Engineering of oxygen pathways for better oxygen permeability in Cr-substituted Ba2In2O5 membranes

Ba2In2O5 is a mixed ionic-electronic conducting (MIEC) ceramic-based material offering a large number of oxygen vacancies to become an alternative material for oxygen separation membranes from gas mixtures or even a CO2 plasma. This material was selected as model system to deeper analyze the structure-property relations, while making use of a promising structure stability. In this study, partial substitution of In3+ by Cr3+ yielded single-phase Ba2In2-xCrxO5-d (x = 0, 0.2, 0.25). This forced an altered arrangement of the oxygen vacancies and a structural change from orthorhombic (Ibm2) to tetragonal (I4cm). The highest oxygen permeability of P(O2) = 1.4 ± 0.1 mL min−1·cm−2·mm at 1223 K among all tested samples was obtained for x = 0.2. A precise adjustment of the degree of oxygen vacancy ordering and the unit cell volume in this material reduced the activation energy EA and enhanced the self-diffusion coefficient D0 of the oxygen ions boosting the oxygen permeability as demonstrated by the superior oxygen permeability at lower temperatures (~1000 K), still reaching an oxygen permeability of P(O2) = 0.72 ± 0.04 mL min−1·cm−2·mm at 773 K. This concept seems plausible for an adaption to other structurally related membrane materials.