Effects of Nb and Sn co-doping on the structure and properties of SrCoO3-δ oxygen transport membranes

The structure and oxygen permeability of SrCo0.9-xNb0.1SnxO3-delta (x = 0, 0.03, and 0.05) perovskite membranes were systematically investigated by co-doping the B-site of SrCoO3-delta oxide with Nb and Sn. Combined X-ray and neutron diffraction experiments showed that all materials crystallized in the tetragonal P4/mmm space group and that the crystal structures approached the ideal cubic perovskite structure with increasing Sn concentration. In addition, X-ray photoelectron spectra confirmed that Sn-doping increases the (Co, Nb, Sn)-O bond strengths. The impact of Sn-doping on the oxygen transport of dense SrCo0.9-xNb0.1SnxO3-delta membranes was also investigated, under air/He gradient, as a function of both temperature and membrane thickness. The results showed that the oxygen transport of SrCo0.9Nb0.1O3-delta is governed by oxygen ion diffusion, while the oxygen surface exchange reaction is the limiting process for the Sn-doped membranes, SrCo0.87Nb0.1Sn0.03O3-delta and SrCo0.85Nb0.1Sn0.05O3-delta.