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Enhancement of SOFC Cathode Electrochemical Performance Using
Multi-Phase Interfaces
Dane Morgan, Yueh-Lin LeeDepartment of Materials Science and Engineering
University of Wisconsin – Madison, WI USA
Stuart Adler, Timothy (TJ) McDonaldDepartment of Chemical Engineering
University of Washington, Seattle, WA USA
Yang Shao-Horn, Dongkyu (DK) Lee, Xiao (Renshaw) Wang Department of Mechanical Engineering
Massachusetts Institute of Technology, Boston, MA USA
16th Annual SECA WorkshopPittsburgh, PA
July 14 – 16, 2015 1
Acknowledgements
External Collaborators• Briggs White (NETL)• Michael D. Biegalski, H.M. Christen (Oak
Ridge National Laboratory)• Paul Fuoss, Edith Perret, Brian Ingram,
Mitch Hopper, Kee-Chul Chang (Argonne National Laboratory)
• Zhan Zhang, Christian M. Schlepuetz, Lynette Jirik (ID-33 of Advanced Photon Source)
• Paul Salvador (Carnegie Melon University)
MIT Skoltech Center For Electrochemical Energy Storage
King Abdullah University of Science andTechnology
Computing Support
National Energy Research Scientific Computing Center
Oak Ridge National Laboratory
NSF Supercomputing
DE-FE0009435, DESC0001284 2
Oak Ridge National Laboratory
Funding Support
Oxide Heterointerface for SOFC Cathodes
Interface of two oxides: Enhances ORR kinetics by ordersof magnitude compared to individual phases1-4
3
LSC-113: ABO3 Perovskite(AO-BO2 stacking)Cathode Material
LSC-214: K2NiF4 type AO-AO-BO2 stacking, coating
LSC-113LSC-214
Novel Heterostructure
Enhances ORR kinetics at 500-600°C
[1] E. J. Crumlin, et al., The Journal of Physical Chemistry Letters, 1, 3149-3155.[2] M. Sase, et al., Journal of The Electrochemical Society, 2008, 155, B793-B797.[3] M. Sase, et al., Solid State Ionics, 2008, 178, 1843-1852.[4] K. Yashiro, et al., Electrochem. Solid State Lett., 2009, 12, B135-B137.
Oxide Heterointerface for SOFC Cathodes
Interface of two oxides: Enhances ORR kinetics by ordersof magnitude compared to individual phases1-4
4
LSC-214: K2NiF4 type AO-AO-BO2 stacking, coating
[1] E. J. Crumlin, et al., The Journal of Physical Chemistry Letters, 1, 3149-3155.[2] M. Sase, et al., Journal of The Electrochemical Society, 2008, 155, B793-B797.[3] M. Sase, et al., Solid State Ionics, 2008, 178, 1843-1852.[4] K. Yashiro, et al., Electrochem. Solid State Lett., 2009, 12, B135-B137.
LSC-113: ABO3 Perovskite(AO-BO2 stacking)Cathode Material
Completed 33/36 months of project
1. How does this interfacialenhancement work in LSC113?
2. Can it be extended toXYZ214/LSCF113 interfaces?
3. Can we make more active, morestable porous electrodes withthese interfaces?
5
Conclusions1. How does this interfacial enhancement work in
LSC113?
Stabilization of Sr-rich LSC113 surface andsuppression of Sr-rich precipitation
2. Can it be extended to XYZ214/LSCF113 interfaces?
Yes! LSC214/LSC113/LSCF113 enhances LSCF113 10x!
3. Can we make more active, more stable porouscathodes with these interfaces?
Promising initial results but needs more workwith NETL, industry teams, future proposals …
Yang Shao-Horn (MIT)
Dane Morgan (U Wisc.) Stuart Adler (U Wash.)
LSC-214/LSCF-113 Films LSCF-113LSC-214
NLEIS + Rate modeling, LSC-214/LSCF-113 porous electrodes
Ab initio EnergeticsThermokinetic Modeling
Project Overview
6
Major Activities• PLD synthesis and physical (SEM, xray, Auger,
COBRA) electrochemical (EIS) characterization of LSC113, LSCF113, LSC214, LSN214, LSC214/LSC113 , LSC214/LSCF113, LSN214/LSC113, LSC113-LSC214/LSCF113.
• NLEIS, kinetic modeling, degradation testing of oxygen reduction for film/porous electrode LSC113and LSCF113.
• Ab initio calculations of defects and Srsegregation in LaSrMO4 (214), LSC113, LSCF113, LSC214/LSC113, LSC214/LSCF113.
7
Major Conclusions• LSC113: Sr segregates strongly to surfaces of LSC113 but is unstable at
these surfaces leading to precipitation and lost performance.
• LSC214/LSC113: Has enhanced performance because Sr is gettered by LSC214, which effectively stabilizes Sr-rich LSC113 surface and suppresses precipitation.
• LSCF113: Sr segregates very strongly to surfaces of LSCF113 and is relatively stable at these surfaces vs. LSC113.
• LSC214/LSCF113: Has little enhanced performance because Sr-rich LSCF214 is already fairly stable.
• LSC214/LSC113/LSCF113: Has enhanced performance due to enhanced activity of LSC214/LSC113 on the LSCF.
8
Major Conclusions• LSC113: Sr segregates strongly to surfaces of LSC113 but is unstable at
these surfaces leading to precipitation and lost performance.
• LSC214/LSC113: Has enhanced performance because Sr is gettered by LSC214, which effectively stabilizes Sr-rich LSC113 surface and suppresses precipitation.
• LSCF113: Sr segregates very strongly to surfaces of LSCF113 and is relatively stable at these surfaces vs. LSC113.
• LSC214/LSCF113: Has little enhanced performance because Sr-rich LSCF214 is already fairly stable.
• LSC214/LSC113/LSCF113: Has enhanced performance due to enhanced activity of LSC214/LSC113 on the LSCF.
9
Sr Segregation and Precipitation
Bulk Sr
La Co OSurface segregated Sr
SrOxPrecipitated Sr
10
CoO2
(La,Sr)OCoO2
(La,Sr)O
Surface Terminations of (001) (La,Sr)CoO3
11
What Termination/Segregation is Stable?
12
AO surface is stable over CoO2, and Sr-rich is stable over La-rich. Consistent with data from Auger spectroscopy, LEIS, COBRA, etc.
(001) (La0.75Sr0.25)CoO3, 550°C, 1atm
D Lee, J Mater Chem A 2015
What Precipitation is Stable (SEM)?
13
Surface is unstable with respect to Sr-rich precipitates
(001) (La0.80Sr0.20)CoO3 550°C D Lee, J Mater Chem A 2015
Pristine 70h Anneal
What Precipitation is Stable (COBRA)?
14
Surface is unstable with respect to Sr enriched precipitates
(001) (La0.80Sr0.20)CoO3
Coherent Brag Rod Analysis (COBRA)
Feng et al., Energy Environ. Sci. 2014; Feng et al., J Phys. Chem. Lett. 2014
What Precipitation is Stable (DFT)?
15
Surface is unstable with respect to Sr enriched precipitates
Further Evidence for Segregation/Precipitation Effects
(NLEIS)
16
Non-Linear Electrochemical Impedance Spectroscopy (NLEIS)
C. Kreller et al., JES ‘13
• Excellent agreement with NLEIS data.
• Implies both Sr segregation and lateral Sr inhomogeneity.
• xs(2) ~0.4 for LSC-82, xs
(1) ~ 0.45.
-10.0
-8.0
-6.0
-4.0
-2.0
-5 -4 -3 -2 -1 0
What Surfaces are Active?
17
CoO2 surface best, SrO next best, LaO surface inactiveLog10[PO2 (atm)]
Log
10[k
tr(m
/s)]
van der Haar et al., JES ’02Egger et al. SSI ‘12
M. Gadre et al, Submitted ‘15
LaO Termination
(001) (La0.5Sr0.5)CoO3 650°C
-2
-4
-6
-20
Summary of Stability and Activity
18
(001) (La0.5Sr0.5)CoO3 650°C
CoO2 Termination
Log
10[k
tr(m
/s)]
LaO Termination
SrO Termination
SrO Termination +Sr-rich Precipitates
Increasing stability
Major Conclusions• LSC113: Sr segregates strongly to surfaces of LSC113 but is unstable at
these surfaces leading to precipitation and lost performance.
• LSC214/LSC113: Has enhanced performance because Sr is gettered by LSC214, which effectively stabilizes Sr-rich LSC113 surface and suppresses precipitation.
• LSCF113: Sr segregates very strongly to surfaces of LSCF113 and is relatively stable at these surfaces vs. LSC113.
• LSC214/LSCF113: Has little enhanced performance because Sr-rich LSCF214 is already fairly stable.
• LSC214/LSC113/LSCF113: Has enhanced performance due to enhanced activity of LSC214/LSC113 on the LSCF.
19
Major Conclusions• LSC113: Sr segregates strongly to surfaces of LSC113 but is unstable at
these surfaces leading to precipitation and lost performance.
• LSC214/LSC113: Has enhanced performance because Sr is gettered by LSC214, which effectively stabilizes Sr-rich LSC113 surface and suppresses precipitation.
• LSCF113: Sr segregates very strongly to surfaces of LSCF113 and is relatively stable at these surfaces vs. LSC113.
• LSC214/LSCF113: Has little enhanced performance because Sr-rich LSCF214 is already fairly stable.
• LSC214/LSC113/LSCF113: Has enhanced performance due to enhanced activity of LSC214/LSC113 on the LSCF.
20
Sr Gettered by LSC214 and Stabilized at LSC214/LSC113Interface
21Sr in interface and LSC214 film and depleted from LSC113
Z. Feng, et al., JPCL ‘14
LSC214 Decoration Suppresses Sr-Rich Phase Precipitation
22
(LaSr)CoO4(La0.80Sr0.20)CoO3 550°C
LSC113
LSC214/LSC113
Pristine 70h AnnealD. Lee, J Mater Chem A 2015
LSC214 Decoration Enhances LSC113Activity and Stability
23
D Lee, J Mater Chem A 2015
(LaSr)CoO4, (La0.80Sr0.20)CoO3 550°C
Major Conclusions• LSC113: Sr segregates strongly to surfaces of LSC113 but is unstable at
these surfaces leading to precipitation and lost performance.
• LSC214/LSC113: Has enhanced performance because Sr is gettered by LSC214, which effectively stabilizes Sr-rich LSC113 surface and suppresses precipitation.
• LSCF113: Sr segregates very strongly to surfaces of LSCF113 and is relatively stable at these surfaces vs. LSC113.
• LSC214/LSCF113: Has little enhanced performance because Sr-rich LSCF214 is already fairly stable.
• LSC214/LSC113/LSCF113: Has enhanced performance due to enhanced activity of LSC214/LSC113 on the LSCF.
24
Major Conclusions• LSC113: Sr segregates strongly to surfaces of LSC113 but is unstable at
these surfaces leading to precipitation and lost performance.
• LSC214/LSC113: Has enhanced performance because Sr is gettered by LSC214, which effectively stabilizes Sr-rich LSC113 surface and suppresses precipitation.
• LSCF113: Sr segregates very strongly to surfaces of LSCF113 and is relatively stable at these surfaces vs. LSC113.
• LSC214/LSCF113: Has little enhanced performance because Sr-rich LSCF214 is already fairly stable.
• LSC214/LSC113/LSCF113: Has enhanced performance due to enhanced activity of LSC214/LSC113 on the LSCF.
25
What Termination/Segregation is Stable?
26
AO surface is stable over CoO2, and 100% Sr is stable for LSCF, vs. ~75% for LSC. Stronger surface segregation of Sr for LSCF!
(001) (La0.75Sr0.25)CoO3, (La0.625Sr0.375)(Co0.2Fe0.8)O3, 550°C, 1atm
D Lee, J Mater Chem A 2015
Sr = 1.0
Sr= 0.75
Sr=0.5
Sr=0.25
Sr=0.0
LSC113 LSCF113
D. Lee, J Mater Chem A 2015
Is Sr Stable in LSCF Surface (DFT)?
27
Sr is more stable in Sr-rich LSCF surface than Sr-rich LSC surface
LSCF113 Sr-Rich Surface More Stable than LSC113
28
(La0.80Sr0.20)CoO3(La0.6Sr0.4)(Co0.2Fe0.8)O3 550°C
LSC113
LSCF113
Pristine 70h AnnealD. Lee, J Mater Chem A 2015
Evidence for Segregation/Precipitation Effects in LSCF (NLEIS)
• Inhomogeneous thermodynamics needed to fit data
• ~3 nm of Sr-rich phase at surface• Surface thermodynamics similar to
Sr-rich phase• Total [SrLa
’] < 0.4 (i.e. possible Srprecipitation) 29
Bulk Strontium DistributionPhase 1: [SrLa
’] = 0.15, 87% vol.Phase 2: [SrLa
’] = 0.85, 13% vol.
Surface KineticsRO2
0 ∝ pO2 xv2(1-xh)2
[SrLa’] = 0.9
(La0.6Sr0.4)(Co0.2Fe0.8)O3 Film, 600°C
Major Conclusions• LSC113: Sr segregates strongly to surfaces of LSC113 but is unstable at
these surfaces leading to precipitation and lost performance.
• LSC214/LSC113: Has enhanced performance because Sr is gettered by LSC214, which effectively stabilizes Sr-rich LSC113 surface and suppresses precipitation.
• LSCF113: Sr segregates very strongly to surfaces of LSCF113 and is relatively stable at these surfaces vs. LSC113.
• LSC214/LSCF113: Has little enhanced performance because Sr-rich LSCF214 is already fairly stable.
• LSC214/LSC113/LSCF113: Has enhanced performance due to enhanced activity of LSC214/LSC113 on the LSCF.
30
Major Conclusions• LSC113: Sr segregates strongly to surfaces of LSC113 but is unstable at
these surfaces leading to precipitation and lost performance.
• LSC214/LSC113: Has enhanced performance because Sr is gettered by LSC214, which effectively stabilizes Sr-rich LSC113 surface and suppresses precipitation.
• LSCF113: Sr segregates very strongly to surfaces of LSCF113 and is relatively stable at these surfaces vs. LSC113.
• LSC214/LSCF113: Has little enhanced performance because Sr-rich LSCF214 is already fairly stable.
• LSC214/LSC113/LSCF113: Has enhanced performance due to enhanced activity of LSC214/LSC113 on the LSCF.
31
Sr More Weakly Attracted by LSC214 form LSCF113 ThanLSC113 (DFT)
32
D. Lee, J Mater Chem A 2015
LSC214 Decoration Has Little Effect on Sr-Rich Phase Precipitation in LSCF
33
(LaSr)CoO4(La0.80Sr0.20)CoO3(La0.6Sr0.4)(Co0.2Fe0.8)O3550°C
LSCF113
LSC214/LSCF113
Pristine 70h AnnealD. Lee, J Mater Chem A 2015
LSC214 Decoration Has Little Impact on LSCF113 Activity
34D Lee, J Mater Chem A 2015
LSC214/LSC113 LSC214/LSCF113
LSC214 Decoration Has Little Impact on LSCF113 Activity and Stability
35
D Lee, J Mater Chem A 2015
(LaSr)CoO4, (La0.80Sr0.20)CoO3, (La0.6Sr0.4)(Co0.2Fe0.8)O3 550°C
LSC214/LSC113 LSC214/LSCF113
10~100X ~2X
Major Conclusions• LSC113: Sr segregates strongly to surfaces of LSC113 but is unstable at
these surfaces leading to precipitation and lost performance.
• LSC214/LSC113: Has enhanced performance because Sr is gettered by LSC214, which effectively stabilizes Sr-rich LSC113 surface and suppresses precipitation.
• LSCF113: Sr segregates very strongly to surfaces of LSCF113 and is relatively stable at these surfaces vs. LSC113.
• LSC214/LSCF113: Has little enhanced performance because Sr-rich LSCF214 is already fairly stable.
• LSC214/LSC113/LSCF113: Has enhanced performance due to enhanced activity of LSC214/LSC113 on the LSCF.
36
Major Conclusions• LSC113: Sr segregates strongly to surfaces of LSC113 but is unstable at
these surfaces leading to precipitation and lost performance.
• LSC214/LSC113: Has enhanced performance because Sr is gettered by LSC214, which effectively stabilizes Sr-rich LSC113 surface and suppresses precipitation.
• LSCF113: Sr segregates very strongly to surfaces of LSCF113 and is relatively stable at these surfaces vs. LSC113.
• LSC214/LSCF113: Has little enhanced performance because Sr-rich LSCF214 is already fairly stable.
• LSC214/LSC113/LSCF113: Has enhanced performance due to enhanced activity of LSC214/LSC113 on the LSCF.
37
Enhancement from Mixed Single Layer [LSC214+LSC113]/LSCF113
550 °C
38
• ~10x enhancement in surface exchange of LSCF113!• From catalytic ability of LSC214+LSC113?
Enhancement from Double Layer StackedLSC214/LSC113/LSCF113
550 °C
39
• ~10x enhancement in surface exchange of LSCF113!• From catalytic ability of LSC214/LSC113?• Strong Sr dependence (qualitatively consistent with previous
observations of Sr being critical) and best for largest Sr content
40
Conclusions1. How does this interfacial enhancement work in
LSC113?
Stabilization of Sr-rich LSC113 surface andsuppression of Sr-rich precipitation
2. Can it be extended to XYZ214/LSCF113 interfaces?
Yes! LSC214/LSC113/LSCF113 enhances LSCF113 10x!
3. Can we make more active, more stable porouscathodes with these interfaces?
Promising initial results but needs more workwith NETL, industry teams, future proposals …
END
Thank you for your attention
41