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New advanced fuel cell technologies are moving towards high-temperature proton conductors (HTPCs) to meet environmental issues. Their elaboration remains a challenge and micro-computed tomography (µCT) is an innovative way to control their quality. NiO-BZY anodic supports of a protonic ceramic electrochemical cell (PCEC), elaborated by co-tape casting and co-sintered at 1350 °C, were coated with a BZY20 electrolyte layer by DC magnetron sputtering. The µCT allowed to observe defects inside the volume of these PCEC half-cells and to show their evolution after an annealing treatment at 1000 °C and reduction under hydrogen. This technique consists in obtaining a 3D reconstruction of all the cross-sectional images of the whole sample, slice by slice. This allows seeing inside the sample at any desired depth. The resolution of 0.35 µm is perfectly adapted to this type of problem considering the thickness of the different layers of the sample and the size of the defects. Defects were detected, and their interpretation was possible thanks to the 3D view, such as the phenomenon of NiO grain enlargement explaining defects in the electrolyte, the effect of NiO reduction, and finally, some anomalies due to the shaping process. Ways to anticipate these defects were then proposed.

International audience; BaZr 1-x M x O 3-d (M=Ce and/or Y) perovskite materials are good potential candidates for Protonic Ceramic Fuel Cell (PCFC) electrolyte due to their remarkable property of protonic conduction at intermediate temperature (400-600°C). Fabbri et al. have reported a protonic conductivity of 2.10-2 S.cm-1 at 600°C for BaCe 0.7 Zr 0.1 Y 0.2 O 3-d [1]. However, the synthesis of these materials requires high temperature (1500°C) by solid state reaction. The hydrothermal synthesis in supercritical water appears then as a way to synthetize perovskite materials at a temperature as low as 400°C. Furthermore, this process allows the formation of nanometric powder. Finally the continuous hydrothermal process offers many advantages such as: "soft-chemistry" route, low cost and sustainable elaboration.

Due to their low environmental impact, their high efficiency and their fuel flexibility, Solid Oxide Fuel Cells are studied for many years in order to supply electricity without fossil sources. The need of interconnect to create a stack (providing electrical connection between anode and cathode) and seal every single cell (having to avoid any contact between air and fuel) appears as a crucial point. Ferritic Stainless Steel (FSS) like Crofer22APU are considered as good candidates for interconnects. These chromia forming alloys have to be operational in the service conditions: 800°C in air (cathode side) and in humidified hydrogen (anode side). The performance of the interconnect stainless steels is then limited by the oxide scale formation, low electronic conductivity of this scale and eventual volatility of chromium oxide. Previous researches demonstrated than the corrosion behaviors of La2O3 and Y2O3-coated and uncoated FSS in air and in H2/10%H2O are completely different [1, 2]. In anode atmospheres, the corrosion rate is higher, the alloys tend to form whiskers-type oxide morphologies, the porosity of the oxide scale is increased and the diffusion of Fe and Mn in the scale is promoted. However, one of the main parameters in interpreting the differences in oxidation behavior between air and wet hydrogen is that both the oxygen partial pressure and the water vapour partial pressure are different. Thus, the goal of this fundamental study is to realize oxidation of uncoated and La2O3 and Y2O3-coated Crofer22APU and Fe30Cr in O2, O2/H2O and Ar/H2O at 800°C and to compare these results with previous results (in air and in H2/H2O) in order to determine the exact influence of water vapor and oxygen partial pressure on corrosion behavior. Kinetics were registered for 100 h at 800°C and the corrosion products were carefully analysed by SEM, EDX, XRD, SIMS.

National audience; Abstract - Interconnects are among the most critical parts for commercialization of SOFCs. They separate the fuel and oxidant gases and provide electric connection between the anode and cathode of adjacent cells. A Ni-based alloy, Haynes230 alloy, was evaluated in this work as a candidate material for SOFC interconnects application. During operation, a scale of chromia forms on Haynes230. Unfortunately, this scale can degrade the fuel cell performances. Thus, protective coatings are required to increase long-term stability. In this study, a nanometric layer made of reactive element oxide (La2O3, Nd2O3 and Y2O3) was applied on alloy surface by MOCVD. Perovskite oxides, such as LaCrO3, NdCrO3 and YCrO3, are then expected to grow during high temperature oxidation processes, because they present a good conductivity at 800°C in air. The first goal of this study was to perform experiments in air and in H2/10%H2O at 800°C in order to validate the coating influence. The second goal of this study was to determine the influence on oxidation resistance of a pre-oxidation on coated and uncoated Haynes230 at 1000°C for 2 hours in air under atmospheric pressure.

The need of interconnect to separate fuel and oxidant gasses and connect individual cells into electrical series in a SOFC stack appears as one of the most important point in fuel cell technology. Due to their high electrical and thermal conductivities, thermal expansion compatibility with the other cell components and low cost, Ferritic Stainless Steels (FSS) are now considered to be among the most promising candidate materials as interconnects in SOFC stacks. Despite the formation at 800°C of a protective chromia Cr2O3 scale, it can transform in presence of water vapour in volatile chromium species leading to the lost of its protectiveness and then the degradation of the fuel cell. A previous study [1] demonstrated that in air the application by Metal Organic Chemical vapour deposition (MOCVD) of a nanometric layer of reactive element oxides (La2O3, Y2O3) on FSS improved both the electrical conductivity and the oxidation resistance. The beneficial effect of this type of coating on FSS on oxidation resistance in H2/H2O (anode side) is not yet completely understood. So, the goal of this study is to realise reactive element oxide coating (La2O3, Y2O3) on differently FSS and performed oxidation tests in H2/10%H2O. The corrosion products were analysed after 100 hours ageing at 800°C by SEM, EDX, TEM, SIMS and XRD. The corrosion kinetic of the uncoated alloys in H2/10%H2O is slightly faster than in air. The application of a reactive element oxide coating improves the oxidation resistance but the parabolic rate law constant is slightly superior to those obtained in air. In H2/10%H2O, the morphologies of the oxide layers are very different from those observed in air but the oxide phases are almost unchanged.

International audience; The oxygen transport properties in (La0.8Sr0.2)(Mn1-yFey)O3±δ (LSMF) with various iron contents y = 0, 0.2, 0.5, 0.8 and 1 were determined by the IEDP technique. Both oxygen diffusion and surface exchange coefficients were found to be greater for y = 0.8 and 1 than those of LSM (y = 0). Moreover, for y ≤ 0.5, grain boundary diffusion was the rate limiting step especially at lower temperatures. Thus, in the LSMF perovskite materials, the oxygen diffusion via oxygen vacancies is enhanced by Fe. The LSMF electrical performances were measured by impedance spectroscopy. Compared to LSM and LSF (y = 1), porous LSMF cathodes with y = 0.2–0.8 exhibit poor electronic conductivity: Fe, by reducing the number of couples Mn3+/Mn4+, decreases the amount of available hopping sites, limiting the electrical conduction. For LSF, the charge disproportionation Fe3+/Fe5+ improves the electrical properties. In conclusion, only the LSMF compounds with y~1 or 0 can be considered as good cathode materials for SOFC applications