Perovskite-type oxides for high-temperature oxygen separation membranes

Abstract Oxygen permeation through dense ceramic membranes of perovskite-like SrCo 0.9− x Fe 0.1 Cr x O 3− δ ( x  = 0.01–0.05), Sr 1− x − y Ln x CoO 3− δ (Ln = La, Nd, Sm, Gd; x  = 0.30–0.35; y  = 0–0.10), SrCo 1− x Ti x O 3− δ ( x  = 0.05–0.20) and LaM 1− x Ni x O 3− δ (M = Ga, Co, Fe; x  = 0–0.6) was studied. The SrCoO 3− δ -based solid solutions with cubic perovskite structure were found to exhibit highest permeation fluxes compared to other membranes. However, high thermal expansion coefficients and interaction with gas species such as carbon dioxide may complicate the employment of SrCoO 3− δ membranes for oxygen separation membranes. Alternatively, the LaGa 1− x Ni x O 3− δ ( x  = 0.2–0.5) perovskites, having significant permeation fluxes as well as thermal expansion coefficients in the range of (10.8–11.6) × 10 −6  K −1 , were demonstrated to be suitable as membrane materials at oxygen pressures from 1 × 10 −2 to 2 × 10 4  Pa. Testing oxygen permeation at oxygen partial pressures of 1–60 atm showed that only oxides with a high oxygen deficiency such as SrCo 0.85 Ti 0.15 F 3− δ possess sufficient oxygen permeation fluxes. The oxygen permeability of perovskites on the basis of LaGaO 3 and LaCoO 3− δ was found to be negligible at oxygen pressures above 15 atm, caused by low oxygen vacancy concentration and ionic conductivity of such ceramic materials.