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Elaboration, caractérisation et modélisation de cathode sérigraphiée, La0.8Sr0.2MnO3, pour pile à combustible SOFC

Abstract : The properties of LSM screen-printed cathodes on YSZ electrolytes and the modelling of oxygen reduction have been studied.
A bibliographic review of published works on LSM and LSM/YSZ interface reveals the lack of consensus over the mechanism proposed between oxygen and LSM. The different theoretic models possible and their associated kinetic laws are presented to serve as the basis for the
kinetic modelling.
Microstructural characterisations proved the adaptability of the screen-printing technique for making electrodes. The layers are stable in time and well reproducible. Their microstructure is homogenous and regular with a porosity of 0.6.
Physico-chemical characterisations were carried out. Infra-red spectrometry analysis and thermo-programmed desorptions have shown the existence of different kinds of oxygen adsorbed species on LSM powder. A calorimetric study has revealed a change in the quantity of heat released during oxygen adsorption as a function of temperature. By XPS analysis on screen printed layers, important strontium segregation was observed depending on pressure, temperature and polarisation conditions.
From electrochemical characterisations made by impedance spectroscopy, three resistive contributions have been identified. Only the low frequency contribution, which is the only pressure sensitive contribution, was considered to correspond to an electrode phenomenon. Following a methodical study of the different modelling hypothesis, a mechanism for the cathodic reaction was obtained. The proposed model is complex. It is composed of three conductivity paths running in parallel (two surface paths and one bulk path). These paths involve two different oxygen species and their preponderance depends on pressure, temperature and polarisation conditions.
A study of water vapour influence completes this work, to understand its impact on the cathode electrical performance. The benefits brought by water vapour are not linked to a direct catalytic effect, as it does not affect the apparent activation energy of the cathode's process. The experiments seem to indicate that the benefits are linked to the strontium segregation at the surface of grains. It seems water vapour helps maintain and regenerate the initial properties of the layer.
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Submitted on : Wednesday, July 25, 2007 - 9:43:07 AM
Last modification on : Wednesday, June 24, 2020 - 4:18:31 PM
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  • HAL Id : tel-00165173, version 1

Citation

Noémie Caillol. Elaboration, caractérisation et modélisation de cathode sérigraphiée, La0.8Sr0.2MnO3, pour pile à combustible SOFC. Génie des procédés. Ecole Nationale Supérieure des Mines de Saint-Etienne, 2006. Français. ⟨tel-00165173⟩

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