Nanoscale Electrode Development for High-Temperature Fuel Cell Components

1. Nanoscale Electrode Development for Fundamental Studies of Mixed Ionic and Electronic Conductors as High Temperature Fuel Cell Components Jeevitha Evanjeline Martin Professor Daniel Mumm Grad Student: Anh Duong August 2nd, 2006

2. Outline • Solid Oxide Fuel Cell • Polarization losses • Triple Phase Boundary • Cathode microstructure • Traditional method for cathode fabrication • Experiment • Results • Discussion • Acknowledgements

3. Solid Oxide Fuel Cell • Solid-state device that uses an oxide-ion conducting ceramic material as the electrolyte. • The high operating temperatures eliminates the use of catalysts. • Oxygen is reduced at the cathode. • Oxygen ion is transported from the cathode to the anode through the electrolyte. • Forms Water. • Perfect candidate for hybrid systems.

4. Overall : H2(g) + ½O2(g) -> H2O(g) Anode: H2(g) + O2- -> H2O(g) + 2e- Cathode: ½O2(g) + 2e- -> O2- Wikipedia

5. Polarization losses • VNernst = -ΔG/2F • F = Faraday’s constant • ΔG = Gibbs free energy for overall cell reaction Dr. Mumm UCSB 2006

6. Importance of Porosity • Allows improved oxygen transport • Increases the TPB available for reaction • LSM (Lanthanum Strontium Manganate) • YSZ (Ytrria Stabilized Zirconia) Adler Chem Rev, 2004

7. Techniques used for the fabrication of Cathode layers • Traditionally GNP. • Glycine Nitrate Process. • Self sustaining combustion synthesis technique. • Produces fine homogeneous metal oxide powders. • Resulting ash is calcined to remove any organics. • Control over the stoichiometry. • Screen printing. • Now exploring: Electrostatic Spray Deposition (ESD).

8. Advantages of ESD • Recently developed. • Employs very fine precursor solution. • Allows the user to control porosity. • Flowrate • Voltage • Temperature • Time • Nozzle to substrate distance

9. Objective • To build ESD setup • To create porous Lanthanum Strontium Manganese Oxide(LSM) electrode layer over stainless steel substrate using Electrostatic Spray Deposition.

10. ESD Solid State Ionics 156 (2003) 1 – 13

11. Precursor solution needed for La0.8Sr0.2MnO3 • Lanthanum Nitrate (0.8) • Strontium Chloride hexahydrate (0.2) • Manganese Nitrate hexahydrate (1) • 33% Ethanol • 67% Butyl Carbitol

12. First try at making the solution • Lanthanum Nitrate • Strontium acetate • Manganese Nitrate + xH2O • Water • 33% Ethanol • 67% Butyl Carbitol NO!

13. Second try at making the solution • Lanthanum Nitrate • Strontium chloride hexahydrate • Manganese Nitrate hexahydrate • 33% Ethanol • 67% Butyl Carbitol NO!

14. Third try at making the solution • Lanthanum Nitrate • Strontium chloride hexahydrate • Manganese Nitrate hexahydrate • 3 drops of water • 33% Ethanol • 67% Butyl Carbitol YES!

15. Parameters for Experiments • Substrate = Stainless steel disk • Nozzle to substrate distance = variable • Voltage = 5kV • Flowrate = 0.5ml/h • Substrate temperature = 573K • Annealed at 1173K for 2hrs

16. Results a) Distance = 12mm c) Distance = 15mm b) Distance = 10 mm d) Distance = 19 mm

17. X-ray Diffraction

18. Discussion • Porosity increases with distance • X-ray Diffraction is compatible with known pattern except sample # 7 which showed contamination and cracks

19. Future work • Vary other parameters • Use YSZ as the substrate • Make layers of cathode while varying the density • Electrochemical characterization • Polarization curve • Impedance spectroscopy

20. Acknowledgements • IMSURE team • Dr. Mumm (ChEMS) • Anh Duong (ChEMS) • Professor Noo Li’s group • Gamma high voltage • National Science Foundation • Carl Zeiss center of excellence