Fundamental Studiesof SOFC Materials - National … Library/Research/Coal...Fundamental Studies of...

Fundamental Studies of SOFC Materials

Eric D. WachsmanUniversity of Florida - U.S. Department of Energy

High Temperature Electrochemistry CenterDepartment of Materials Science and Engineering

University of Florida

QuickTime™ and aGIF decompressor

are needed to see this picture. UF-DOE HiTEC

[email protected]://hitec.mse.ufl.edu

Determination of Electrochemical Performance and Thermo-Mechanical-Chemical Stability of SOFCs from Defect ModelingDOE SECA Contract No: DE-FC26-02NT41562DOE Project Manager: Travis Schultz•Advance the fundamental understanding of the continuum-level electrochemistry of oxide mixed ionic-electronic conductors.•Obtain fundamental constants required for implementing the continuum-level electrochemical model from experiment. •Extend the models to multilayer structures and incorporate microstructural effects.•Verify the models through experiment.•Develop a transient version of the continuum-level electrochemical model.•Obtain time constants for various transport processes from electrical impedance spectroscopy to examine the effects of transients on SOFC performance.•Develop and deliver software modules for incorporation of the continuum-level electrochemical model into SOFC failure analysis software used by NETL, PNNL, ORNL and the SECA industrial teams.

Electrocatalytically Active High Surface Area Cathodes for Low Temperature SOFCsDOE EE/FE Contract No: DE-FC26-03NT41959DOE Project Manager: Lane Wilson•Develop a fundamental understanding of heterogeneous electrocatalytic phenomena at the surface of ion conducting ceramics.•Fabricate high surface area SOFC cathodes with controlled microstructure and porosity.•Develop low ASR cathodes for low to intermediate temperature SOFCs.

UF - DOE High Temperature Electrochemistry CenterDOE Advanced Research, HiTEC Contract No: DE-AC05-76RL01830DOE Project Manager: Lane Wilson•Develop the fundamental understanding of ionic transport in, and electrocatalytic phenomena on the surface of, ion conducting materials, spanning the range from first-principles calculations and molecular dynamic simulations of ionic transport and gas-solid interactions to synthesis and characterization of novel ion conducting materials and electrocatalysts.

Highlights of:

Brouwer Region III2cOi

= ch

Brouwer Region Ice = 2cVO

20 15 10 5 0 5 108

6

4

2

0

VO••

h •

′ ′ O i

′ e

′ M A

Brouwer Region IIacD = 2cVO

Brouwer Region IIb

cD = ch

Intermediate-PO2 (model)

Low-PO2 (model) High-PO2 (model)

log

[ i ]

(m

-3)

DEFECT STRUCTURE DEFECT EQUILIBRIA

log PO2 (atm.)

Defect Concentration Dependence on:• Defect formation energy• Temperature• PO2 cV =

34

FUNDAMENTAL PROPERTIES

Kr

12PO2

− 14 +

A2

⎛ ⎝ ⎜

⎞ ⎠ ⎟

32

⎡

⎣

⎢ ⎢

⎤

⎦

⎥ ⎥

23

VO••

Defect Energetics and Mobility Based on:• Crystal structure• Cation radii• Cation polarizability• Cation oxidation state• Etc.

QuickTime™ and aTIFF (LZW) decompressor

are needed to see this picture.

Ebond = A

r m

EXTENSION OF MODEL TO THERMO-MECHANICAL PROPERTIES

− Br n

A, B, n and m are constants

Lattice constant, a, has linear relationship with cv

Therefore, r ~ a ~ cV

Thermal expansiona − a0

a0

= αΔT

Chemical expansiona − a0

a0

=θa0

cV

Thermo - chemical expansiona − a0

a0

= αΔT +θa0

cV

cV =34

Kr

12PO2

− 14 +

A2

⎛ ⎝ ⎜

⎞ ⎠ ⎟

32

⎡

⎣

⎢ ⎢

⎤

⎦

⎥ ⎥

23

0

5000

10000

15000

20000

25000

0 24 48 72 96 120 144

Heat up in air

Dry Argon

5% wet H2/N

2

50% wet H2/N

2

Wet H2

Dry H2

Cool down in H2

Decreasing pO2

Ther

mo-

Che

mic

al E

xpan

sion

Δl/l

o x 1

0-6

Time (hrs)

Thermo-Chemical Expansion of GDC


0 100

3 103

6 103

9 103

12 103

0 5 10 15 20 25-log( pO

2 ) /atm

Che

mic

al E

xpan

sion

Δl/l

o x 1

0-6

0 100

3 103

6 103

9 103

12 103

0 5 10 15 20 25Che

mic

al E

xpan

sion

Δl/l

o x 1

0-6

-log( pO2 ) /atm

Kr = 1072 m-9atm-0.5 [1]

A = 0 m-3

θ = 3.2 x 10-3 nm3 [2,3]

Undoped Ceria GDC

Δll0

= αΔTthermal{ +θ 3

4KR

12 PO2

−14 + 1

2A( )

32

⎛

⎝ ⎜

⎞

⎠ ⎟

23

chemical1 2 4 4 4 3 4 4 4

Kr = 1072 m-9atm-0.5 [1]

A = 2.5 x 1027 m-3

θ = 3.2 x 10-3 nm3 [2,3]

1. T. Kobayashi et al., Solid State Ionics, 126 (1999) 3492. D.J. Kim, J. Am. Ceram. Soc., 72 (1989) 14153. M. Mogensen et al., Solid State Ionics, 129 (2000) 63 4. K. Sasaki and J. Maier, Solid State Ionics, 134 (2000) 303


0 100

3 103

6 103

9 103

12 103

0 10 20 30 40 50-log( pO

2 ) /atm

Che

mic

al E

xpan

sion

Δl/l

o x 1

0-6

Kr = 1060 m-9atm-0.5 [4]

A = 4.4 x 1027 m-3

θ = 3.2 x 10-3 nm3 [2]

YSZ



Ybond = 1r0

d 2Edr2

⎛

⎝ ⎜ ⎜

⎞

⎠ ⎟ ⎟ r=r0

Ebond = A

r m − Br n


Lattice constant, a, has linear relationship with cv

Therefore, r ~ a ~ cV

1. D-J. Kim, J. Amer. Ceram. Soc. 72 (1989) 1415.2. M. Mogensen, N. Sammes, G. Tompsett, Solid State Ionics 129 (2000) 63

YY∗

≈ aa0

⎛

⎝ ⎜

⎞

⎠ ⎟ − δ+3( )

aa0

= θcV +1

Y ≈ Y∗ θcV +1( )− δ+3( )

δ is equivalent to:• n (if A is constant)• m (if B is constant)as oxygen vacancies are introduced


EXTENSION OF MODEL TO THERMO-MECHANICAL PROPERTIESExperimental Validation

PO 2= 0.22 atm

PO2=9.5x10-5 atm

PO2=1.8x10-17 atmPO

2=4.5x10-22 atmPO

2 =5.1x10 -25atm

A

B

C

D

E

F

PO 2= 0.22 atm

PO2=9.5x10-5 atm

PO2=1.8x10-17 atmPO

2=4.5x10-22 atmPO

2 =5.1x10 -25atm

A

B

C

D

E

F

PO 2= 0.22 atm

PO2=9.5x10-5 atm

PO2=1.8x10-17 atmPO

2=4.5x10-22 atmPO

2 =5.1x10 -25atm

A

B

C

D

E

F

P O2

Vacancies preserved by fast cooling

5oC/

min

Fast cool

800oC, 5 hr

Tem

p. o C

Time, hr

H2, H2/H2O,N2, Air

EXTENSION OF MODEL TO THERMO-MECHANICAL PROPERTIESExperimental Validation - Nanoindents and Microstructure

SEM image of surface after thermal etch. Average grain size ~12 µm.

20 μ m

1 µ m

Nanoindents

Size: ~0.6 µm

Depth: ~125 nm

•Effect of crystallographic orientation on elastic modulus and hardness evaluated statistically by applying many indents on grains of known orientation.

•In-plane anisotropy can be measured by changing the indent orientation.

EXTENSION OF MODEL TO THERMO-MECHANICAL PROPERTIESExperimental Validation - Nanoindents and Microstructure

SEM image of surface after thermal etch. Average grain size ~12 µm.

• 100 indents were applied on the sample, which covered 100 µm X 100 µm ( ~25 different grains)

Modulus: 218.35±11.12 GPa

Hardness: 9.00±0.73 Gpa

• The small variations imply that ceria is elastically isotropic.

20 μ m

1 µ m

Nanoindents

Size: ~0.6 µm

Depth: ~125 nm

experiment

Y,Effect of Oxygen Vacancy Population on Elastic Modulus of

Ceria(measured in air)

Y,

experiment

model

Y( PO2) ≈ Y∗ θcV (PO2

) +1( )− δ+3( )

Effect of Oxygen Vacancy Population on Elastic Modulus of


Y,

experimentmodel




) +1( )− δ+3( )

Y,

experiment


Gadolinia-Doped Ceria (GDC)

(measured in air)

Y,

experiment model


) +1( )− δ+3( )



(measured in air)

Y,

experiment model




) +1( )− δ+3( )

(measured in air)

Y,

experiment


Yttria-Stabilized Zirconia (YSZ)

(measured in air)

Y,

experimentmodel


) +1( )− δ+3( )

(measured in air)


Yttria-Stabilized Zirconia (YSZ)

Higher temperature and higher current will shift decrease in modulus to higher PO2

Y,Effect of Oxygen Vacancy Population on Elastic Modulus of

Ceria, GDC,YSZ


) +1( )− δ+3( )

Extend to Include Microstructural Effects:

Y(p) = Yp=0(1−p)r where p is porosity and r ≈ 2 for porous ceramics [1]

Y(PO2, p) = Y*(θcV(PO2)+1)-(δ+3)(1−p)r

1. A. S. Wagh, R. B. Poepel, J. P. Singh, J. Mat. Sci., 26 (1991) 3862.

EXTENSION OF MODEL TO THERMO-MECHANICAL PROPERTIESY,

Y(PO2) ≈ Y ∗ θ 3

4 KR

12 PO2

− 14 + 1

2 A( )32( )

23

chemical1 2 4 4 4 3 4 4 4

+1⎛

⎝

⎜ ⎜ ⎜

⎞

⎠

⎟ ⎟ ⎟

− δ +3( )

0 100

3 103

6 103

9 103

12 103

0 5 10 15 20 25-log( pO

2 ) /atm

Che

mic

al E

xpan

sion

Δl/l

o x 1

0-6

Δll0

= αΔTthermal{ + θ 3

4 KR

12 PO2

− 14 + 1

2 A( )32( )

23

chemical1 2 4 4 4 3 4 4 4

SAME!

1. D-J. Kim, J. Amer. Ceram. Soc. 72 (1989) 1415.2. M. Mogensen, N. Sammes, G. Tompsett, Solid State Ionics 129 (2000) 63

KR = Equilibrium constant for VO•• formation

A = Dopant concentration

θ = Empirical constant = 3.2 x 10-3 nm3 [1,2]

FUNDAMENTAL QUANTITATIVE DEFECT CONSTANTS

UF-DOE HiTEC

Thermodynamics of Oxides•Computational and experimental thermodynamicsof SOFC materials.

Calculated Zr-O phase diagram

Equilibrium constant for VO•• formation

OOX = VO

•• + 2e’ + 1/2O2

KR = [VO•• ] n2 PO2

0.5/[OOX]

KR


UF-DOE HiTEC

Computational Materials Thrust•Large-scale molecular dynamics simulations to elucidate the effects ionic radius and polarizability of on ionic conductivity, the structure of vacancy clusters, and the mechanisms of oxygen transport.•First principles, electronic structure simulations. Calculation of defect formation energy in oxides from first principles and thermodynamics. Study of oxygen reactions at surfaces and interfaces.

Ni-GDC GDC LSCF



Ebond = A

r m − Br n


θ = ?


Ni-GDC GDC LSCF

Ab-initio calculation of ZrO2 grain boundary and comparison with Z-contrast TEM image

Defect formation energiesas a function of PO2



VO••

VO•

VOx

Computational Materials Thrust•Large-scale molecular dynamics simulations to elucidate the effects ionic radius and polarizability of on ionic conductivity, the structure of vacancy clusters, and the mechanisms of oxygen transport.•First principles, electronic structure simulations. Calculation of defect formation energy in oxides from first principles and thermodynamics. Study of oxygen reactions at surfaces and interfaces.

UF-DOE HiTEC

θ = ?

log

[ i ]

(m

-3)

log PO2 (atm.)

High-PO2 (model)

FUNDAMENTAL PROPERTIES

Brouwer Region Ice = 2cVO

Brouwer Region IIacD = 2cVO

Brouwer Region IIbcD = ch

Brouwer Region III3cVA

+ 3cVB = ch

′ ′ ′ V A

′ e

VO••

′ M A

h •

Intermediate-PO2 (model)

Low-PO2 (model)

′ ′ ′ V B

20 15 10 5 0 515

10

5

0

Same approach being applied to perovskites• Defect equilibria already developed

DEFECT EQUILIBRIADEFECT STRUCTURE

LaFeO3: Rhombohedrally distorted perovskite

• Structural optimization in progress

UF-DOE HiTEC

Calculated Lattice Constants

a= 3.7822 Å c= 3.6493 Å

Cutoff Energy : 500 eVExchange-Correlation approximation: LDAK-POINT spacing: 2X2X2

CATHODE DEVELOPMENTOptimize Microstructure for:

• Activation Polarization– Electrocatalytic Activity

• Increase specific catalytic activity• Increase TPB• Dispersed catalyst

• Ohmic Polarization– Electronic vs. Ionic Transport

• Electronic conduction path• Ionic conduction path

• Concentration Polarization– Gas transport

• Graded porosity • Gas vs. solid state transport

OO× ↔ VO

•• + 2 ′ e + 12

O2

• Temperature programmed reaction (TPR) – Ramp temperature in reacting gas mixture to determine catalytic activity and

selectivity• Temperature programmed desorption (TPD)

– Ramp temperature in He to determine adsorbed species

CATHODE DEVELOPMENT - Electrocatalytic Activity

0

10

20

30

40

50

60

0 100 200 300 400 500 600 700 800

Con

cent

ratio

n (p

pm)

Temperature ( oC)

O2

NO

La2CuO

4 TPD

500 ppm NO and 1% O

2 adsorption

Lattice-O

Surface-O

NO used as probe molecule:

NO = 1/2N2 + 1/2O2vs.

O2 = O2

Set up for 18O2 probe moleculewith 16O oxide catalyst:

18O2 = 18O2 - phys-adsorbed

18O2 = 18O16O - scrambled product

18O2 = 16O2 - lattice oxygen

Kinetics of scrambled productformation indicative of chargetransfer reaction and surface exchange coefficient, ko


0

0.002

0.004

0.006

0.008

0.010

0.012

0 200 400 600 800TEMPERATURE (°C)

La2CuO

4-δ

LaFeO3-δ

LaCrO3-δ

LaMnO3-δ

LaCoO3-δLaNiO

3-δ

TPR of NO over partially reduced LaBO3-δ

Effect of B-site transition metal on catalytic activity:• Cations with partially filled d-orbitals (Co, Ni) more active

TPR of NO over La1-xSrxCo1-y(Ru/Fe)yO3-δ

• Ru most active


• Potential programmed reaction (PPR) – Ramp voltage in reacting gas mixture to determine catalytic activity and selectivity

• Potential programmed desorption (PPD) – Ramp voltage in He to determine adsorbed species

Electrodes

Current/Voltage

Capillary to Mass Spec

UF-DOE HiTEC

YSZ


16O2

18O2

Electrodes

Current/Voltage

Capillary to Mass Spec

UF-DOE HiTEC

YSZ


Include:• Electrode structure• Current-voltage behavior: io~ko, k = f(V)

16O2

18O2

OO× ↔ VO

•• + 2 ′ e + 12

O2

18O2

16O2

18O2

16O2

KR = ko/ko

18O16O16O2

I (A)

C. Xia, Y. Zhang, M. Liu, Appl. Phys. Lett., Vol. 82, No. 6, 10 February 2003

(LSM-YSZ)(LSM-GDC-LSCF)

(LSM-GDC)

Benchmark

CATHODE DEVELOPMENT - Electronic vs. Ionic Transport

Ag-ESBsAg-ESBvm



Relative size of ionic/electronic conducting phase• Same volume fractions• ESB particle size reduction

20

30

40

50

60

70

80

90

100

0 100 200 300 400 500 600 700 800 900 1000 1100 1200 1300 1400 1500

Particle Size (nm)

Cou

nt (%

of h

ighe

st)

Unsieved Sieved Vibratory-milled(7 day)

VMagglomerate

VM Sieved


0.04

0.05

0.06

0.07

0.08

0.09

0.1

0 20 40 60 80 100

Time (h)

ASR

( Ωcm

2 )Stability @ 650˚C (100h) in air

Ag-ESBs

Ag-ESBvm

ASR = 4.10x10-04t + 6.30x10-02

ASR = 1.91x10-05t + 4.78x10-02


Smaller ESB particle size increases stability

However, ASR still increases with time under current due to electromigration of Ag

New Cathode Materials - Pyrochlores

K. S.Lee, J. Solid state Chem. 131 (1997), 405

• High Electrical Conductivity ~103 Scm-1

• Metallic (increases with decreasing temperature)

QuickTime™ and aTIFF (Uncompressed) decompressor


T, °C

BRO7BRO7-ESB(56/44)

BRO7vm-ESB(44/56) BRO7vm-ESB

(56/44)



0.1

1

10

100BRO7s-ESBvm

BRO7vm-ESBvm

BRO7vm-ESBs


BRO7s

ESBvm

ESBs

BRO7vm

( ) ⎟⎟⎠

⎞⎜⎜⎝

⎛⋅

ε⋅

τ⋅−−= JLDq

kTPPPPc

c

c

c

4airOatmosatmosinterface eelectrolyt-cathodeO 22exp@,

JLDq

kTPPa

a

a

a ⋅ε

⋅τ

⋅−=2fuelHinterface eelectrolyt-anodeH 22 @,

JLDq

kTPPa

a

a

a ⋅ε

⋅τ

⋅+=2O@fuelHinterface eelectrolyt-anodeOH 22 ,

ANODE

tortuosity

gas diffusivity porosity

J.-W. Kim, A. Virkar, K.-Z. Fung, K. Mehta and S. Singhal, J. Electrochem. Soc., 146 (1999) 69-78S. Chan, K. Khor, Z. Xia, J. Power Sources, 93 (2001) 130

CATHODE

EXTEND MODEL TO INCLUDE MICROSTRUCTURAL EFFECTS

21

2O

2

0 1P

ccc

kTqK

V

eVJ −

=⎟⎠⎞

⎜⎝⎛ η

=exp

DEFECT CONCENTRATION

( ) ⎥⎦⎤

⎢⎣⎡

⎟⎠⎞

⎜⎝⎛ ηα−−−⎟

⎠⎞

⎜⎝⎛ αη= 10 kT

qkTqJJ expexp

ACTIVATION OVERPOTENTIAL

⎟⎟⎠

⎞⎜⎜⎝

⎛Φ−Φ

η−−−

⎟⎟⎠

⎞⎜⎜⎝

⎛Φ−Φ

η−−−

⋅

⎟⎟⎠

⎞⎜⎜⎝

⎛Φ−Φ

η−−

⎟⎟⎠

⎞⎜⎜⎝

⎛Φ−Φ

η−+=−Φ−Φ

extthVe

VAeV

extthVe

VAeV

V

B

extthVe

extthVeV

V

V

V

Bthext

uu

zcuc

uu

zcuc

qzTk

uu

uuz

cc

qzTk

L

L

1

1

1

1

00

lnln

POTENTIAL

•Electrochemical model (with pore diffusion incorporated) matches “Virkar”* model, but with less fitting parameters, (3 vs. 10)

•Fitting parameters: τa/Da (effective tortuosity anode), τc/Dc (effective tortuosity cathode) and io (exchange current density).

YSZ @ 800 °CLSM cathode (air)Ni-YSZ anode (H2/H2O)

*J.-W. Kim, A. Virkar, K.-Z. Fung, K. Mehta and S. Singhal, J. Electrochem. Soc., 146 (1999) 69-78

0

0.2

0.4

0.6

0.8

1

1.2

0 1 2 3 4 5 6

Vol

tage

(V)

Current Density (A/cm2)

τa/Da = τc/Dc = 104 s/m2

io = 0.1 A/cm2



0

0.2

0.4

0.6

0.8

1

0 0.5 1 1.5 2 2.5 3

Vol

tage

(V)



0

0.2

0.4

0.6

0.8

1

1.2

0 1 2 3 4 5 6

Vol

tage

(V)


GDC @ 800 °CLSM cathode (air)Ni-YSZ anode (H2/H2O)


io = 0.1 A/cm2


io = 0.1 A/cm2

I-V & power density curves can also be generated for mixed conducting materials:

•Electrolytes such as GDC (above)-Shows reduction in OCP and current density due to low ti at 800°C

•Cathodes such as LSF and LSCF (near future)


0

0.2

0.4

0.6

0.8

1

0

0.1

0.2

0.3

0.4

0.5

0.6

0 0.5 1 1.5 2 2.5 3

Vol

tage

(V)

Pow

er Density (W

/cm2)


0

0.2

0.4

0.6

0.8

1

0

0.4

0.8

1.2

1.6

0 5 10 15 20

Vol

tage

(V)

Pow

er Density (W

/cm2)



io = 0.1 A/cm2τa/Da = τc/Dc = 104 s/m2

io = 0.1 A/cm2

Model shows decrease in effective tortuosity (τ/D) can dramatically increases power density

GDC @ 800 °CLSM cathode (air)Ni-YSZ anode (H2/H2O)


10-1

100

101

102

103

104

105

10-1 101 103 105 107

300 oC400 oC500 oC600 oC

700 oC800 oC900 oC

-Z''

/ ohm

s

Frequency / Hz

2.0 X 10-5 atm

Artifacts minimized by nulling

Oxygen diffusion through through porous cathode (5.9 s)

Ionic conductivity through electrolyte grain boundary

Ionic conductivity in the bulk electrolyte

DECONVOLUTION OF CATHODE MECHANISM

Dissociation and surface diffusion of O-species on LSM to TPB (0.18 s)

Oxygen exchange at TPB (0.0001 s)

LSM/YSZ

Step # Process identity “x” inR ∝ pO2

XEa (eV) τ (s)

at 800 °C1

2

3

4

5

Ionic diffusion through electrolyte bulk.

~0Independent

1.101.05d

-

Ionic diffusion across electrolyte grain boundary.

~0Independent

1.041.16d

-

Migration and incorporation of O2- from TPB into YSZ.

~0Independenta

0.971.10a

1.13b

8.5 X 10-5

1.6 X 10-5a

Dissociation and surface diffusion of O-species on LSM.

-0.15-0.268a,c

1.21.61a

1.69b

0.180.016a

Gas diffusion through porous electrode.

-1.1-1.02a,c

∼0∼0a

5.90.16a

a) X. J. Chen et al. / Journal of Power Sources 123 (2003) 17b) Jiang et al. / J. of Electrochemical Society 147 (2000) 3195

c) Kim et al. / Solid State Ionics, 143 (2001) 379d) Guo, Maier / J. of Electrochemical Society 148 (2001) E121


0

500

1000

1500

2000

2500

0 500 1000 1500 2000 2500 3000

850 C950 C1100 C

Z' / Ω

450 C

850 °C 1100 °C950 °C

0.1

1

10

100

1000

104

0.1 1 10 100 1000 104 105 106 107

850 C950 C1100 C

Frequency / Hz

450 C

Microstructure/Impedance - LSCF Sintering Temperature Effect

5 µm 5 µm 5 µm

-Z”/Ω

-Z”/Ω

Highest temperature coarsens microstructure - multiple changes to impedancePowder supplied by NexTech


z

50 nm

x UF-DOE HiTEC

y

LSM

YSZ

Focused Ion Beam•Enables 3-D analysis of electrode microstructure

- Particle-size, pore-size, & distribution- Triple-phase boundary density- Tortuosity

QUANTIFYING MICROSTRUCTURE

Measure grain to interface line distance

LSM-YSZ Grain Interface

Pore-YSZ Interface

Sample shown is screen-printed LSM sintered at 1350° C

LSM

YSZ13 um

Total Grain Interface: 8.1 umTotal Pore Interface: 4.9 um

UF-DOE HiTEC

QUANTIFYING MICROSTRUCTUREAREA FRACTION

150 nm150 nm

150 nm 150 nm

By combining consecutive line analysis, area density analysis is achieved.

Percent of grain density per total area is current approach.

Example: 67% grain-to-interface density

Lg/Total: 64% Lg/Total: 71 %

Lg/Total: x % Lg/Total: x%

Lg/Total: x %

UF-DOE HiTEC

QUANTIFYING MICROSTRUCTUREAREA FRACTION

13 um

8 um

LSM

YSZTotal Grain Interface: 8.1 umTotal Pore Interface: 4.9 um

Measure grain and pore area

By analyzing over multiple evenly spaced slices, volume fraction can be determined.

Ex.: 89% Area GrainSample shown is

screen-printed LSM sintered at 1350° C

UF-DOE HiTEC

QUANTIFYING MICROSTRUCTUREVOLUME FRACTION

150 nm150 nm

150 nm 150 nm

By combining consecutive area analysis, a volume density analysis can be achieved.

Lg/Total: 71 % Lg/Total: x %

Lg/Total: x% Lg/Total: x %

UF-DOE HiTEC

QUANTIFYING MICROSTRUCTUREVOLUME FRACTION

Calculate triple phase boundary density

Triple-phase points

Sample shown is screen-printed LSM sintered at 1350° C

LSM

YSZ13 um

Triple Phase Points: 9

UF-DOE HiTEC

QUANTIFYING MICROSTRUCTURETRIPLE PHASE LINEDENSITY

150 nm150 nm

150 nm150 nm

By connecting all of the triple phase points, the interface lines can be determined in the sample.

LSM

YSZ13 um

Triple Phase Points: 9

UF-DOE HiTEC

QUANTIFYING MICROSTRUCTURETRIPLE PHASE LINEDENSITY

YSZ

LSM

LTPB

GDC

LSM LSCF

YSZ or GDC

ATPB

Butler-Volmer Equation: J = J0[exp(qαηact/kT) − exp(-q(1-α)ηact/kT)]

J0 = j0 x ATPB = LTPB x wTPB

LSM/YSZ wTPB ≈ Debye length


LSM/GDC, LSCF/YSZ, LSCF/GDC wTPB > Debye length

wTPB ≡ f(geometry, contact area, material property)

UF-DOE HiTEC

UF-DOE HiTEC

QuickTime™ and a decompressor


LSM (Nextech) on YSZ

Consecutive 50nm slices


Tortuosity

τ = zpath/zthickness

ACKNOWLEDGEMENTCollaborating Faculty:Dr. Kevin Jones - FIB/SEM CharacterizationDr.’s Susan Sinnott & Simon Philpott - Computational MaterialsDr. Fereshteh Ebrahimi - Mechanical PropertiesDr. Juan Nino - Novel Oxide Materials DevelopmentDr. Wolfgang Sigmund - Novel Synthesis & MicrostructuresDr. Hans Seifert - Materials ThermodynamicsDr. Xin Guo - Nano Ionics and Interfaces

Results by post-docs:Dr. Keith Duncan, Dr. Jiho Yoo & Dr. Heesung YoonResults by graduated students:Dr. Abhishek Jaiswall, Dr. Jun-Young Park, Dr. Jamie Rhodes, Dr. Sun-Ju Song, Dr. Keith Duncan, Terry Clites, Su-Ho Jung, Sai Boyapati, Naixiong JiangResults by current graduate students:Jeremiah Smith, Matthew Camaratta, Sean Bishop, Yanli Wang, Briggs White, Joshua Taylor, Vincenzo Esposito, Chiara Abate, Jin Soo Ahn, Aidhy Dilpuneet, Brian Blackburn, Chin-Tang Hu, Shobit Omar, Eric Armstrong, Martin VanAssche, Cynthia Chao, Eric Macam, Tak-keun Oh, Doh Won Jung, Dan Gostovic, Aijiie Chen, JianlinLi, Chris Woan, Guojing Zhang UF-DOE HiTEC

Date post:	27-Jun-2018
Category:	Documents
Upload:	nguyenanh
View:	225 times
Download:	0 times

Fundamental Studiesof SOFC Materials - National … Library/Research/Coal...Fundamental Studies of...

Documents