Effects of Ca Substitution in Single-Phase Sr1-xCaxTi0.8Fe0.2O3-ẟ Oxygen Transport Membranes and in Dual-Phase Sr1-xCaxTi0.8Fe0.2O3-ẟ-Ce0.8Gd0.2O2 Membranes

Oxygen transport membranes (OTMs) have gained a lot of attention for their application in different innovative fields, but the development of new materials able to combine high oxygen permeability and good chemical stability is crucial to boost the exploitation of such membrane-based technologies. Perovskite oxides are widely studied as mixed ionic-electronic conductors for the realization of OTMs. In this article, we focus on _Sr1-xCa_xTi_0.8Fe_0.2O_3-ẟ (SCTF) perovskites and investigate the effect of Ca content on the A-site of the permeation properties, both in single-phase SCTF membranes and in dual-phase membranes obtained by combining SCTF and the ionic conductor Ce_0.8Gd_0.2O₂ (CGO). In single-phase samples, we observed that the substitution of 40% Ca preserves the permeation performances of the non-substituted SrTi_0.8Fe_0.2O_3-ẟ membrane while allowing for a substantial decrease in the sintering temperature, thus facilitating membrane manufacturing. In dual-phase membranes, the increase in the Ca content in the perovskite causes an increase in grain size. The permeation is, at least partially, controlled by the kinetics of the surface exchange reactions. This limitation can be overcome by the addition of an activation layer; however, the permeance of activated CGO-SCTF membranes still remains lower compared to the single-phase parent perovskitic membranes.