagnosis for Stacks.ppt, slide: 4, 9/17/2009

  5. Impedance Spectroscopy Materials, (Model-) Electrodes and Single Cells Electrochemical Impedance Spectroscopy Analysis of Solid Electrolytes by Impedance Spectroscopy Analysis of Electrode Microstructure and Degradation Behaviour T. Kawada, N. Sakai, H. Yokokawa, M. Dokiya, M. Mori, T. Iwata, M. Dokiya Characteristics of Slurry-Coated Nickel Zirconia Cermet Anodes for Solid Oxide Fuel Cells , J. Electro- chem. Soc., 137 , 3042, 1990 H. Gerischer, Elektrodenpolarisation bei Überlagerung von Wechselstrom und Gleichstrom. Z. Elektrochem., 58 , 9, 278, 1954 J. E. Bauerle, Study of solid electrolyte polarization by a complex admittance method, J. Phys. Chem. Solids 30 , 2657, 1969 IWE Universität Karlsruhe (TH) Institut für Werkstoffe der Elektrotechnik source: see above 2009-06-24 EIS Diagnosis for Stacks.ppt, slide: 5, 9/17/2009

  6. Impedance Spectrum of an Anode Supported Single Cell anode supported single cell (Forschungszentrum Jülich) Ni-8YSZ substrate (50x50x1mm³) 0.08 Ni-8YSZ anode functional layer -0.25 8YSZ electrolyte (~ 10 µm) spectrum: -Z´´(f) 0.07 CGO interlayer (~ 7 µm) LSCF cathode (10x10mm²) -0.20 0.06 - Z‘‘ / Ω⋅ cm² 0.05 Z‘‘ / Ω⋅ cm² -0.15 0.04 -0.10 0.03 0.02 -0.05 0.01 0.00 0.00 0.20 0.25 0.30 0.35 0.40 0.45 0.50 0.55 0.60 0 1 2 3 4 5 10 10 10 10 10 10 Z‘ / Ω⋅ cm² f / Hz • 2 or more electrochemical processes ??? cell type: ASC • high resolution impedance data analysis required !!! el. area: 1 cm² fuel: H 2 (9.4% H 2 O), 250 sccm oxidant: air, 250 sccm IWE Universität Karlsruhe (TH) Institut für Werkstoffe der Elektrotechnik source: IWE 2009-06-24 EIS Diagnosis for Stacks.ppt, slide: 6, 9/17/2009

  7. Impedance Data Analysis Distribution of Relaxation Times (DRT) ⎛ ⎞ R 1 R 2 R 2 γ ⎜ ⎟ ⎛ ⎞ ⎜ ⎟ R 1 R ⎜ ⎟ ⎝ ⎠ ges ⎜ ⎟ R ⎝ ⎠ ideal: C 1 C 2 ges τ τ 1 τ 2 γ real: Process 1 Process 2 τ τ 1 τ 2 (RQ/CPE) (RQ/CPE) ∞ γ τ ( ) ∫ γ ( τ ): „Distribution function of ω = τ Z ( ) R d + ωτ pol pol 1 j relaxation times“ 0 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 Universität Karlsruhe (TH) Institut für Werkstoffe der Elektrotechnik source: IWE 2009-06-24 EIS Diagnosis for Stacks.ppt, slide: 7, 9/17/2009

  8. Impedance Spectrum of an Anode Supported Single Cell Distribution of Relaxation Times 0.08 -0.25 spectrum: -Z´´(f) 0.07 DRT: g(f) - Z‘‘ / Ω⋅ cm² , g(f) / Ω⋅ sec -0.20 0.06 0.05 Z‘‘ / Ω⋅ cm² -0.15 0.04 -0.10 0.03 0.02 -0.05 0.01 0.00 0.00 0.20 0.25 0.30 0.35 0.40 0.45 0.50 0.55 0.60 0 1 2 3 4 5 10 10 10 10 10 10 Z‘ / Ω⋅ cm² f / Hz • high resolution data analysis by the DRT cell type: ASC • 5 processes resovable el. area: 1 cm² → perform impedance measurements at varying operating conditions ! fuel: H 2 (9.4% H 2 O), 250 sccm oxidant: air, 250 sccm A. Leonide et al., J. Electrochem. Soc , 155 (1), pp. B36-B41, (2008). IWE Universität Karlsruhe (TH) Institut für Werkstoffe der Elektrotechnik source: IWE 2009-06-24 EIS Diagnosis for Stacks.ppt, slide: 8, 9/17/2009

  9. Analysis of Electrochemical Processes in an ASC Variation of Operating Temperature temperature/°C 850 800 750 700 650 600 0.05 T / °C R 2A +R 3A : anode electrochemistry 1 P 3A R 2C : cathode electrochemistry 730 0.04 R 1A : gas diffusion 740 ASR / Ω⋅ cm² 750 E a,2A+3A =1.30 eV P 2A g(f) / Ohm*sec 770 0.03 P 2C 800 860 0.1 P 1A E a,2C =1.43 eV 0.02 0.01 0.01 0.00 10 3 10 4 10 5 0.9 1.0 1.1 1 10 100 1000 K/T f / Hz • up to 5 different electrochemical processes resolvable • impedance values in between 10 and 1000 m Ω⋅ cm² T = 600 ... 850 °C fuel: H 2 , 250 sccm p(H 2 O) = 0.635 bar ox.: air, 250 sccm A. Leonide et al., J. Electrochem. Soc , 155 (1), pp. B36-B41, (2008). IWE Universität Karlsruhe (TH) Institut für Werkstoffe der Elektrotechnik source: IWE 2009-06-24 EIS Diagnosis for Stacks.ppt, slide: 9, 9/17/2009

  10. Analysis of Electrochemical Processes in an ASC Impedance Model of a Single Cell -0.2 cell type: ASC R 0 R 3A R 2A R 2C R 1A R 1C el. area: 1 cm² fuel: H 2 (9.4% H 2 O), 250 sccm CPE2 CPE3 CPE1 oxidant: air, 250 sccm Z‘‘ / Ω⋅ cm 2 1 T = 717 °C ω = Q 3A Q 2A Q 1C Q ( ) ω ) n j Y OCV ( -0.1 0 ⎡ ⎤ ω α j T tanh ( ) ⎣ ⎦ impedance spectrum ω = ⋅ Z R ( ) W ( ) W α ω CNLS-Fit j T P 3A Z anodic ω = Z P 2A 0 ( ) P 2C P 1A G + ω k j cathodic 0.0 Z‘ / Ω⋅ cm 2 0.0 0.1 0.2 0.3 0.4 0.5 0.6 Abbreviation f r , ASR dependence electrode process / physical origin 0.3...10 Hz, 2...100 m Ω cm 2 gas diffusion (<< 10 m Ω⋅ cm² in air) P 1C p(O 2 ) 10...500 Hz, 8...50 m Ω cm 2 P 2C p(O 2 ), T oxygen surface exchange kinetics and O 2- - diffusivity 4...20 Hz, 30...150 m Ω cm 2 P 1A p(H 2 ), p(H 2 O) gas diffusion (anode substrate) 2...8 kHz, 10...50 m Ω cm 2 P 2A p(H 2 ), p(H 2 O),T gas diffusion coupled with charge transfer reaction and ionic transport (AFL: anode 12...25 kHz,10...130 m Ω cm 2 P 3A p(H 2 ), p(H 2 O), T functional layer) A. Leonide et al., J. Electrochem. Soc , 155 (1), pp. B36-B41, (2008). IWE Universität Karlsruhe (TH) Institut für Werkstoffe der Elektrotechnik source: IWE 2009-06-24 EIS Diagnosis for Stacks.ppt, slide: 10, 9/17/2009

  11. Electrochemical Impedance Spectroscopy for Stacks Impact of Cell and Stack Size anode supported single cell single cell → 0.8 ... 20 m Ω 1 cm² active electrode area 100 cm² • impedance of a few m Ω per cell • gradients in temperature, gas composition etc. • gas conversion impedance ASR: 0.08 ... 2 Ω⋅ cm² → 80 m Ω ... 2 Ω • additional noise and error sources IWE Universität Karlsruhe (TH) Institut für Werkstoffe der Elektrotechnik source: IWE 2009-06-24 EIS Diagnosis for Stacks.ppt, slide: 11, 9/17/2009

  12. Electrochemical Impedance Spectroscopy for Stacks Testing Equipment 3 kW el SOFC stack 60 cells a 100 cm² U stack = 42 V target 1260/1287 + IM6 + PP 2xx VersaSTAT4 + CLB 500 TrueData-EIS values Power Booster Power Booster I stack = 71.4 A frequency range 1 mHz ... 10 µHz ... 100 10 µHz ... (10 µHz ... 1 10 µHz ... 10 200 µHz ... 1 MHz kHz 200 kHz MHz) kHz 100 kHz 10 µ Ω ... 1 k Ω 1 µ Ω ... 1 k Ω 0.1 m Ω ... 15 impedance range 0.1 ... n.s. n.s. 100 m Ω Ω accuracy (error at 1 1 % 30 % / 30° 0.25 % (f, |Z| n.s. 2 % / 2° 1 % / 1° m Ω / 100 kHz) (@ 10 m Ω ) not specified) ± 5 / 10 / 20 max. bias voltage 100 50 20 10 300 [V] ± 40 / 20 / 10 max. bias current 100 25 20 50 1000 [A] max. power diss. 3 0.125 0.25 n.s. 0.5 150 [kW] → limitations due to the testing equipment IWE Universität Karlsruhe (TH) Institut für Werkstoffe der Elektrotechnik source: websites and datasheets of manufacturers 2009-06-24 EIS Diagnosis for Stacks.ppt, slide: 12, 9/17/2009

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