Analysis of Differences in I m pedance Spectra strategies and - - PowerPoint PPT Presentation

Analysis of Differences in I m pedance Spectra

strategies and methods

Søren Højgaard Jensen*, Tânia Ramos, Johan Hjelm, Mogens Mogensen Fuel Cells and Solid State Chemistry Division Risø National Laboratory for Sustainable Energy Technical University of Denmark *shjj@risoe.dtu.dk.

Risø DTU, Technical University of Denm ark Risø DTU, Technical University of Denm ark

Exam ple: Solid Oxide Fuel Cell

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Operating conditions: 750 °C

• 0.25 A/ cm 2

gas to LSM-electrode: O2 (10 l/ h) gas to Ni-electrode: 70% H2 O + 30 % H2 (18 l/ h) Cell area: 16 cm 2

Performance decreases during electrolysis operation

Risø DTU, Technical University of Denm ark Risø DTU, Technical University of Denm ark

I m pedance Spectra Measured During Electrolysis Operation

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Risø DTU, Technical University of Denm ark Risø DTU, Technical University of Denm ark

DRT of I m pedance Spectra Measured During Electrolysis Operation

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DRT-theory: H. Schichlein, A. C. Müller, M. Voigts, A. Krügel, and E. Ivers-Tiffée, J. Appl. Electrochem., 32, 875 2002.

Risø DTU, Technical University of Denm ark Risø DTU, Technical University of Denm ark

I m pedance Spectra Measured Before and After Electrolysis Operation at OCV

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gas to Ni-electrode: H2 with either 5% or 20% H2 O gas to LSM-electrode: air before electrolysis and O2 after electrolysis

Risø DTU, Technical University of Denm ark Risø DTU, Technical University of Denm ark

I m pedance Spectra Measured Before and After Electrolysis Operation

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Z’ is the slope Z’  is the difference between the two slopes is a Ni-electrode impedance characteristic Z’ 

Risø DTU, Technical University of Denm ark Risø DTU, Technical University of Denm ark

Ni-electrode I m pedance Characteristics

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LSM-electrode I m pedance Characteristics

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…based on gas shifts at the LSM-electrode from air to O2

Risø DTU, Technical University of Denm ark Risø DTU, Technical University of Denm ark

I m pedance Spectra Measured During Electrolysis Operation

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...too many variables in an equivalent circuit model What contribute to these impedance spectra? ...LSM-electrode, Ni-electrode, Electrolyte and Wire inductance

Risø DTU, Technical University of Denm ark Risø DTU, Technical University of Denm ark

Difference spectra ( x h – 3 h)

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ADIS Measurements here without model lines ...the spectra reflect changes in the Ni-electrode impedance ...fewer variables to model the spectra.

Risø DTU, Technical University of Denm ark Risø DTU, Technical University of Denm ark

W hich I m pedance Elem ent do Best Model the Ni-electrode I m pedance?

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 

( ) ( )

1

RQ RQ n

R Z j   

?

 

1

Ge Ge n

R Z j   

?

Risø DTU, Technical University of Denm ark Risø DTU, Technical University of Denm ark

I m pedance spectra m easured before and after electrolysis operation

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   

3

3 ( ) 03

1 1

xh h

xh h RQ xh n n xh h

R R Z j j         

Risø DTU, Technical University of Denm ark Risø DTU, Technical University of Denm ark

I m pedance spectra m easured before and after electrolysis operation

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   

3

3 0 3

1 1

xh h

Ge xh Ge h Ge xh n n xh h

R R Z j j         

Risø DTU, Technical University of Denm ark Risø DTU, Technical University of Denm ark

Conclusion

• Analysis of differences in impedance spectra before and after an
• peration period can be used to determine how much the electrodes are

affected by the operation period

• Modeling of differences in impedance spectra may reduce the number of

model variables. This can enhance the modeling accuracy

• A Gerischer impedance element model the Solid Oxide Fuel Cell Ni/ YSZ-

electrode impedance more precise than a (RQ)-element

Risø DTU, Technical University of Denm ark Risø DTU, Technical University of Denm ark

Thank you for your attention

I would like to acknowledge:

• Coleagues at Fuel Cells and Solid State Chemistry Division, Risø National

Laboratory for Sustainable Energy, Technical University of Denmark

• The Financial support from Programme Commission on Sustainable

Energy and Enviroment, The Danish Counsil for Strategic Research via the SERC Project (www.serc.dk), contract no. 2104-06-0011

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