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

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

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.

Overall : H2(g) + ½O2(g) -> H2O(g) Anode: H2(g) + O2- -> H2O(g) + 2e- Cathode: ½O2(g) + 2e- -> O2- Activation energy… Wikipedia

Polarization losses VNernst = -ΔG/2F F = Faraday’s constant Outline diff processes… bullet diff losses… VNernst = -ΔG/2F F = Faraday’s constant ΔG = Gibbs free energy for overall cell reaction Dr. Mumm UCSB 2006

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

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).

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

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

ESD Solid State Ionics 156 (2003) 1 – 13

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

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

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

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

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

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

X-ray Diffraction

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

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

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