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This study concerns energetics of formation and the stability in high water partial pressure of BaLnCo2O6−δ, (Ln = La, Pr, Nd, and Gd) (BLnC) and BaGd1−xLaxCo2O6−δ, where x = 0.2, 0.5, and 0.7 (BGLC) double perovskite cobaltites. Those materials are extensively studied due to their potential applications as a positrode in electrochemical devices. Therefore, their stability under such conditions is a key issue. All investigated materials are thermodynamically stable relative to binary oxides and exhibit strongly exothermic enthalpies of formation. Moreover, BaGd0.3La0.7Co2O6−δ and BaGd0.8La0.2Co2O6−δ remain the main perovskite structure up to 3 bars of water vapor at 400 °C. At higher steam pressure, reaching 10 bar at 300 °C, the partial decomposition to constituent oxides and hydroxides was observed. The BGLC compounds exhibit higher negative formation enthalpies in comparison to single-Ln compositions, which does not translate into higher chemical stability under high steam pressures since the BLnC series retained the main perovskite structure at higher temperatures as well as in higher water vapor pressures. [ABSTRACT FROM AUTHOR]

This work addresses the thermochemical stability of ceramic materials –typically used in oxygen transport membranes– under the harsh gas environments found in oxyfuel combustion processes. Specifically, a dual-phase NiFe 2 O 4 -Ce 0.8 Tb 0.2 O 2-δ (NFO-CTO) composite and a single-phase La 0.6 Sr 0.4 Co 0.2 Fe 0.8 O 3-δ (LSCF) were studied. The effect of the main contaminants present in this kind of processes (CO 2 , SO 2 and H 2 O) has been tested. NFO-CTO composite remains stable under all the conditions studied whereas LSCF presents a poor stability in the presence of CO 2 and SO 2 . Regardless of the treatment, NFO-CTO conserves its crystalline structure, without giving rise to new species due to segregation or incorporation of sulphur and/or carbon. On the contrary, LSCF is prone to degradation in contact with CO 2 and SO 2 , segregating Sr in the form of SrCO 3 and SrSO 4 and Co and Fe in the form of CoO and Fe 3 O 4 . It is also shown that SO 2 interaction with LSCF is stronger than in the case of CO 2 . A concentration of just 2000 ppm of SO 2 in CO 2 is enough to subdue the formation of SrCO 3 , promoting the segregation of Sr only in the form of SrSO 4 . With the results presented in this work, it is possible to conclude that the NFO-CTO is a suitable candidate from the thermochemical viewpoint to be used as membrane material in 4-end modules for oxygen generation integrated into oxyfuel combustion processes whereas the use of LSCF should be dismissed. [ABSTRACT FROM AUTHOR]