Diapositive 1

1
"Materials for Solid Oxide Fuel Cells" G.
Dezanneau Structures, Properties and
Modelisation of Solids LaB. Ecole Centrale Paris
2
Outline of the talk

• Team "Materials for hydrogen
  technologies"
• Research activities
• Materials for Solid Oxide Fuel Cells
• Objectives of research in Solid Oxide Fuel Cells
• New electrolyte materials
• Conclusion

3
SPMS Materials for hydrogen technologies
" Materials for hydrogen technologies "

• Materials for hydrogen technologies
• - Solid Oxide Fuel Cells
• ? anion / protonic conductors
• ? mixed (ion electron) conductors for
  electrodes
• ? defects chemistry experimental and
  theoretical approach
• ? from the elaboration till the test of button
  cells
• - Hydrogen storage
• - Hydrogen production High temperature
  electrolysis water Photolysis

4

• Team "Materials for hydrogen technologies"
• Research activities
• Materials for Solid Oxide Fuel Cells
• Objectives of research in Solid Oxide Fuel Cells
• New electrolyte materials
• Conclusion

5
What is a fuel cell ?

• Energy converter that transforms chemical energy
  from H2 (and O2) into electricity and heat
• Can be seen as a Continuous battery
• Runs as long as fuel and air (oxidant) are
  supplied

H2
H2 O2- ? H2O 2e-
H2O
Interconnexion materials
2e-
Anode
O2-
O2-
O2-
Cathode
2e-
1/2O2 2e- ? O2-
O2
Air
N2

• High efficiency (till 85 in a cogeneration
  mode)
• Environmental friendly
• Noise free and no site restriction

6
SOFCs challenge
H2
H2O
Interconnexion materials
H2 O2- ? H2O 2e-
2e-
Anode
O2-
O2-
O2-
Cathode
2e-
1/2O2 2e- ? O2-
O2
Air
N2

• Limitation high working temperature 900
  1000 ºC
• ? High Cost (ceramics interconnexion materials)
• ? Accelerated materials ageing

Research objective ? working temperature ( 600
800 ºC)
Find a configuration with the same transport
properties BUT at lower temperature
Minimise Internal ohmic losses (Rcell
Relectrolyte Relectrode)
?
7
SOFCs challenge
How to minimise internal losses ?
? Playing on geometry
Electrolyte-supported Fuel Cells
8
SOFCs challenge
How to minimise internal losses ?
? Playing on geometry thin electrolytes
? thin electrolyte deposition by screen-printing
(1)
Side view
Top view
Full Density (1350ºC) Crack free
(1) A. Tarancon, A. Morata, Ph.D. theses,
University of Barcelona
9
SOFCs challenge
How to minimise internal losses ?
? Playing on geometry thin electrolytes
? thin electrolyte deposition by screen-printing
(1)
? Playing on materials
(1) A. Tarancon, A. Morata, Ph.D. theses,
University of Barcelona
10
SOFCs challenge
How to minimise internal losses ?
? Playing on geometry thin electrolytes
? thin electrolyte deposition by screen-printing
(1)
? Playing on materials New electrolyte materials

• New anion conductors La9.33xSi6O263/2x
• Proton conductors La6-xMoO12-3/2x,
  BaSn1-xMxO3-d (2)

? Playing on materials New electrode materials
? GdBaCo2O5.5d cobaltite a new electrode
material (1, 3)
(1) A. Tarancon, A. Morata, PhD theses,
University of Barcelona
(2) PhD theses of Y. Wang and M.D. Braida, SPMS
Lab.
(3) PhD Thesis of Y. Hu, SPMS Lab.
11
SOFCs New electrode materials
Mixed ion-electron conducting material

• A very low value of R0.3 ?.cm2 already reached
  at 625C
• Current work on Co substitution by Fe or Ni to
  improve electrical
• and chemical properties

12
SOFCs challenge
How to minimise internal losses ?
? Playing on geometry thin electrolytes
? thin electrolyte deposition by screen-printing
(1)
? Playing on materials New electrolyte materials

• New anion conductors La9.33xSi6O263/2x
• Proton conductors La6-xMoO12-3/2x,
  BaSn1-xMxO3-d (2)

? Playing on materials New electrode materials
? GdBaCo2O5.5d cobaltite a new electrode
material (3)
(1) A. Tarancon, A. Morata, PhD theses,
University of Barcelona
(2) PhD theses of Y. Wang and M.D. Braida, SPMS
Lab.
(3) PhD Thesis of Y. Hu, SPMS Lab.
13
New compositions Apatite compounds
Lanthanum silicate apatite La9.33x(SiO4)6O23x/
2
T (C)
900
800
700
600
500
102
x - 0.04
La3
x 0.27
x 0.59
101
Zr0.90Y0.10O2.95
O2-
log s.T (S.cm-1.K)
100
(SiO4)4-
10-1
0.8
0.9
1.0
1.1
1.2
1.3
1.4
Yoshioka et al., J. Alloys Comp. (2006)
103/T (K-1)
? Potential candidate to replace
yttria-stabilised zirconia (YSZ) ? pour T lt
650C ? s (LSO) gt s (YSZ)
14
Apatites challenge

• Densification very difficult
• ? use as an electrolyte impossible

Objective ? Original and efficient synthesis
? Elaboration of dense ceramics ? Influence of
microstructure and composition on conductivity
(La9.33xSi6O263/2x x 0, 0.27, 0.47, 0.67)
15
Apatites nanopowders synthesis
Freeze-drying sublimation under vacuum of a
frozen solution homogeneous at a molecular scale
? preparation of a very divided precursor
La(CH3COO)3.1.5H2O TEOS CH3COOH
Cryocristallisation pulverisation in liquid N2
Solution cryo-cristallised
Freeze-drying
Calcination
Nanocrystalline powder La9.33xSi6O263x/2 (0 x
0.67)
Very divided Precursor
? Pure cristallised phase at Tcalcination gt
900C ? Porous resulting powder high specific
surface (gt 12 m2/g) ? good reactivity expected
during sintering
16
Apatites Sintering routes
Conventional sintering
Spark Plasma Sintering
Nanopowders
Nanopowders
P (50MPa)
pulses of current
Uniaxial pressing Green compacity ( 40)
Cold Isostatic Pressing (750 MPa / 10 min) Green
compacity ( 65)
P
Sintering 1200C - 1600C / 12h
sintering 1200C and 1500C several min.
The objective was to obtain dense ceramics (gt95)
at temperatures as low as possible
17
Apatites Conventional sintering
1 µm
La9.33Si6O26
1 µm
La9.6Si6O26.4
1 µm
La9.8Si6O26.7
1 µm
La10Si6O27
? Very good densification even at low temperature
? Strong influence of lanthanum content on
densification
18
Apatites SPS at 1200C vs 1500C
1200C
1500C
? Vitrous/transparent aspect of SPS-sintered
samples ? 1200C and 1500C ? very high
density 100 ? nanostructure at 1200C vs
microstructure at 1500C
19
Apatites Impedance spectroscopy

• La9.33Si6O26
• SPS 1200C
• La9.33Si6O26
• SPS 1500C

? At low T and high T, the contributions of Bulk
and Grain boundaries are difficult to
separate ? Only the total conductivity
will be considered
20
Apatites Electrical measurements
Conductivity at 700C
Conventional sintering
Spark Plasma Sintering

• ? Strong influence of porosity (conventional
  sintering)
• Small grain size leads to bad conductivity
• ? Blocking effect of grain boundary ( ? to
  current )

21
Conclusion
? Results on apatites ? Very reactive powders
obtained by freeze-drying ? Density higher than
98 obtained at 1500C
? Good control of grain size (from 100 nm till 10
mm) by SPS technology

• Better results are obtained by conventional
  sintering due to a greater
• grain size
• sapatite(700C) 1.3 10-2 S.cm-1 gt szircone
  (700C) 1 10-2 S.cm-1

? Future work building and test of a button cell
22
Many thanks to C. Bogicevic, F. Karolak (ECP,
Chatenay-Malabry) A. Chesnaud (ENSMP, Evry) C.
Estournès (CIRIMAT, Toulouse) A. Tarancon, A.
Morata, F. Peiro (Univ. Barcelona,
Spain) Thanks a lot for your attention
Contact guilhem.dezanneau_at_ecp.fr