Influence of M cations on structural, thermal and electrical properties of new oxygen selective membranes based on SrCo0.95M0.05O3−δ perovskite

In this work, various M cations like Bi5+, Zr4+, Ce4+, Sc3+, La3+, Y3+, Al3+ and Zn2+ were incorporated into SrCoO3−δ (SC) lattices one by one via doping strategy to form a series of new SrCo0.95M0.05O3−δ (SCM) mixed oxides for membrane separation. In general, the M cations have significant effects on the crystal structure, electrical conductivity, sintering behavior and the oxygen permeability of the SCM membranes even though only 5% of Co ions are exchanged. The phase structure of SCMs in the air atmosphere is seemingly determined by the electron configuration in the outer orbits of M cation. In the current cases, the doping of M cation with d10 configuration results in 2H-hexagonal structure while that with p6 gives rise to a cubic perovskite or brownmillerite. The formation of cubic perovskite induced by M cation increases the electrical conductivity and the oxygen permeability by 1–2 orders of magnitude due to the high density of oxygen vacancy. In particular, disk-shaped perovskite SrCo0.95Sc0.05O3−δ membrane demonstrates the highest oxygen flux and theoretical analysis indicates that the oxygen permeation process is rate-determined by the surface reactions.