A comparative study of the performance of SrCo_0.76 Fe _0.19 Al_0.1 O_x and (SrCo_0.8 Fe _0.2 O_3-δ)_0.95(SrAl₂ O ₄)_0.05 mixed-conducting membranes

Dense oxygen permeable ceramic membranes are promising materials for separating oxygen from air and for syngas production. The crystal structure, oxygen vacancy, microstructure, thermal expansion behavior, electrical conductivity, and oxygen permeability of two mixed-conducting ceramics: 5 mol% SrAl₂O₄-doped SrCo_0.8Fe_0.2O _3-δ (SCF-SA) and SrCo_0.76Fe_0.19Al _0.1O_x (SCFA), with the same overall cation composition, were systematically investigated in this work. The main phases of SCFA and SCF-SA are cubic perovskite and no orthorhombic brownmillerite appears from 700°C to 900°C in air, while SCF-SA presents minor unidentified phases. SCF-SA shows lower electrical conductivity than SCFA. SCFA membranes exhibit lower oxygen permeation flux than SCF-SA. At 850°C, the oxygen permeation fluxes of SCFA and SCF-SA are 1.23 and 1.46 mL/cm²/min, respectively, under the oxygen partial pressure gradient of 0.21 × 10⁵/1 × 10² Pa.