cathode contact material development library/events/2010/seca...cathode contact material development...
TRANSCRIPT
Cathode Contact Material Development
Michael C. Tucker*, Lei Cheng, Lutgard C. DeJonghe
Materials Sciences DivisionLawrence Berkeley National Laboratory
Berkeley, CA 94720
Pittsburgh, PAJuly 2010
Problem Statement
Bonding at 1000°C or less to avoid oxidation of steel
This is a low sintering/bonding temperature!!- poor bonding - incomplete sintering = reduced conductivity
- Loose powder CCM is acceptable if stack experiences uniform compression
BUT: cross-cell thermal gradients, warping of components, etc causes local variation - delamination and loss of electrical contact
Well-bonded CCM is desirable, but challenging
- Can we find a material that is reactive enough to bond at <1000°Cbut stable at 800°C operation?
Ni-YSZ anode
YSZ electrolyteLSCF cathode
441 stainless steel
(MnCo)3O4 coating
Contact material (CCM)
Contact between Crofer22APu and LSFPNNL Yang et al., Journal of Power Sources 155 (2006) 246–252
LSCM
Contact between Crofer22APU and LSFIkerlan, Juelich Montero et al., Journal of Power Sources 188 (2009) 148–155
LSF
Crofer22APU/MCF/CCM/LSF
Crofer22APU/CCM/LSF
Enhancement of LSM SinteringMcCarthy et al., Journal of Power Sources 180 (2008) 294–300
Electrical resistivity of spinel-coated Crofer 22 APU/LSM-10 contact paste/spinel-coated Crofer 22 APU sandwich specimen versus time, measured in air at 800 ◦C.
Sinter at 900°C, switch between air and nitrogenenhance sintering by creation of transient defects
Observations from Literature
- 200h is enough to capture initial transient
- No standard test geometry
- No standard CCM paste application method
- Compressive load applied (bonding not typically tested)
- No consensus on “best” CCM
Candidate MaterialsLa0.6Sr0.4Co0.8Fe0.2 LSCFLa0.8Sr0.2Cu0.9Fe0.1O2.5 LSCuFLa0.7Sr0.3CoO3 LSCSm0.5Sr0.5CoO3 SSCSmBa0.5Sr0.5Co2O5 SBSCGdSrCo2O5 GSCLa0.65Sr0.30MnO3 LSMLaBaCo2O5 LBCYBaCo2O5 YBCNd1.8Ce0.2CuO4 NCCLa0.8Sr0.2Co0.3Mn0.1Fe0.6O3 LSCMFLa0.98Ni0.6Fe0.4O3 LNFLa1.2Sr0.8NiO4 LSNLa0.7Sr0.3FeO3 LSFLa2Ni0.6Cu0.4O4 LNC
LSM, LNF, SSC, LSCF purchased from Praxair
All others synthesized by GNP
CCM requirements:- good bonding- high electronic conductivity - good CTE match - chemical compatibility with LSCF
and (MnCo)3O4
Approach:Select candidates from cathode literature - high conductivity- low sintering temperature
GNP Synthesis, Coarsening, XRD Phase Confirmation
10 20 30 40 50 60 70 80
In
tens
ity (a
.u.)
2θ (degrees)
LSC
SBSC
NCC
LSCMF
LSF
800°C calcination
10 20 30 40 50 60
LBC 800°C
LBC 1100°C
LBC 1000°C
LBC 900°C
Inte
nsity
(a.u
.)2θ (Degrees)
800°C: LSC, SBSC, NCC, LSCMF, LSF900°C: GSC, LSN, LSCuF1100°C: LBC, YBC
CTE
Note CTE for interconnect and cell <14ppm/K
- Matched CTE is desirable
- High CTE does not disqualify candidate material
- Thin, porous layer
600 700 800 90012
14
16
18
20
22
24
26
LNCu
441
MnCo
CTE
(ppm
/K)
Temperature (°C)
LSCF
GSC
LSN
LSMLSF
NCC
LSCMF
LSCuF
YBC
LBC
SBSC
LNF
SSC
LSC
Conductivity of Porous CCM
650 700 750 800 850 900100
150
200
250
300
350
400
LSM sintered 1300°C
LSM sintered 1000°C
Con
duct
ivity
(S/c
m)
Temperature (°C)
(70% dense)
Conductivity less than predicted by density- minimal sintering/particle necking or GB issue
iV
~1cm
Pt wires/paste
Pt mesh/paste
Sintered bar of oxide
Conductivity of Dense CCM
600 650 700 750 800 850 900 950
100
1000
LSM
LSF
NCCLSCMF
LSCuFYBCLBC
LSNLSCFGSC
SBSC
LNF
SSC
Con
duct
ivity
(S/c
m)
Temperature (°C)
LSC
- Measured for dense bars
- Conductivity of porous CCM after bonding at 900-1000°C will be lower
600 700 800 900 1000 1100 1200 1300
-20
-15
-10
-5
0
LNCu
Per
cent
Lin
ear C
hang
e (%
)
Temperature (°C)
LSCF
GSC
LSN
LSM
LSF
NCCLSCMF
LSCuF
YBC
LBCSBSCLNF
SSCLSC
Sintering Behavior
- Only a few candidates display significant sintering in the 900-1000°C range
700 800 900 1000-10
-5
0
LNCu
Per
cent
Lin
ear C
hang
e (%
)
Temperature (°C)
LSCF
GSC
LSN
LSM
LSF
NCC
LSCMF
LSCuF
YBC
LBC
SBSC
LNF
SSCLSC
- Extent-of-sintering related to strength in the CCM layer
(not necessarily related to bonding at the interface with neighbor layers)
Reactivity with Neighbor Materials
20 30 400.0
0.5
1.0
LSCF + MCO1000°C 10h
LSCF
Inte
nsity
(a.u
.)
2θ (Degrees)
MCO
20 30 400.0
0.5
1.0
NCC + MCO1000°C 10h
NCC
Inte
nsity
(a.u
.)
2θ (Degrees)
MCO
Pellets of mixed MCO/CCM and LSCF/CCM Reacted in air at: Operating conditions (800°C 120h) and Sintering conditions (1000°C 10h)
Example: No Reaction Example: Significant Reaction
Most candidates were non-reactive with MCO, but reacted with LSCF
Reaction/Diffusion Distance
-10 0 10 20 30 40 50 60 70
0
50
100
150
200
250
300
Sig
nal I
nten
sity
(a.u
.)
Distance (μm)
Nd
Sr
La
Co
Fe
Ce
Cu
LSCF NCC
LSCF
NCC
In all cases, reaction zone restricted to <40μmreaction may be acceptable for
- thick LSCF layer- electrically conductive reaction products
EDAX
Screening Summary
Incipient Sintering Point (°C)
Shrinkage at 900°C
Shrinkage at 1000°C
CTE at
800°C800°C 150h
1000°C 10h
800°C 150h
1000°C 10h
Conductivity of bulk
dense pellet 800°C (S/cm)
LSCF 637 2.7 7.6 17.3 NO NO N/A N/A 426LSCuF 820 1.1 10.1 15.5 NO NO NO NO 201LSC 677 1.1 3.3 18.7 NO NO Minor Minor 1702SSC 740 0.5 2.3 22 NO Trace NO NO 1338SBSC 708 1.6 3.4 22 NO Trace YES YES 458GSC 760 1.3 3.2 19.5 NO Trace YES YES 350LSM 784 0.7 3.3 12.8 NO NO YES YES 272LBC 770 0.7 2.3 25 NO NO Minor Minor 314YBC 689 1.7 3.8 16.8 NO YES YES YES 260NCC 657 1.5 5.5 14.5 YES YES YES YES 107LSCMF 786 0.4 2.1 17.6 NO NO N/A N/A 110LNF 932 0 1.1 13.8 NO NO YES YES 589LSN 975 0 0.1 13.5 Minor YES NO NO 352LSF 690 0.3 0.9 13.3 NO NO NO NO 133LNC 782 0.4 2.4 14.6 NO NO NO NO 11
The most promising candidates are:- LSCF: good sintering and moderate conductivity- LSCuF: very good sintering at 1000°C- LSC and SSC: extremely high conductivity, moderate sintering
Reacts with MCO?
Reacts with LSCF?
ASR Measurement
NCC, LSC, LSCF and LSCuF show low and stable ASR
LSCF cathode(MnCo)3O4 coatingPrepared at PNNL
441 stainless steel
Contact material (CCM)
441 stainless steel
screen printed CCM and LSCF(PNNL ink recipe)
No compressive load
0 50 100 150 2000.0000
0.0025
0.0050
0.0075
0.0100
0.0125
0.0150
LSCuF
LSCFPt
App
aren
t AS
R(O
hm-c
m2)
Time (h)
LSC
SSC
NCC
800°C
Thermal Cycling
1 2 3 4 50.0000.0010.0020.0030.0040.0050.0060.0070.0080.0090.0100.0110.0120.0130.0140.015
SSC
LSC
LSCuF
AS
R (O
hm-c
m2 )
Thermal Cycle
NCC
21-800°C 10°C/min
No obvious delamination despite wide range of CTE
LSC Post-Mortem
25μm
LSC CCM
Porous LSCF
MCO
441 Steel
Sr
La
LaLa
La Fe
Co
-10 0 10 20 300.00
0.25
0.50
0.75
1.00
1.25
1.50
1.75
Fe/C
o S
igna
l int
ensi
ty (a
.u.)
Distance from Interface (μm)
Minor diffusion of Fe into LSC
Good bonding at LSC/LSCF interface
SSC Post-Mortem
441MCO
LSCF
SSC
441
MCODelamination at SSC/MCO interface (during sample prep?)
Good bonding at SSC/LSCF interface
SSC Post-Mortem
441
MCO
LSCF
SSC
SrSm Co
Co
SmSm
Sr La
LaLa
Fe
Co
Mn
Mn
Co
Co
No interdiffusion detected in bulk layers
CCM Layer Uniformity
- Wet-print on both substrates and assemble- Voids created during solvent burnout?
Develop alternative processing to ensure uniform contact - Print / dry / assemble- Print / dry print / assemble
441
CCM
LSCF
441
Voids
0 500 1000 15000.0
0.2
0.4
0.6
0.8
1.0
Current Density (mA/cm2)
Cel
l Pot
entia
l (V) 800°C
750°C
850°C
0
100
200
300
400
500
600
700
Pow
er Density (m
W/cm
2)
Commercial Cell Selection
0 500 10000.0
0.2
0.4
0.6
0.8
1.0
Current Density (mA/cm2)
Cel
l Pot
entia
l (V)
800°C
0
100
200
300
400
500
600
Power D
ensity (mW
/cm2)
0 50 1000.0
0.4
0.8
800°C
Cel
l Pot
entia
l (V
)
Time (h)
350mA/cm2air/H2-H2O
- $24 each for 25 cell batch- 350-425mW/cm2 at 0.7V- 25-38%/1000h degradation
Tape-cast cells from NIMTEwww.sofc.com.cn
0.0 0.5 1.0 1.5 2.00.0
-0.1-0.2-0.3-0.4-0.5
Z" (o
hm c
m2 )
Z' (ohm cm2)
800°C 750°C850°C
0.0 0.5 1.0 1.50.0
-0.5
Z" (o
hm c
m2 )
Z' (ohm cm2)
800°C
Future Directions
- Mix LSC (high conductivity) with LSCuF (good sintering)
- Sintering aids to improve bonding and mechanical properties after firing at 1000°C
- Identify new candidates from outside the SOFC world
- Reactive sintering
- Improve uniformity of CCM printing procedure
- In-depth post-mortem analysis
Thanks to Joe Stoffa and Briggs White
This work was supported by the US DOE through project MSD-NETL-01
Contact InfoMike Tucker [email protected]
Lut DeJonghe [email protected]