Mixed ionic-electronic conductors (MIEC) such as rare-earth nickelates with a general formula Ln 2 NiO 4+δ (Ln=La, Pr, Nd) appear as potential cathodes for energy production and storage systems: fuel cells, Highlights High temperature/water pressure autoclave is used to study the reaction/corrosion at SOFC/HTSE electrode. High stability of Pr 2 NiO 4+δ (PNO) and Nd 2 NiO 4+ δ (NNO) dense ceramics vs. water pressure is demonstrated. Protonated rare-earth nickelates retain the perovskite-type structure and their H-content is determined. Very low laser illumination power is required to avoid RE nickelate phase transition. Nickelates show increasing stability from La to Pr/ Nd vs. CO 2-rich high temperature water vapour
During the last decades, perovskite-type oxides have received large attention as potential electrolytes and electrodes for Solid Oxide Fuel Cells (SOFC), including Proton Ceramic Fuel Cells (PCFC), gas separation membranes and High Temperature Steam Electrolysers (HTSE). A thermal treatment in an autoclave, at a temperature close to an operating temperature, was used to measure the chemical stability of La 0.6 Sr 0.4 Co 0.2 Fe 0.8 O 3 À δ (LSCF6428) ceramic under medium and high water pressure ( $20 and 40 bar). This mixed ionicÀ electronic conductor (MIEC) exhibits interesting properties as cathode of fuel cell materials. The reactivity rate of the investigated LSCF6428 sample under the protonation process conditions (several weeks at 550 1C using CO 2 -free and CO 2 -saturated water) was studied in order to evaluate a potential use of this compound. Bulk and surface structural/chemical changes were characterized by optical microscopy, TGA, dilatometry, Raman and ATR-FTIR spectroscopy. The results revealed only minor surface modifications in the case of ceramic treated under medium vapor pressure (20 bar) using CO 2 -free water. On the contrary, under higher pressure (40 bar) and CO 2 -saturated water several second phases were detected, namely strontianite, cobalt oxides and hematite. The chemical/structural stability of LSCF6428 is compared with previously investigated RareEarth nickelate ceramics: La 2 NiO 4 þ δ / Pr 2 NiO 4 þ δ / Nd 2 NiO 4 þ δ .
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