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Abstract
Design of materials for solid oxide fuel cells cathodes and oxygen separation membranes and studying their oxygen transport characteristics are important problems of modern hydrogen energy. In the current work, fundamentals of such materials design based on characterization of their oxygen mobility by oxygen isotope exchange with C18O2 and 18O2 in flow and closed reactors for samples of Ruddlesden – Popper-type oxides Ln2-xCaxNiO4+δ, perovskite-fluorite nanocomposites PrNi0.5Co0.5O3-δ – Ce0.9Y0.1O2-δ, etc. are presented. Fast oxygen transport was demonstrated for PNC – YDC (DO ~10-8 cm2/s at 700°C) nanocomposites due to domination of the fast diffusion channel involving oxygen of the fluorite phase with incorporated Pr cations and developed perovskite-fluorite interfaces. For LnCNO materials a high oxygen mobility (DO ~10-7 cm2/s at 700°C) provided by the cooperative mechanism of its migration was demonstrated. Depending on Ca dopant content and Ln cation nature, in some cases 1–2 additional channels of the slow diffusion appear due to decreasing the interstitial oxygen content and increasing the energy barrier for oxygen jumps due to cationic size effect. Optimized by the chemical composition and nanodomain structure materials of these types demonstrated a high performance as SOFC cathodes and functional layers in asymmetric supported oxygen separation membranes.
Highlights
Design of materials with mixed oxygen ion and electron conductivity (MIECs) for solid oxide fuel cells (SOFC) cathodes and catalytic membrane reactors for oxygen separation based on their oxygen transport characteristics is important problem of modern hydrogen
Undoped perovskites with a larger size of A-cation (e.g. Pr nickelates-cobaltites) are promising materials for SOFC and membrane applications due to stability to carbonization, compatibility with electrolytes and a high oxygen mobility and surface reactivity [4, 5, 8,9,10]
Optimized by the chemical composition and nanodomain structure materials of these types demonstrated a high performance as SOFC cathodes and functional layers in asymmetric supported oxygen separation membranes used for transformation of biofuels into syngas
Summary
For oxygen separation membranes’ materials a high mixed ionic-electronic conductivity is required to obtain a high oxygen flux across the membrane providing efficient performance in catalytic reactions of fuels selective oxidation into syngas [4, 5]. Conventional perovskite materials such as Sr-doped La manganites, ferrites-nickelates, ferrites-cobaltites have problems in their thermomechanical and chemical compatibility with electrolyte materials as well as chemical stability such as carbonization in CO2-rich atmospheres, which limit their application [1,2,3,4,5]. A high oxygen mobility of these materials (oxygen tracer diffusion coefficient ~10-7 cm2/s at 700°C) is provided by the cooperative mechanism of its migration involving both regular and highly mobile interstitial oxygen of perovskite and rock salt layers, respectively [5, 11,12,13,14,15,16,17]
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