Electrical conductivity of Ba-Sr-Co-Fe cathode material for SOFC

Pooja Sawant, A N Shirsat, S Varma, B N Wani, S R Bharadwaj

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Paper ID : 93

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overview …

Renewable Energy and Fuel Cells

Solid Oxide Fuel Cells

Cathode for SOFC

Synthesis

Characterization

Electrical Conductivity

Conclusions

Future Work

Acknowledgement

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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)

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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

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Requirements for Cathode material…

Gel-combustion (GC)

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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…

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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

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