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-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.

Wikipedia

Overall : H2(g) + ½O2(g) -> H2O(g)

Anode: H2(g) + O2- -> H2O(g) + 2e-

Cathode: ½O2(g) + 2e- -> O2-

Polarization losses

•VNernst = -ΔG/2F•F = Faraday’s constant•ΔG = Gibbs free energy for overall cell reaction

Dr. Mumm UCSB 2006

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

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.

Solid State Ionics 156 (2003) 1 – 13

ESD

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

Second try at making the solution

Lanthanum Nitrate Strontium chloride hexahydrate Manganese Nitrate hexahydrate 33% Ethanol 67% Butyl Carbitol

Third try at making the solution

Lanthanum Nitrate Strontium chloride hexahydrate Manganese Nitrate hexahydrate 3 drops of water 33% Ethanol 67% Butyl Carbitol

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

a) Distance = 12mm

b) Distance = 10 mm

c) Distance = 15mm

d) Distance = 19 mm

Results

0

10000

20000

30000

40000

50000

20 30 40 50 60 70 80 90

2 Theta

Intensity

Sample 3

Sample 4Sample 5

Sample 7J CPDS

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

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