Presentation of independent honors research thesis (June 2011) for Bachelor of Science in Materials Science & Engineering at Northwestern University.

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

7. + 6
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)

9. + 8
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

10. + 9
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

11. + 10
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

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Pechini vs. solid-state

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Redox Cycling

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Calcination temp XRD

15. + 14
Pechini Synthesis, Varying at.% Pd