Investigation of BSCF Investigation of BSCF Cathode on GDC Electrolyte Cathode on GDC Electrolyte for Intermediate Temperature for Intermediate Temperature SOFCsSOFCs
Vann Brasher
Mentors: Dr. Daniel Mumm
Anh Duong
Sungrok Bang
The General OutlineThe General Outline
The SOFCSynthesis of SamplesTestingConclusion/Future Work
The SOFCThe SOFC
•Electrochemistry
½ O2 + 2 e- O2-
O2- + H2 H2O + 2 e-
•Conductivity Requirements
Electrolyte O-
Cathode/Anode e-
Solid State Ceramics
The SOFC
Fuel Cell Problems/Voltage Losses
Electrochemical Activation (Overpotential)
porosity
mixed conductivity Ohmic
thin layers/materials Mass Transport
gas flow system
The SOFCThe SOFC
•Purely Electronic Conducting Cathode (LSM)
•Triple Phase Boundary limitations
•Mixed Conduction (LSF, LSCF)
•Incompatible with YSZ!
Synthesis of SamplesSynthesis of Samples
GNP
Synthesis of SamplesSynthesis of Samples
B.5S.5CxF1-xO3-δ
X=.2,.5,.75 Pm3m cubic Red=Oxygen Green=A-site
Ba, Sr Blue=B-site
Co, Fe
Synthesis of Samples
Screen printing on isostatically pressed GDC
BSCF + binder 1cm2 symmetric
(both sides) calcine
+ fast, cheap
+ simulates industry
- inconsistant (ink, blades)
TestingTesting
X-Ray Diffraction Identification
XRD database
published XRD
Lattice parameter
Bragg’s Law Increase with Co Oxygen vacancy
XRD of BSCF major peak by molar cobalt content
0
500
1000
1500
2000
2500
31 31.5 32 32.5 33
2 theta (degrees)
Inte
nsi
ty (
CP
S)
0.2
0.5
0.75
TestingTesting
SEM imaging
Visual Characterization
Porosity Nano-Scale
Features Surface Area Uniformity
TestingTesting
Symmetric Cell Tests Impedance (10mV AC) from 350-550 °C DC voltage + Impedance from 600-750 °C V - iR = η
Impedance of BSCF 5528 at 500 C
-2.00E+00
0.00E+00
2.00E+00
4.00E+00
6.00E+00
8.00E+00
1.00E+01
1.20E+01
1.40E+01
0.00E+00 1.00E+01 2.00E+01 3.00E+01 4.00E+01 5.00E+01
Z real
-Z i
m
TestingTesting
BSCF5528
0.001
0.01
0.1
1
10
-0.05 0 0.05 0.1 0.15 0.2 0.25
Overpotential (V)
Cur
rent
(A/c
m2) 600C
650C
700C
750C
BSCF557525
0.001
0.01
0.1
1
10
-0.05 0 0.05 0.1 0.15 0.2 0.25
Overpotential (V)
Cur
rent
(A/c
m2) 600C
650C
700C
750C
ConclusionConclusion
Overpotential is a measure of losses due to electrochemical activity at the cathode.
BSCF557525 has lower overpotential better for applications in SOFC cathode.
Can be linked to lattice expansion. More oxygen vacancies, larger cations, etc.
Future WorkFuture Work
Screenprint with consistency and quality Achieve consistent Impedance data More samples, aim for repeatability Compare with other materials Analyze factors related to overpotential (i.e.
porosity, surface area) Full Cells?
Take it Away!Take it Away!
Fuel Cells are efficient & clean
Mixed Conductors make good Cathodes
Making & Testing Cells takes many steps!
Cobalt increases eletrochemical efficiency
Acknowledgements Acknowledgements
National Science Foundation
Dr. Mumm & Lab (Anh, Sungrok)
Said & UROP
