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Electrical conductivity of Ba-Sr-Co-Fe cathode material for SOFC
Pooja Sawant, A N Shirsat, S Varma, B N Wani, S R Bharadwaj
11/12/2013 1
Paper ID : 93
11/12/2013 2
overview …
Renewable Energy and Fuel Cells
Solid Oxide Fuel Cells
Cathode for SOFC
Synthesis
Characterization
Electrical Conductivity
Conclusions
Future Work
Acknowledgement
11/12/2013 3
Introduction to Fuel Cells …Renewables in energy production …
• Based on hydrogen technology• High efficiency, Low pollutant• Sustainable fuel resources• Energy-environment issues
Leading technology for future power generation Direct conversion of chemical energy into electrical energy Cleaner & Low Environmental Impact Fuels used are Renewable viz. landfill gas, Biomass based fuel, Hydrogen
Configuration of components in a fuel cell car
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State-of-the-art SOFC Materials
Electrolyte : Electrolyte is for oxygen ion conduction e.g. stabilizes zirconia Zr1-xYxO2x/2 (YSZ)
Anode : Hydrogen oxidation happens at anode e.g. Ni-YSZ
Cathode : Cathode works for the reduction of O2. e.g. La1-xSrxMnO3 (LSM)
5
Electron conductingGood porosityGood electrode kineticsMechanical & chemical compatibility with electrolyte
Ba0.5Sr0.5Co1-xFexO3−δ (BSCF) perovskite oxide was first reported as a potential IT-SOFC cathode material in 2004
System Studied… Ba0.5Sr0.5Co1−xFexO3−δ (BSCF) Compositions with respective labels
Compound Label
Ba0.5Sr0.5Co0.8Fe0.2O3-δ BSC8F2
Ba0.5Sr0.5Co0.6Fe0.4O3-δ BSC6F4
Ba0.5Sr0.5Co0.4Fe0.6O3-δ BSC4F6
Ba0.5Sr0.5Co0.2Fe0.8O3-δ BSC2F8
11/12/2013
Requirements for Cathode material…
Cation Complexation (CC)
IR (Å) IR (Å)
Co4+ 0.53 Fe4+ 0.58
Co3+ 0.61 Fe3+ 0.64
Co2+ 0.74 Fe2+ 0.78
Effective ionic radius (IR) for Co and Fe ions with different oxidation states
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Label System Lattice Parameters [Å] a
Cell Vol.[Å3]
Relative Density
(%)
Crystallite size (nm)
BSC8F2 Cubic 3.983 (1) 63.193 (37) 88 100
BSC6F4 Cubic 3.972 (1) 62.675 (29) 78 52
BSC4F6 Cubic 3.962 (1) 62.195 (11) 81 129
BSC2F8 Cubic 3.949 (1) 61.584 (16) 79 49
Label System Lattice Parameters [Å] a
Cell Vol.[Å3]
Relative Density
(%)
Crystallite size (nm)
BSC8F2 Cubic 3.981 (1) 63.110 (24) 85 140
BSC6F4 Cubic 3.973 (0) 62.717 (11) 81 147
BSC4F6 Cubic 3.965 (0) 62.340 (20) 82 150
BSC2F8 Cubic 3.953 (1) 61.795 (30) 80 152
Cell Parameters and relative density of BSCF compositions
Synthesized by gel combustion route
Synthesized by Cation complexation route
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A
Current Source Ammeter
l
Voltmeter
V
w
h
Electric conductivity measurement by four – probe method.Constant current (I) is supplied, voltage across the two points (separated by l ) with change in temperature measured. Resistance R= V/I
Conductivity σ = l / R × w ×h11/12/2013 9
Specific Conductivity σ, Scm-1 (at 723 K)
GC CC
BSC8F2 20.27 38.86
BSC6F4 18.73 33.04
BSC4F6 37.95 32.82
BSC2F8 25.64 31.91
GC CC
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Activation energy (eV) (400-700 K)
GC CC
BSC8F2 0.37 0.42
BSC6F4 0.33 0.39
BSC4F6 0.30 0.30
BSC2F8 0.27 0.27
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Weight loss (%)
GC CC
BSC8F2 1.41 1.01
BSC6F4 2.28 0.83
BSC4F6 2.28 0.95
BSC2F8 2.30 1.63
GC CC
Temperature dependence weight losses for 1273 K sintered BSCF compositions
Thermogravimetry analysis was carried out to relate the effect of Fe substitution in place of Co on conductivity behavior of BSCF series…
11/12/2013 12
Single phase cubic Ba0.5Sr0.5Co1−xFexO3−δ compositions were synthesized by gel-combustion and cation complexation routes.
As Co gets replaced by Fe, cell parameters decreased systematically. Electrical conductivity of BSCF samples initially increased with
temperature through a maximum and then decreased with further rise in temperature. This attributed to the loss of lattice oxygen.
Fe substitution has very little effect on overall electrical conductivity. But still, there is need to increase overall conductivity of BSCF compositions to get good performance cathode for current state-of-the art IT-SOFCs.
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Measurement of thermal expansion coefficient
Study of chemical compatibility with different electrolyte materials
Increase the electronic conductivity
Study composite cathode materials
Acknowledgement …
Dr. T. Mukherjee Dr. D. Das
Dr. S. R. Bharadwaj Dr. B. N. Wani
Dr. S. Varma Mr. A. N. Shirsat
Mr. Ganesh Mane Mr. Suhas Phaphale
All my collaborators, office staff and other people with whom I interacted during these works
BARC-Mumbai University Collaboration Scheme, DAE for financial grant
& providing a solid platform to carry out my research work
11/12/2013 15