Improving the electrolyte/ cathode assembly for advanced Solid Oxide Fuel Cells

1
Improving the electrolyte/ cathode assembly for
advanced Solid Oxide Fuel Cells

• N. Hildenbrand, B.A. Boukamp, D.H.A. Blank (a)
• P. Nammensma, G. Rietveld (b)
• (a) MESA Institute for Nanotechnology
• (b) Energy research Centre Netherlands

2
SOFC, a challenge
3
SOFC, a challenge

• Power density delivered by SOFC in W/cm2
• P Emf x i ASR x i2
• where
• - Emf is electromotive force, ca. 1V
• - i is current density, A/cm2
• - ASR is Area Specific Resistance O.cm2

4
SOFC, a challenge

• ASR economic obstacle
• - Electrolyte and electrode reaction
  resistances
• - Gas diffusion limitations
• - Change of gas compositions
• - Contact resistance in all interfaces

Søren Linderoth, 2007

• Target ASR value 0.1 O.cm2 at the lowest
  temperature possible.

5
What brings nanotechnology?

• Improve electrolyte / cathode interface.

Porous LSCF, 53 µm
Electrolyte 3YSZ, 92 µm
Interlayer YDC, 1-4 µm
LSCF La0.6SrO.4Co0.2Fe0.8O3-d YSZ Yttira
Stabilized Zirconia YDC Yttria Doped Ceria
6
What brings nanotechnology?

• Combination of dense and porous electrode

Porous LSCF, 53 µm
Electrolyte 3YSZ, 92 µm
Dense LSCF 200 nm
Interlayer YDC, 1-4 µm
LSCF La0.6SrO.4Co0.2Fe0.8O3-d YSZ Yttira
Stabilized Zirconia YDC Yttria Doped Ceria
7
Microstructure

• 2 types of microstructure

8
Microstructure with LSCF as cathode

• Sample type P

9
Microstructure with LSCF as cathode

• Sample type DP

ZOOM
10
Microstructure with LSCF as cathode

• Sample type DP

Porous LSCF  Dense  LSCF YDC YSZ
N.Hildenbrand, B.A.Boukamp, N.Nammensma,
D.H.A.Blank, doi10.1016/j.ssi.2010.01.028.
11
Area Specific Resistance
ASR
ASR
ASR improved by factor 3
Why do we observe such an improvement ???
12
Analysis

• The ALS model 1-2 leads to a Gerischer
  response.
• Competition between surface
  transport and bulk transport.
• v surface / bulk
  transport
• Limitation by surface
  exchange and bulk
  diffusion.
• Qualitatively
• Ds gtgt Ka Dv

e-
O2
e-
O2
O2-
O2-
O2-
1 S.B. Adler, J.A. Lane, B.C.H. Steele,
J.Electrochem.Soc. 143 (1996) 3554-64 2 Y. Lu,
C. Kreller, S.B. Adler, J.Electrochem.Soc. 156
(2009) B513
13
Impedance characteristics of both cells at 600ºC
in air
ASR
ASR
14
Model equivalent circuit
N.Hildenbrand, B.A.Boukamp, N.Nammensma,
D.H.A.Blank, Solid State Ionics, to be submitted.
15
pO2 dep. op Gerischer parameters at 600C

• Variation as P(O2) to the power m
• mP (Ka) 0.62 (ALS 0.64)
• mP (Z0) 0.17 (ALS 0.30)

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pO2 dep. op Gerischer parameters at 600C

• Variation as P(O2) to the power m
• mP (Ka) 0.62 (ALS 0.64)
• mP (Z0) 0.17 (ALS 0.30)

• Variation as P(O2) to the power m
• mDP (Ka) 0.25 (ALS 0.64)
• mDP (Z0) 0.76 (ALS 0.30)

The mechanism of oxygen reduction is changed!
17
Analysis - Concept
Dv
18
Analysis - Concept

• Ds gtgt Dv Ds gtgt Ka 1-2
• Accumulation of Oad on the surface of the MIEC at
  the base of each rod.

1 S.B. Adler, J.A. Lane, B.C.H. Steele,
J.Electrochem.Soc. 143 (1996) 3554-64 2 Y. Lu,
C. Kreller, S.B. Adler, J.Electrochem.Soc. 156
(2009) B513
Dv
19
Analysis - Concept

• Ds gtgt Dv Ds gtgt Ka 1-2
• Accumulation of Oad on the surface of the MIEC at
  the base of each rod.

1 S.B. Adler, J.A. Lane, B.C.H. Steele,
J.Electrochem.Soc. 143 (1996) 3554-64 2 Y. Lu,
C. Kreller, S.B. Adler, J.Electrochem.Soc. 156
(2009) B513
Dv
20
Analysis - Concept

• More active sites at the base of each rod for
  surface exchange.

Dv
21
Analysis - Concept

• More active sites at the base of each rod for
  surface exchange.

Dv
22
Conclusion

• Improvement of the Area Specific Resistance by a
  factor 3 for LSCF.
• Decrease working temperature of 75ºC for LSCF.
• It works for other materials.
  http//doc.utwente.nl/78272/
• The oxygen reduction mechanism is changed
• Concept to explain this phenomenon.

23
Outlook

• Advanced Dutch Energy Materials Innovation Lab
  ADEM projects
• Funding by Ministerie van Economische Zaken (EZ).
• Collaboration between the 3 TU.
• 2 PhD projects within IMS
• - Advanced materials for SOFC anode.
• - Development of thin films deposition
  techniques for SOFC electrolytes.

24
Acknowledgements

• Project funded by SenterNovem, agency of the
  Dutch Ministry of the Economic Affairs, promoting
  sustainable development and innovation, both
  within the Netherlands and abroad.
• IMS group of University of Twente.