Etude de la durabilité de cellules d'électrolyse de la vapeur d'eau à haute température (influence des paramètres de fonctionnement)

Ce travail porte sur l analyse du comportement en durabilité d une cellule à oxydes solides en fonctionnement en mode Electrolyse de la vapeur d eau à Haute Température (EHT). Il s agit plus particulièrement d identifier les paramètres influant sur la durabilité de la cellule et de comprendre les mécanismes associés, de manière à établir le meilleur compromis durabilité-performance. Un premier axe de recherche correspond à la caractérisation électrochimique initiale de la mono-cellule choisie pour l étude, à savoir une cellule à électrode support de type LSFC/YDC/8YSZ/Ni-YSZ dont le comportement électrochimique est étudié sous diverses températures, conditions de gaz et densités de courant. Ensuite, la dégradation des performances est étudiée in situ par spectroscopie d impédance électrochimique et voltampérométrie lors de diverses études séquentielles par paliers de 200 heures. L influence du taux de conversion et de la densité de courant sur la dégradation des performances est ainsi analysée. Pour compléter cette étude, des analyses physico-chimiques et microstructurales post tests ont été réalisées sur des échantillons ayant fonctionné 1000 heures afin de faire le lien entre les modifications électrochimiques observées et les changements de structure et de composition des matériaux de cellule. Des hypothèses de mécanismes de dégradation ont ainsi pu être formulées.This work is dedicated to the study on the long term behavior of a solid oxide electrolysis cell (SOEC). More specifically, the target is to identify and understand the influence of main working parameters on the cell durability in order to find the best compromise between performances and durability. The initial part of this work is to characterize electrochemically the single cell selected for the study, that is to say a cathode supported cell of the type LSFC/YDC/8YSZ/Ni-YSZ at different gas conditions, temperature and current density. Then, the degradation of the cell performances has been studied by Electrochemical Impedance Spectroscopy (EIS) and voltamperometry (i-V) curves during sequential tests of 200h. The influence of the most important working parameters like the current density and the steam conversion has been analyzed. To complete this study, physico-chemical and microstructural analyses have been performed on cells that have been operated over 1000 hours, to make a link between electrochemical degradation observed on the cell and composition and structural changes of cell materials.BORDEAUX1-Bib.electronique (335229901) / SudocSudocFranceF

Electrochemical characterization of YSZ thick films deposited by dip-coating process

Yttria stabilized zirconia (YSZ, 8% Y2O3) thick films were coated on dense alumina substrates by a dip-coating process. The suspension was obtained by addition of a polymeric matrix in a stable suspension of commercial YSZ (Tosoh) powders dispersed in an azeotropic mixture MEK–EtOH. The suspension composition was improved by the addition of YSZ Tosoh particles encapsulated by zirconium alkoxide sol containing yttrium nitrate which are the precursors of the 8-YSZ oxide. This optimal formulation allowed preparing, via a dip-coating process, thick films which were, after thermal treatment, homogeneous, dense and crack-free. A specific method was performed to measure the electrical conductivity, i.e. to determine the ionic conductivity of the film: it uses the four-point probe technique combined with ac impedance spectroscopy. The good agreement between the classical two-electrode measurements performed on YSZ pellets and the four-electrode ones performed on YSZ films allows concluding that this method is relevant for characterizing the transport properties of thick films

Intermediate temperature SOFC single cell test using Nd1.95NiO4+δ as cathode

This work deals with SOFC single cell tests using neodymium nickelate Nd1.95NiO4+δ as cathode material. This MIEC oxide exhibits high values of both surface exchange coefficient (k) and oxygen diffusion coefficient (D*), as well as high electronic conductivity, which result in an enhanced electrochemical activity with respect to classical materials. The SOFC cells were fabricated from an anode-supported electrolyte half-cell provided by InDEC B.V. Corporation, with a 36mmdiameter. The Nd1.95NiO4+δ cathode was prepared as a two-stage electrode consisting of a thin interlayer of several hundred nanometers covered by a thicker layer of dozens microns. The Nd1.95NiO4+δ oxide powders were synthesized using different routes in order to reduce the final annealing temperature, and to subsequently obtain submicronic powders. I–V characteristics of the single cells were investigated under hydrogen–air conditions. The power densities versus current densities curves are reported and the results of impedance spectroscopy measurements performed under these operating conditions are discussed

Hydrogène

Ces mots écrits par Jules Vernes dès 187 4 dans son roman « L'.île mystérieuse », auguraient déjà de l'intérêt des scienti­fiques et de la société en général pour une nouvelle forme d'énergie « plus propre et plus vertueuse ». Aujourd'hui, environ 180 ans après l'invention de la pile à combustible par Sir W.Grove en 1839, les technologies actuelles de pro­duction, de distribution, de stockage et de conversion du di-hydrogène (Hz), nous permettent d'envisager l'utilisatiqo de ce gaz dans un grand nombre d'applications industrielle