Catalysts in SOFC

1. Catalysts in SOFC Use of Raney Nickel in Infiltration at Anode Advisors: Professors Trumble and Slamovich

2. How SOFC Works Anode Reactions: H2 2H+ + 2e- 2H+ + O2- ion H20 Cathode Reaction: ½ O2 + 2e- O2- ion Reaction Products: (H20, CO2, H2, CO, etc.) and Heat

3. Catalysts at the Anode • Background research done with Pt, but too expensive • Current catalyst is Nickel • Compare $8000 per ton of Ni vs. $8000 per pound of Pt • Suggesting Raney Nickel infiltration as an alternative to current process • Raney Nickel is a form of nickel that can be spread in very fine dispersion, which makes it a more effective catalyst

4. Why Raney Nickel? Cosintering and reduction (Current) Ni Heated to 1400˚C in a reducing atmosphere NiO NiO ZrO2 ZrO2 Ry-Ni Ni/Al alloy Leached in caustic solution Infiltration with Ry-Ni and leaching (Suggested)

5. Experimental Approach • Casting the Aluminum Nickel alloy • Characterization • Sintering the YSZ preform • The infiltration experiment • Analysis • Leaching

6. Making the Alloy • Mixed 48 wt% Nickel with 52% Aluminum to make approximately a 1:1 ratio alloy of Al3Ni and Al3Ni2 • Melted Aluminum first at 660˚C • Added Nickel which created an exothermic reaction that grew ‘white hot’ • Cast melt in steel mold

7. Phase Diagram Courtesy of M.F. Singleton, J.L. Murray, and P. Nash, 1990

8. Alloy Characterization (Al)+Al3Ni (eutectic) porosity Al3Ni Al3Ni2

9. X-Ray Diffraction ~50% Al3Ni, 50%Al3Ni2

10. Making the Preform • Started with Zirconia granules of approximately 25-50 µm • Sintered at 1400˚C for 4 hours with ramps of 300˚C per hour • Shrinkage occurred due to high temperature • Concerns with intragranular porosity 200 µm

11. Infiltration Set up Cooling Apparatus Crucible Cast Alloy Alumina Beads TungstenShields YSZ Preform Cooling Apparatus Heating Element

12. Infiltration Process • Ramped the furnace at approximately 50˚C per minute to 1350˚C under vacuum • Held the sample at 1350˚ for 5 minutes then applied 1 atmosphere pressure of 5% Hydrogen/Argon gas • Kept under pressure upon cooling • Cooled at a high rate to minimize oxidation reaction

13. Infiltration Results • It worked!! • It did not infiltrate the YSZ disk fully • Redox reaction prevention appears to have worked well • Unanalyzed metallic impurities more plentiful in infiltrated disk Crucible Melted Ni/Al alloy Alumina Beads Infiltrated Zirconia

14. Infiltration Analysis • Infiltration occurred in individual granules • Chemical reaction occurred on the surface • High porosity even before leaching • Mostly due to metal shrinkage

15. Sem Images SEM Photograph at 500x

16. Leaching (metal) 25 Seconds 45 Seconds 5 Seconds 25 Seconds 45 Seconds 5 Seconds Used 10% NaOH solution at 50˚C when leaching

17. Leaching (infiltrated Ysz) 25 Seconds 45 Seconds 5 Seconds 25 Seconds 45 Seconds 5 Seconds Used 10% NaOH solution at 50˚C when leaching

18. Overall analysis • Infiltration on a macro and micro scale • Surface corrosion of granules shows how infiltration occurred • Impurities found in metal ceramic matrix • Further Research is expected • Visibly equal metal/ceramic matrix • High porosity

19. Future work • More analysis of the infiltration product • Use SEM images to determine what occurred during infiltration • Use chemical analysis and XRD to analyze impurities and infiltration products • Infiltrate preform with Ni/Al alloys of different compositions and process data • Use Raney Nickel in co-sintering processes • Use SEM to determine structure’s porosity • Test different compositions of Ni/Al alloy at different temperatures

20. Acknowledgements • Professor Trumble and Professor Slamovich • Patti Metcalf • Brad Allison • Dave Roberts • Jeffrey Redding • NSF Grant (DMR-9912195)

21. Questions? Thank you.