Presentation of independent honors research thesis (June 2011) for Bachelor of Science in Materials Science & Engineering at Northwestern University.
Maiyalagan,Performance of carbon nanofiber supported pd ni catalysts for elec...
Pd-Substituted (La,Sr)CrO3 for Solid Oxide Fuel Cell Anodes
1. +
Pd-substituted (La,Sr)CrO3 Anodes
for Solid Oxide Fuel Cells
Emma Dutton
Materials Science & Engineering
Senior Honors Research Thesis
June 8, 2011
2. + 1
Acknowledgements
Professor Scott Barnett, PI
David Bierschenk Ph.D., Mentor
Dr. Kathleen Stair
The Barnett Lab Group
Jerry Carsello and the J.B. Cohen X-Ray Diffraction Facility
3. + 2
Solid Oxide Fuel Cells
Efficient chemical-to-electrical conversion at 500-1000 °C
with low pollutants
Commercialized stationary power generators with anodes
made of 8mol% Yittria-stabilized Zirconia with Ni catalyst
(Ni-YSZ)
Ni-YSZ problems: poisoned by fuel impurities, susceptible
to carbon build-up, ruined by redox cycling
4. + 3
Sr- and Pd-substituted LaCrO3
LaCrO3 perovskite structure
Easily doped to tailor properties
Stable, non-reactive at operating
temperature
Sr substitution on La sites for
increased ionic and electronic
conductivity
Pd substitution on Cr sites for
catalytic activity B. A. Boukamp, Nature Materials 2003, 2, 294-296.
“Catalyst-precipitating” anode
Pd nanoparticles exsolve from matrix La0.8Sr0.2Cr1- Pd O3-δ
onto surface, coarsening with time
Unique regenerative behavior upon “LSCrPd”
redox cycling
5. + 4
Experimental Design
Prior research shows better anode performance
than Ni-YSZ at 600 °C
Processing Property Performance
Synthesis method Structure Time-dependent Efficient
Solid State Rxn Phase purity resistance electrochemical
Pechini Method measured by measured by conversion at 600-800
Pd dopant levels powder X-Ray Electrochemical °C stable over long
20 wt% Diffraction (XRD) Impedance times (>200 hours)
8 wt% Spectroscopy
5 wt% (EIS)
How do synthesis method, phase purity, and Pd content affect
anode resistance at 600 °C?
6. + 5
Oxide Synthesis & Analysis
Solid state reaction uses oxide precursors
Mixed in organic solvent with wet ball-milling
Vacuum dried and calcined at 1000-1300 °C
Pechini sol-gel method uses nitrate precursors
Mixed with chelating agent to form gel
Heated to form resin and calcined at 1200 °C
Measure phase formation of the LSCrPd powders using XRD
Secondary phases complicate fuel cell performance
characterization, alter perovskite composition, possibly hinder
electrochemical processes
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Phase Formation Comparison:
Synthesis Method & Composition
LSCr95Pd05 with good phase purity, cannot compare
LSCr92Pd08 Pechini with better phase purity than solid-
state, evidence of La4PdO7 instead of La2Pd2O5
LSCr80Pd20 with similar phase purity for both synthesis methods but
different secondary phases
8. + 7
Anode Testing: Button Cells
Electrodes applied to electrolyte as inks in layers
Ag wires connect Au grids on electrodes to source meter
Electrochemical Impedance Spectroscopy (EIS)
Apply sinusoidal voltage at a range of frequencies and measure
current response at open circuit voltage (OCV)
Polarization resistance (Rp) - contribution from electrodes
Standard Rp deduction to account for cathode
LSCF-GDC LSCF
LSGM
LSCr
LSCrPd- La0.9Sr0.1Ga0.8Mg0.2O3-δ (LSGM)
GDC La0.6Sr0.4Co0.2Fe0.8O3-δ (LSCF)
Ce0.9Gd0.1O2-δ (GDC)
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Polarization Resistance Comparison
Best performance: Solid-state LSCr80Pd20 with Rp=0.3 Ω*cm2 after 20 hrs
Synthesis method: solid-state anodes with lower resistance overall
Pd content: response varies by synthesis method
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Conclusions
Synthesis method has an effect on phase formation
LSCr95Pd05 with good phase purity for both synthesis
methods, secondary phase content was too low to detect with XRD
LSCr92Pd08/Pechini with fewer secondary phases peaks than
LSCr92Pd08/Solid-state
LSCr80Pd20 with similar phase purity, but different secondary
phases and different anode behavior
Synthesis method changes microstructure with a clear effect on
anode resistance
Solid state synthesis: better performance overall, increased Pd
content is important factor for decreased anode resistance
Pechini synthesis: improved phase purity is important for decreased
anode resistance
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Synthesis method and phase purity
affect anode resistance
Pechini method
Nearly immediate increase in Rp
Improved phase purity = lower Rp
Solid state reaction – better anode performance
Stabilized anode resistance after 50 hours for 8 wt% Pd
Higher Pd doping = lower Rp