Development of Nano-Structured Solid Oxide Fuel Cell ... · [48-124] La0.6 Sr0.4 Co0.8 Fe0.2 O3 /...
Transcript of Development of Nano-Structured Solid Oxide Fuel Cell ... · [48-124] La0.6 Sr0.4 Co0.8 Fe0.2 O3 /...
Development of Nano-Structured Solid Oxide Fuel Cell Electrodes
G. Schiller, S.A. Ansar, M. Müller
German Aerospace Center (DLR), Institute of Technical Thermodynamics, Pfaffenwaldring 38-48, D-70569 Stuttgart, Germany
17th Annual International Conference on Composites/Nano Engineering (ICCE-17),Honolulu, July 26-31, 2009
Outline
Introduction Principle of planar SOFCDLR spray concept for SOFC
Nanostructured Cathode by using Deposition from liquid precursors RF Plasma Technology (TPCVD) Phase purity
Structure
Nanostructured Anode by using Agglomerated nanoparticlesDC Plasma Technology Suspension plasma spraying (SPS)
Solution precursor plasma spraying(SPPS)
Conclusion
Design and Principle of a Planar SOFC
Air
ReactionProducts
Fuel Gas
CathodeElectrolyteAnode
Bipolar Plate
UnconvertedAir
O2
H O2H O2
O2O2
H2
Load
Anode
Cathode
SolidElectrolyte
O2-
O2O2
H O2
H2H2
O2-
O2- O2-
+
- A
E
M
SOFC Metal-Supported Cell
30 m
25 m
35 mBipolar plate
Bipolar plate
porous metallic substrateanodeelectrolyte
contact layercathode current collectorcathode active layer
protective coating
not used airoxygen/air
air channel
fuel channel
fuel brazing not used fuel + H O2
(not in scale)
Plasma Deposition Technology
Thin-Film Cells
Ferritic Substrates and Interconnects
Compact Design with Thin Metal Sheet Substrates
Brazing, Welding and Glass Seal as Joining and Sealing Technology
Plasma Spray Laboratory at DLR Stuttgart
Experimental Setup
~Tasks:
spray angle 10-20°homogeneous spray (narrow droplet size distribution)
Present solution:
“air assist atomizer”:disintegration of liquid stream in gas jet
Atomization
Problems:
small dimensionsextremely high temperature
precursorgas
atomizing gas
z-adjustableRF plasma torch
peristalticpump
liquidprecursor
injection probecentral gassheath gas
500 KHz generator
plasma
coating
x-y-movablesubstrate
vacuumpump
window
vacuumreactor
Applied Precursor Solutions and Desired Synthesis Products
Synthesis product Precursor Concentration
A La0.9Sr0.1MnO3 (LSM)La(NO3)3 • 6 H2OSr(NO3)2Mn(NO3)2 • 4 H2O
0,9 M0,1 M1,0 M
B La0.5Sr0.5MnO3 (LSM)La(NO3)3 • 6 H2OSr(NO3)2Mn(NO3)2 • 4 H2O
0,5 M0,5 M1,0 M
C La0.65Sr0.3MnO3 (ULSM)La(NO3)3 • 6 H2OSr(NO3)2Mn(NO3)2 • 4 H2O
0,65 M0,3 M1,0 M
D Pr0.65Sr0.3MnO3 (UPSM)Pr(NO3)3 • 5 H2OSr(NO3)2Mn(NO3)2 • 4 H2O
0,65 M0,3 M1,0 M
E La0.8Sr0.2FeO3 (LSF)La(NO3)3 • 6 H2OSr(NO3)2Fe(NO3)3 • 9 H2O
0,8 M0,2 M1,0 M
F La0.8Sr0.2(Co,Fe)O3 (LSCF)
La(NO3)3 • 6 H2OSr(NO3)2Co(NO3)2 • 6 H2OFe(NO3)3 • 9 H2O
0,8 M0,2 M0,5 M0,5 M
G La0.58Sr0.4Fe0.8Co0.2O3(LSFC)
La(NO3)3 • 6 H2OSr(NO3)2Fe(NO3)3 • 9 H2OCo(NO3)2 • 6 H2O
0,58 M0,4 M0,8 M0,2 M
H Pr0.58Sr0.4Fe0.8Co0.2O3(PSFC)
Pr(NO3)3 • 5 H2OSr(NO3)2Fe(NO3)3 • 9 H2OCo(NO3)2 • 6 H2O
0,58 M0,4 M0,8 M0,2 M
X-Ray Diffraction Patterns of La0.9Sr0.1MnO3
25 35 45 55 65 75 852 Theta
Inte
nsity
(arb
itrar
yun
its)
LaMnO3
La2O3
25 35 45 55 65 75 852 Theta
Inte
nsity
(arb
itrar
yun
its)
LaMnO3
La2O3
LaMn perovskiteKey parameter:
Mn loss depends onradial distance fromplasma jet axis
Top: TPCVD coatingfrom central part of plasma jet
Bottom: TPCVD coatingfrom cooler margin
stationary substrate
X-Ray Diffraction Patterns of Pr0.58Sr0.4Fe0.8Co0.2O3
Top: TPCVD coatingfrom central part of plasma jet
Bottom: TPCVD coatingfrom cooler margin
stationary substrate
Microstructure of TPCVD Perovskite Coatings
Functional Principle of DC Plasma
Powder Jet
Subs
trat
e
Plasma GunParticle Melting and Acceleration
Particle Impingement
Pla
sma
Gas
es
ArH2N2He
Splat Layering
Coating
Particle Injection
Vacuum Plasma Spraying of SOFC Cells
NiO+YSZ Powder
Co-precipitation and Spray-Drying
22 vol%NiO + YSZ
Agglomerated
Agglomerate size: -50+10 µm
Primary particle size: 20-80 nm
Feedstock Powder for DC Plasma Spraying
As-Sprayed Anode Structure and XRD
2 µm
20 40 60 802 theta (°)
Z N
FeDeposit
Powder
ZZ
Z
NN
NiO+YSZ Plasma Sprayed Deposit
Particle size in deposit was 60-220 nm compared to 20-80 nm for the feedstock powder
Ni(II)O and cubic-YSZ were the phases detected by XRD 34 38 42 462 theta (°)
Z
N
Z
PowderDeposit
N= Ni(II)O
Z= Cubic-zirconia
Permeability of Anode
0
1
2
3
4
5
AS Reduced AS Reduced
Conven. NiO+YSZ Nano NiO+YSZ
Per
mea
bilit
y C
oeff.
(10
-14 m
²)
0
100
200
300
400
500
600
0 100 200 300 400 500
Time (h)
σ (Ω
/cm
)
0100200300400500
0 15 30 45
Time (h)σ (Ω
/cm
) Conventional AnodeNano Anode
Con
d(1
/ohm
.cm
)
Con
d(1
/ohm
.cm
)
Conductivity of Nano-Anode
Conductivity of nano and conventional anode were comparable for first 30 to 40 hrs
Conductivity of nano anode increased for extended period of test time- possible cause could be Ni particles phase I sintering
Test Atmosphere
2 slm Ar+5 vol% H2
Electrochemical Testing
1.017 V
1.074 V
230
292 309
0.00
0.20
0.40
0.60
0.80
1.00
1.20
0 100 200 300 400 500 600 700 800 900Current density i [mA/cm²]
Cel
l vol
tage
U [V
]
0
200
400
600
800
Pow
er d
ensi
ty p
[mW
/cm
²]
Reference cell with conventional anode (); Cell with nanostructured anode after 100 h (Δ) and after 1500 h (◊) of operation 800°C - Cell area 12.6 cm² - Gases: 0.5 slm H2+0.5 slm N2/2.0 slm air).
• Cells containing a nano anode show 34% higher power density• Anodic polarization at OCV of nano anode was 0.42 Ωcm² instead of 0.72 Ωcm²
for conventional anode • 3.33%/kh degradation rate for cells with nano anode is comparable to cells having
conventional anodes – No evidence of additional degradation due to nanomaterials
Nano Anode Structure after SOFC Operation
2 µm
2 µm
After 100 h of operation After 1500 h of operation
Limited grain growth and sintering Particle size: 60 to 220 nm after 100 h and 95 to 390 nm after 1500 hExpected mechanisms are phase I or gas-phase sintering
Suspension and Solution Precursor Plasma Spraying
Suspension Plasma SprayingInjection of nano-particles in plasma by suspending them in a liquid.
Solution Precursor Plasma SprayingIn-flight nano-particles synthesis by chemical reaction of metal salt precursors in plasma.
Suspension Plasma Spraying
YSZ 40 nm particles and development of stable suspension using Zeta potential
Development of stable suspensions
05
1015202530
0 2 4 6 8 10 12Dispersant [wt.%]
zeta
-pot
entia
l [m
V]
Nanostructured porous YSZ depositPorosity 35%
Outlook:Additon of NiO for anode and LSM for cathode
Conclusion
Nanostructured cathodes and anodes for SOFC were prepared by applying plasma deposition processes (RF and DC plasma)Two approaches were applied:- Introduction of pre-synthesized nanoparticles as agglomerates or
suspensions into the plasma- In-situ synthesis of nanomaterials and deposits from solutions of
metal saltsTPCVD cathodes initially exhibited undesired secondary phases whichwas overcome by adjusting the chemical composition of the precursormaterial. The microstructure was columnar type with very high openporosityFor 1500 hours of operation only limited growth of nanosized particleswas observed in SOFC anodesFurther improvement of the microstructure of anodes is in progressusing DC plasma suspension and solution precursor plasma spraying
Synthesis from Liquid Precursors in an RF Plasma
Why liquid precursors?cost reduction
continuous feeding of material
homogeneous distribution in the plasma
synthesis of thermally instable materials
simple adjustment of stoichiometry
Why r.f. plasma?
large volume, low jet velocity, i.e. more complete synthesis
axial material injection
electrodeless, i.e. oxidizingconditions possible
central gassheath gas
induction coil
flange
exit nozzle
ceramic tube
quartz glas tube
gas distributor
polymer body
injection probe
precursors andatomization gas
X-Ray Diffraction Patterns of La0.58Sr0.4Fe0.8Co0.2O3
2Theta30.0 40.0 50.0 60.0 70.0 80.00.0
100.0
200.0
300.0
400.0
500.0
600.0
Abs
olut
e In
tens
ity
LSFC auf Cr5Fe, TPCVD, zentrum, HF0224[48-124] La0.6 Sr0.4 Co0.8 Fe0.2 O3 / Cobalt Strontium Iron Lanthanum O
[5-602] La2 O3 / Lanthanum Oxid
2Theta30.0 40.0 50.0 60.0 70.0 80.00
400
800
1200
1600
2000
Abso
lute
Inte
nsity
LSFC auf Cr5Fe, TPCVD, Rand, HF0224[48-124] La0.6 Sr0.4 Co0.8 Fe0.2 O3 / Cobalt Strontium Iron Lanthanum O
[34-396] Fe - Cr / Iron Chromium
Top: TPCVD coatingfrom central part of plasma jet
Bottom: TPCVD coatingfrom cooler margin
stationary substrate
IUR
cmS
AR
lel
ΔV
I = 10 mA
0
100
200
300
400
500
600
700
800
900
0 10 20 30 40 50 60Operation Time / h
Tem
pera
ture
/ °C Temperature
l
Atmosphere:Purge gas (Ar / 5vol% H2)
Electrical Conductivity Measurement
0.5 slpm H2 + 0.5 slpm N2
2,0 slpm Air
Gas volume flowanodecathode
12.57 cm2Effective area800°COperating temperature
Air
H2 + N2
1 SOFC2 Gold sealing3 Platinum net4 Glass sealing5 Housing6 Weight
Electrochemical Testing of Full Cells