Preparation of cathodes for thin film SOFCs |
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Authors: | P Charpentier P Fragnaud D M Schleich C Lunot E Gehain |
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Institution: | (1) Laboratoire de génie des matériaux, ISITEM, La Chantrerie, Rue Christian Pauc, BP 90604, F-44306 Nantes cedex 3, France;(2) GAZ DE FRANCE, Direction de la Recherche, 361, Avenue du Président Wilson, BP 33, 93211 La plaine St Denis Cedex, France |
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Abstract: | SOFCs are expected to become competitive devices for electrical power generation, but successful application is dependent
on decreasing working temperature from 1000 to 800 °C, without detrimental effects on resistance and on electrode processes.
This requires a reduction of the stabilized zirconia electrolyte thickness and an optimization of the electrodes, especially
the cathode, where losses are higher. Strontium doped lanthanum manganites are the most common materials tested as cathodes
for SOFCs working at high temperature (1000 °C). This cathode material presents high electronic and oxygen-ion conductivities,
a thermal expansion coefficient compatible with stabilized zirconia and good catalytic activity.
For thin film SOFC devices working at intermediate temperatures (less than 800°C), we have studied the optimization of this
type of cathode. Strontium doped lanthanum manganite has been deposited on yttria stabilized zirconia electrolyte substrates
by spray-pyrolysis and by RF sputtering. The electrode performances depend strongly on cathode microstructure, influenced
by processing conditions. With spray-pyrolysis processes, large porosity is expected. This is important for the supply of
oxygen, via O2 molecules through the pores to the triple phase boundaries, where the gas, the cathode and the electrolyte are in contact
and where oxygen reduction may occur. However, large porosity can have a nefaste effect on electronic conductivity. With RF
sputtering, denser films with higher electronic conductivity are obtained. But, in that case, the supply of oxygen occurs
via adsorbed O-atoms in a diffusion process through the cathode to the electrolyte. Spraypyrolysis and RF sputtering have
been compared relative to electrode properties.
Paper presented at the 4th Euroconference on Solid State Ionics, Renvyle, Galway, Ireland, Sept. 13–19, 1997 |
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