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National audience; Solid Oxide Fuel Cells are electrochemical devices that convert the chemical energy contained in a fuel/oxidizer pair, generally H2/O2, into electrical energy. They received a great deal of attention due to their high electrical efficiency (60%), durability, low cost and flexibility in the choice of fuel.1 The main specificity of SOFCs is a high operating temperature between 700 °C and 1000 °C, dictated by the ionic conduction of yttrium stabilized zirconia (YSZ), the reference electrolyte. A recent study showed that a bi-layer electrolyte based on stabilized bismuth oxide and stabilized ceria has led to a significant improvement with a specific power density of ~1 W.cm-2 at 650 °C. 2 In 2013, devices capable of operating at 550 °C were even marketed, thus opening up new perspectives for ionic conductors derived from bismuth oxide, widely studied at UCCS 20 years ago. These materials present ionic conductivities several order of magnitude higher than YSZ but have been neglected in recent years due to their instability in a reducing atmosphere. As part of the BIBELOT grant (ANR-18-CE05-0001), which aims at finding new cathode materials for this type of device, we initially considered the development of a two-layer electrolyte Er0.5Bi1.5O3/ Gd0.1Ce0.9O1.95 (ESB/GDC). For the fabrication and deposition of the ESB on GDC, the ESB powder was synthesized at temperatures as low as 500 °C using wet chemical co-precipitation and sol-gel procedure in order to minimize the grain size and therefore obtain a dense ESB layer. We will present here the first results obtained by spin coating on a dense electrolyte of GDC of an ink prepared from this ESB powder. AcknowledgementCNRS, Ministère de l'Enseignement Supérieur et de la Recherche and Agence Nationale de la Recherche and BIBELOT ANR-18-CE05-0001 are acknowledged for funding.References[1] D. M. Bierschenk, J. R. Wilson and S. A. Barnett, Energy Environ. Sci., 2011, 4, 944–951.[2] E.D. Wachsman, K.T. Lee, Science, 334 (2011), 935-939.

International audience; Solid Oxide Fuel Cells (SOFC) have received great attention this decade due to their high electrical efficiency (60%), their durability, their low cost and their flexibility on the nature of the fuel used (hydrogen, methane,…).1 The reference electrolyte used in these cells is Zr1.92Y0.08O3.96 (YSZ). It is the ionic conductivity of this component that limits the temperature range above ~700 °C. However, the high operating temperature of SOFC can result in cost limitations and operating complexities. In order to decrease the operating temperature, a recent study has shown that by using a bilayered electrolyte, formed of erbium stabilized bismuth oxide (ESB) and gadolinium doped ceria (GDC), it is possible to drop the operating temperature down to 350 °C. The bilayered electrolyte has led to a significant improvement reveiling to a specific power density of ~1 W.cm-2 at 650 °C.2 This study focuses on the fabrication and deposition of thin and dense bilayer electrolytes ESB/GDC. GDC pellets were prepared and sintered at different temperatures. An optimized grain microstrucure and density was obtained at 1300 °C. In order to maximize the size of the ESB powder, the latter was synthesized at temperature as low as ~500 °C using wet chemical co-precipitation (ESB-cp) and sol-gel procedure (ESB-sg). Due to its high sinterability, the ESB-sg was used to prepare the ink and dense ESB layers deposited with the spin coater which were obtained at a sintering temperature of 900 °C. Scanning Electron Microscopy (SEM) and Energy-Dispersive X-ray spectroscopy (EDX) showed a good interface between the ESB and GDC layers. AcknowledgementsCNRS, Ministère de l'Enseignement Supérieur et de la Recherche and Agence Nationale de la Recherche and BIBELOT ANR-18-CE05-0001 are acknowledged for funding.References[1] D. M. Bierschenk, J. R. Wilson and S. A. Barnett, Energy Environ. Sci., 2011, 4, 944–951.[2] E.D. Wachsman, K.T. Lee, Science, 334 (2011), 935-939.

National audience; Les piles à oxyde solide haute température (HT-SOFC) sont généralement composées d’une cathode composite La0.8Sr0.2MnO3 (LSM)/YSZ, d’un électrolyte à base de zircone stabilisée à l’yttrium (YSZ) et d’un cermet nickel/YSZ à l’anode. En raison de la conductivité limitée de la zircone stabilisée, des températures de fonctionnement élevées (> 700 °C) sont nécessaires pour atteindre la mobilité ionique requise. Les difficultés d’élaboration de ces dispositifs sont à l’origine des efforts développés pour abaisser la température de fonctionnement. Le remplacement d’YSZ par de l’oxyde de bismuth stabilisé à l’erbium (ESB) dans le compartiment cathodique et par de la cérine stabilisée (GDC) dans le compartiment anodique, deux matériaux présentant des conductions ioniques bien supérieures à YSZ, a permis d’obtenir des gains de performances importants, atteignant des densités de puissance de ~1 W cm-2 à 650 °C [1]. A la suite de ces travaux, plusieurs groupes ont cherché à améliorer ce type de SOFC en optimisant la microstructure ou la fabrication de la cathode mais en gardant la composition utilisée pour les piles à combustible classiques, La0.8Sr0.2MnO3 [2]. Dans ce travail, nous nous intéressons au rôle de la teneur en strontium dans La1‑xSrxMnO3 sur la résistance spécifique de surface (ASR) d’électrodes composites LSM/ESB. Les compositions x = 0.15, 0.3, 0.4, 0.5, 0.6, 0.8 ont été évaluées pour déterminer l’influence de la structure, des propriétés de transport électronique ou encore du rapport Mn3+/4+. En utilisant la diffraction des rayons X, l’analyse thermogravimétrique et la spectroscopie de diffusion des ions de basse énergie (LEIS), nous avons démontré que, contrairement à ce qui est observé à haute température où la ségrégation de l’oxyde de strontium à la surface des électrodes est le processus de désactivation principal, à plus basse température, c’est l’oxydation de surface de LSM qui limite la dissociation de l’oxygène. L’activité catalytique des cathodes a été évaluée par spectroscopie d’impédance sur des cellules symétriques avec un électrolyte d’ESB. Nous avons ainsi pu mettre en évidence à 500 °C, par rapport à la composition classiquement utilisée, une diminution d’un facteur 2 de la résistance spécifique de surface avec pour composition La0.6Sr0.4MnO3, plus riche en strontium [3].RemerciementsCette étude a été menée grâce au soutien du Fonds Européen de Développement Régional (FEDER), du CNRS, de l’Université de Lille, de la Région Hauts de France, du Ministère de l'Enseignement Supérieur et de la Recherche et de l’Agence Nationale de la Recherche (BIBELOT ANR-18-CE05-0001).

International audience; Typical high temperature solid oxide fuel cells (HT-SOFC) use a La0.8Sr0.2MnO3 (LSM)/Zr1.92Y0.08O3.96 (YSZ) composite cathode on a YSZ electrolyte and a nickel/YSZ cermet anode. Due to the limited oxide conductivity of yttria stabilized zirconia, high temperatures (> 700 °C) are required in order to achieve sufficient ionic conduction. However, elevated temperatures come with significant engineering challenges motivating the long standing effort to decrease the operation temperature of SOFC. Substituting YSZ by erbium stabilized bismuth oxide (ESB) in the cathodic compartment and gadolinium doped ceria (GDC) at the anode, two much better ionic conductors, allow for a significant improvement leading to a specific power density of ~1 W cm-2 at 650 °C.1 Based on these results several groups optimized the microstructure or preparation of the cathode without changing the composition of the LSM.2 However, this stoichiometry was optimized for high temperature compatibility with YSZ and needed to be optimized as well for lower temperature.Here, we focused on the influence of the strontium content in La1-xSrxMnO3 on the area specific resistance (ASR) of composite LSM/ESB electrodes. Several compositions (x = 0.15, 0.3, 0.4, 0.5, 0.6, 0.8) were tested to investigate the influence of the structure, the electronic transport mechanism or the Mn3+/4+ ratio. Using X-ray diffraction, thermogravimetric analysis and Low Energy Ion Scattering spectroscopy (LEIS) we showed that, differently from the high temperature range, where surface segregation of SrO is the main deactivation process, at lower temperature it is the surface oxidation that inhibits the oxygen reduction efficiency of LSM. The catalytic activity of the cathodes was evaluated by Electrochemical Impedance Spectroscopy (EIS) on symmetric cells using an ESB electrolyte. We found a 2-fold decrease of the ASR at 500 °C when switching from La0.85Sr0.15MnO3, i.e. the high temperature optimized stoichiometry, to La0.6Sr0.4MnO3.3AcknowledgementsThe Fonds Européen de Développement Régional (FEDER), CNRS, Région Hauts de France, Ministère de l'Enseignement Supérieur et de la Recherche and Agence Nationale de la Recherche and BIBELOT ANR-18-CE05-0001 are acknowledged for funding.References[1]E.D. Wachsman, K.T. Lee, Science, 334 (2011), 935-939[2]J.W. Park, B.H. Yun, D.W. Joh, K.T. Lee, Electrochemical Society, 68(1) (2015), 957-96[3]M. Pajot, V. Duffort, E. Capoen, A.-S. Mamede, R.N. Vannier, J. Power Sources 450 (2020), 227649.

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