26.03.2012 | Gemeinschaftslabors Nanomaterialien | Cahit Benel

Nanostructured thin films of La0.6Sr 0.4CoO3-δ via

spray pyrolysis for micro-SOFC application

Cahit Benel, Azad J. Darbandi, Horst Hahn

Michel Prestat, René Tölke, Anna Evans

26.03.2012 | Gemeinschaftslabors Nanomaterialien | Cahit Benel 2

Fundamentals of SOFC

Anode: H2 + O2- H2O + 2 e-

Cathode: ½ O2 + 2 e- O2-

Total: H2 + ½ O2 H2O

26.03.2012 | Gemeinschaftslabors Nanomaterialien | Cahit Benel 3

MotivationLosses in SOFC

To reduce the losses:

Making the whole cell as thin as

possible

Optimizing of electrode materials

and their properties

National Energy Technology Laboratory Fuel cell handbook. 7th ed. Morgantown, WV: U.S. Department of Energy; 2004.

26.03.2012 | Gemeinschaftslabors Nanomaterialien | Cahit Benel 4

Micro-solid oxide fuel cell - State of artCollaboration with ETH Zurich

Eva

ns, A

. et.

Al.

Jour

nal o

f Pow

er S

ourc

es 1

94 (

2009

) 11

9-12

9

µPEMFC80 °Cpure H2

µDMFC

Li-ion batteries

Ni-MH batteries

µSOFC350-550 °Chydrocarbons

Cathode

Anode

Electrolyte

Si

Goal:Nanoparticulate thin film cathode

with thickness between 200 nm and 500 nm

26.03.2012 | Gemeinschaftslabors Nanomaterialien | Cahit Benel 5

Synthesis of LSCSalt-assisted Spray Pyrolysis

La0.6Sr0.4CoO3-δ (LSC)

Furnace

T

Vacuum

pump

O2

MFC

FilterControl

valve

Ultrasonic

nebulizer

p

Carrier Gas Water based precursor

26.03.2012 | Gemeinschaftslabors Nanomaterialien | Cahit Benel 6

ResultsSalt-assisted Spray Pyrolysis

As synthesized

No reaction between NaCl and LSC phase

26.03.2012 | Gemeinschaftslabors Nanomaterialien | Cahit Benel 7

Removal of Salt

As synthesized After washing

As synthesized nanopowder washed by DI water to remove NaCl.

26.03.2012 | Gemeinschaftslabors Nanomaterialien | Cahit Benel 8

XRD

Before washing After washing

Crystallite size ≈ 7 nm

26.03.2012 | Gemeinschaftslabors Nanomaterialien | Cahit Benel 9

Electrochemical Characterization

• Symmetrical cells under OCV

•1MHz-0.1Hz

•450-650 °C with 50 °C increments

•PO2=0.01-1 atm

• Yttria stabilized zirconia (YSZ) substrates

• Ce0.8Gd0.2O1.9 (GDC) buffer layer via spin coating (950 °C for 2 h)

• LSC functional layers via spin coating (550 °C for 1 h)

•LSC•LSC-GDC (10-40 wt %) nanocomposite

LSCGDC

YSZ

LSCGDC

26.03.2012 | Gemeinschaftslabors Nanomaterialien | Cahit Benel 10

Electrochemical Characterization

26.03.2012 | Gemeinschaftslabors Nanomaterialien | Cahit Benel 11

Electrochemical CharacterizationDependence of ASR on temperture & GDC concentration

* Karageorgakis et. al., Journal of Power Sources 195 (2010) 8152-8161

26.03.2012 | Gemeinschaftslabors Nanomaterialien | Cahit Benel 12

Summary

Nanocrystalline single phase LSC via SASP

Nanoparticulate thin films of LSC and LSC-GDC (10-40%) with thicknesses between 200 and 500 nm by single step spin coating

LSC-GDC (30%) nanocomposite films showed the lowest ASR values

0.78 Ω cm2 (250 nm thickness, @ 600 °C)

Next step

To check the performance of the LSC functional thin films on free standing electrolytes

26.03.2012 | Gemeinschaftslabors Nanomaterialien | Cahit Benel 13

Financial support:

Center for Functional Nanostructures (CFN)

Equipment support:

Acknowledgments

Elektrochemie Verbund-Süd

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Thank you for your attention

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26.03.2012 | Gemeinschaftslabors Nanomaterialien | Cahit Benel 17

Free standing electrolyte - State of artCollaboration with ETH Zurich

1. Silicon nitrade deposition

2. Photoresist by spin coating

3. Exposure & Development

4. Plasma etching of silicon nitride

5. Deposition of electrolyte (PLD)

6. KOH wet etching of Si

7. Plasma etching of silicon nitride