Core Research on Solid Oxide Fuel Cells, plus flexible
funding project “Application of 3D imaging and analysis to
the design of improved current collectors for SOFCs.”
Professor Nigel Brandon OBE FREng
BG Chair in Sustainable Gas
Imperial College London
Director: Hydrogen and Fuel Cell SUPERGEN Hub (H2FC SUPERGEN)
www.h2fcsupergen.com
www.imperial.ac.uk/energyfutureslab
Content
• Core - 3D Imaging and Analysis of Solid Oxide Fuel Cell
Electrodes.
• Flexible - Application of 3D imaging and analysis to the design
of improved current collectors for SOFCs
• Core - New approaches to SOFC electrode fabrication.
• Summary.
Ambition – to move to a move towards a design led approach to
optimum SOFC electrodes
Typical planar SOFC geometries
Brett DJL, Atkinson A, Brandon NP, Skinner SJ, Intermediate temperature solid oxide fuel cells, CHEM SOC REV, 2008, Vol:37,
Pages:1568-1578
SOFC Electrode Design
Illustration of the effect of extending the TPB using a MIEC electrolyte. (a)
Electrolyte / cermet anode with active TPB circled; (b) mechanism of
reaction at the TPB; (c) mechanism of reaction at the extended TPB.
Electrode Microstructure in three dimensions
TPB 2
TPB 1
TPB 3
X-ray
Microtomogaphy
100µm3
CT/Synchrotron
Mechanical
Sectioning
1µm3
Dual Beam
FIB Tomo
X-ray NCT
Electron
Tomo
10 nm3
Volume Size Analysis
10mm3
>1m3
Tomography techniques to resolve 3D microstructure
3D Atom
Probe
0.1 nm
10 nm
1µm
100µm
Combine multiple
tomographic techniques
 Functional Materials
Multi-scale Tomography
 FOV/Resolution
We can apply this to
SOFC/LIB electrodes
And other materials
………
1mm
1mm
1cm
>1m
Farid Tariq et al, Acta Materialia 59(5),2011
Page 6
Voxel Length Scale
Diagram After Uchic and Holzer, MRS Bulletin, 2007
Tomography of Ni-ScSZ electrodes
Ni
30 Vol.%
A
Ni
40 Vol.%
Ni
B
Ni
50 Vol.%
Ni
C
ScSZ
ScSZ
Pores
Pores
5 µm
5 µm
Pores
5 µm
Ni Percolation Threshold
• Allows feature extraction (Ni/ScSZ/Pores)
• FIBSEM, voxel sizes ~20-50nm
• 1350ºC sintering, 1 hr at temperature,
reduced
Ni Percolated
Fabrication and characterization of Ni/ScSZ cermet anodes for IT-SOFCs, Somalu MR, Yufit V, Cumming D, Lorente E, Brandon NP,
INTERNATIONAL JOURNAL OF HYDROGEN ENERGY, 2011, Vol:36, Pages:5557-5566.
Percolated nickel networks
Ni
30 Vol.%
A
Ni
40 Vol.%
Considered Ni
Percolation Threshold
Ni
50 Vol.%
Considered Ni Percolated
Considered Ni Percolated
Ni
5 µm
B
Ni
5 µm
C
5 µm
Preliminary results indicate:
• Ni30 – 65% of Ni is
percolated
• Ni40 – 97% of Ni is
percolated
• Ni50 – 90% of nickel is
percolated
Surface Area of particles in total volume analysed (x 103 m-1)
Ni
646
Ni
2481
Ni
1594
Pores
1317
Pores
2976
Pores
1999
ScSZ
1345
ScSZ
4195
ScSZ
2130
Advanced Analysis: 3D Interface Changes Ni30-Ni50
Ni
30 Vol.%
Ni
50 Vol.%
A
B
Ni
Ni
Pores
ScSZ
8 µm
Ni Percolation Threshold
Ni Percolated
•
•
•
•
•
•
Auriga Zeiss, 5kV, SEI, 1nA
100-200 Images
Feature extraction (Ni/ScSZ/Pores)
FIBSEM, voxel sizes ~20-30nm
1350ºC sintering, 2 hr at temperature
Ni 30% has some particles forming percolated
networks and other particles separate
• Ni content >30% is very well connected
Page 2
M.Samalu et al, Intl Journal of Hydrogen Energy 36(9),2011
Advanced Analysis of 3D Microstructure Changes
A
B
C
5 µm
D
E
10 µm
Example: Particles of Nickel
Page 4
Necks between adjacent particles :
Percolation, sintering and strain
3D imaging and quantification of interfaces in SOFC anodes, F. Tariq, M.Kishimoto, V.Yufit, G.Cui,
M.Somalu and N.Brandon (Journal of European Ceramic Society, In Press & Available May 2014)
3D Interfaces: Structure-property-behaviour
Experimental, Analytical and Modeling Results
Ni-Ni
6
ScSZ-ScSZ
2
4
2
0
Expt
Sim
1
1
0
0
Ratio
Expt
Sim
Neck
Ratio
N/A
Expt
Sim
Ratio
Experimentally Measured and Modelled
Ni30ScSZ
Ni50ScSZ
Ratio
Ni-Ni necks
(nm2/nm3)
2.7x10-4
3.55x10-4
1.32
Resistance:3.5
ScSZ-ScSZ necks
(nm2/nm3)
4.86x10-4
3.22x10-4
1.5
Ni-ScSZ necks
(nm2/nm3)
15.7x10-4
19.5x10-4
1.2
Page 15
Ni-ScSZ
2
Conductivity
Change
Expt. – 4
Sim. – 3.7
Most (though not
all) load is passed
through ceramic
matrix
Young's
Modulus
TPB
Density
For electrical conductivity
any contact (e.g. more
necks) would cause a larger
expt. conductivity increase
Expt. 1.4±0.1
Sim. - 1.1
Expt. - 1.1
Sim. – N/A
3D imaging and quantification of interfaces in SOFC anodes, F. Tariq, M.Kishimoto, V.Yufit, G.Cui,
M.Somalu and N.Brandon (Journal of European Ceramic Society, In Press & Available May 2014)
SOFC Tomography and Modelling
Unanswered Questions
Definition of Ni-YSZ Interface?
Self-Contact?
Fatigue/Cracking Behaviour?
Schematic from P.J.Withers, Adv. Eng.
Materials, 2011
Mechanisms at work
LSCF Electrode Imaging and Modelling
700°C
Porosity
2 µm
LSCF
Phases
Advanced 3D Imaging and
Analysis of SOFC Electrodes
F.Tariq, M.Kishimoto,
S.J Cooper, P.Shearing ,
N.P.Brandon, ECS Trans, 2013
Microstructural Analysis of an
LSCF Cathode using in-situ
tomography and simulation
S.J Cooper, M.Kishimoto, F.Tariq,
R.Bradley, A.Marquis,
N.P.Brandon, J.Kilner, P.Shearing
, ECS Trans, 2013
Flow Modelling in Porous structures
(Pa)
Higher pressure
Low pressure
Fluid Inlet
5 µm
- Pressure gradient calculated across
microstructure
- This can be used to calculate permeability
- A measure of how much fluid could pass
through this type of structure
Application of 3D imaging and analysis to the design of
improved current collectors for SOFCs
N Brandon, A Atkinson & Z Chen with Ceres Power
The core of the Ceres proposition is its unique metal-supported cell
AIR
•
Cathode Layer
Stainless Steel
Substrate
Thin steel substrate with even
thinner layers of active SOFC
materials coated on top
ELECTRICITY
FUEL
•
Low temperature electrolyte (ceria)
enables operation at <600 oC
•
Key advantages:
Ceria Electrolyte
Layer
Anode Layer
– Low cost cells
– Compact, lightweight design
– Mechanically tough
– Simple & reliable stack sealing
– Enables low cost balance of plant
© Ceres Power 2013
Title: 8th International Smart Hydrogen and Fuel Cell Conference
Rev: 1.0
10
Methodology
Simulation
Experiment
Indentation
experiment on
bulk/films/cells
Elastic
properties
Response curves
Fracture criteria prediction with
varied current collector designs
3D models with
different material
constitutives
3D models by
FIB/SEM
tomography
Indentation FEM
Compression FEM
Response curves
Elastic properties
Electrode structure
optimisation
Electrolyte failure
estimation
As FEM input parameters
Compare and validate the models
Axisymmetric modelling of mechanical
indentation into electrodes
Indentation process in axisymmetric modelling (a) before
indentation, (b) loading to a maximum depth, and (c)
complete unloading generated residual depth.
Nano-indentation curves for porous LSCF
cathodes
300
500
900°C_Experime
nt
Load (mN)
Load (mN)
400
1000°C_Experiment
1000°C_Simulation
250
300
200
100
200
150
100
50
0
0
0
800 1600 2400 3200 4000
Indentation depth (nm)
0
400
800
1200 1600
Indentation depth (nm)
2000
80
300
1100°C_Experim
ent
250
1200°C_Experiment
1200°C_Simulation
70
200
Load (mN)
Load (mN)
60
150
100
50
40
30
20
50
10
0
0
0
200
400
600
800
Indentation depth (nm)
1000
0
40
80
120
160
Indentation depth (nm)
Comparison of load vs. depth curves for models with varying porosities resulted from different
sintering temperatures. Porous LSCF sintered at different temps, 50 to 30 vol% porous, pellet,
spherical indenter, 25 mm radius, RT data
Results: elastic modulus and hardness
Comparison of elastic modulus and hardness results determined by experiment and simulation
Sintering
temperature
(°C)
900
1000
1100
1200
Method
Experiment
Simulation
Experiment
Simulation
Experiment
Simulation
Experiment
Simulation
hmax (nm)
4008.4
1973.4
950.1
164.1
Pmax (mN)
S (mN/nm)
a (nm)
437.9
1.05
13079.4
409.5
1.13
13146.3
241.4
0.89
9221.2
246.4
0.93
9256.5
252.2
1.02
6136.2
258.2
1.04
6137.0
67.5
0.86
2294.7
68.2
0.78
2241.1
E (GPa) H (GPa)
34.1
36.1
47.2
47.2
75.9
71.6
189.3
173.9
0.83
0.75
0.90
0.91
2.19
2.18
4.03
4.17
Electrode fabrication: porous scaffold
Tape casting or
screen printing
Porous CGO
Pore former
YSZ
Slurry
CGO
Mixture of commercial powder and nano-powder
(supplied by Prof Jawwad Darr, UCL)
YSZ
Co-sintering
T > 1300 C
State of the art electrodes: Impregnation of porous scaffolds
Porous
scaffold
Metal nitrate solution
Infiltration
550ºC, 1 h
+
heating & cooling
n times
Decomposition
To oxide
University of St Andrews
University of Pennsylvania
FIB-SEM: 1 x infiltration
After reduction
Before reduction
CGO
NiO
Ni
Enhanced triple phase boundary density in infiltrated electrodes for SOFCs, M Kishimoto, M Lomberg, E Ruiz-Trejo and N P Brandon, J Power
Sources, 2014, Vol:266, Pages:291-295..
3D reconstruction Ni x 1 -GDC
GDC
Ni
Ni-GDC
TPB
TPB (with GDC)
4.2 μm
Ni (with GDC)
Enhanced triple phase boundary density in infiltrated electrodes for SOFCs, M Kishimoto, M Lomberg, E Ruiz-Trejo and N P Brandon, J Power
Sources, 2014, Vol:266, Pages:291-295..
3D reconstruction Ni(10)-GDC
GDC
Ni
Ni-GDC
TPB
TPB (with GDC)
7.5 μm
Ni (with GDC)
Enhanced triple phase boundary density in infiltrated electrodes for SOFCs, M Kishimoto, M Lomberg, E Ruiz-Trejo and N P Brandon, J Power
Sources, 2014, Vol:266, Pages:291-295..
Quantification
Volume fraction
[%]
Particle/pore size
[μm]
TPB density
[μm/μm3]
GDC scaffold
Ni(1)-GDC
Ni(10)-GDC
Conventional
Ni-YSZ
Ni
GDC
0.00
57.1
1.29
56.9
19.8
60.2
25.3
25.1
Pore
42.9
41.8
20.1
49.6
Ni
GDC
Pore
N/A
0.844
0.667
0.102
0.748
0.594
0.354
0.706
0.300
1.38
0.730
1.74
N/A
11.0
18.4
2.49
Enhanced triple phase boundary density in infiltrated electrodes for SOFCs, M Kishimoto, M Lomberg, E Ruiz-Trejo and N P Brandon, J Power
Sources, 2014, Vol:266, Pages:291-295..
Electrolyte Supported Cell Fabrication and Testing
(Air)
(Fuel)
11mm
16mm
Working
Electrode (WE)
Counter
Electrode (CE)
Reference
Electrode (RE)
1mm
2M Ni(NO3)2
10-20μm
270μm
10-20μm
Electrolyte
20mm
• 20-80% H2
• 550-750˚C
Screen Printed GDC, sintered at 1350˚C
Commercial electrolyte, YSZ
Screen Printed commercial LSCF-GDC
Ni(NO3)2 decomposition at 500˚C
M Lomberg, E Ruiz-Trejo, G Offer and N P Brandon, Characterization of Ni-Infiltrated
26GDC Electrodes for Solid
Oxide Cell Applications, J Electrochem. Soc., 2014, accepted for publication
Impedance Spectroscopy Results
10 times Ni-infiltrated GDC electrode, P(H2)=0.5atm, 100k-0.1Hz, OCV
580oC
690oC
750oC
Fitting
-Z'' (cm2)
0.15
L1
R_hfi
0.10
2.5kHz
0.05
Element
3.4kHz
L1
0.00
R_hfi
R_h
CPE1-T
CPE1-P
0.00R_l
CPE2-T
CPE2-P
0.05
M Lomberg, E Ruiz-Trejo,
Oxide Cell Applications, J
R_l
CPE1
CPE2
0.6kHz
Freedom
Free(+)
Free(+)
Free(+)
Free(+)
Free(+)
Free(+)0.10
Free(+)
Free(+)
Data File:
Circuit Model File:
R_h
Value
1.9281E-07
1.271
0.24069
1.818
0.54251
0.092636
0.15
0.017949
2
0.59862
Z' (cm )
Error
N/A
N/A
N/A
N/A
N/A
N/A0.20
N/A
N/A
Error %
N/A
N/A
N/A
N/A
N/A
N/A
N/A
N/A
C:\Users\ml2610\Dropbox\PhD\Sync folders
from IC desk\3 On going\Experimental Da
ta\Experimental
10xNi-CGO-YSZ-LSCF-CGO\2
G Offer and N P Brandon,
Characterization of Ni-Infiltrated
4-01-2013\All data files\FRA data\high t
Electrochem.
Soc., 2014, accepted for publication
emperature_2.mdl
GDC Electrodes for Solid
27
Summary
•Progress continues to be made in the application and interpretation
of 3D imaging to understand SOFC electrodes structures, and how
these relate to performance.
•In the next 12 months we will be able to leverage new EPSRC
capital investments in imaging and characterisation tools and additive
manufacturing.
• Our ultimate ambition is to move towards a design led approach to
SOFC fabrication, and to develop in-silico accelerated ageing
methodologies, in order to optimise both performance and lifetime of
operating devices.
Acknowledgements
•3D imaging and analysis–Dr. Farid Tariq, Dr. Masashi Kishimoto, Dr
Khalil Rhazoui, Prof Claire Adjiman, Dr Qiong Cai (Surrey), Guansen
Cui, Sam Cooper, Dr. Paul Shearing (UCL), Prof. Peter Lee and Dr.
Dave Eastwood (Manchester).
•Scaffold electrodes– Dr Enrique Ruiz-Trejo, Dr Paul Boldrin, Marina
Lomberg, Zadariana Jamil, Prof Jawwad Darr (UCL).
•The EPSRC for funding.
•Current collector Project collaborators Ceres Power.