Influence of Mo-doping on structure and oxygen permeation properties of SrCo_0.8−xFe_0.2Mo_xO_3-Δ perovskite membranes for oxygen separation

The effect of cobalt substitution by highly charged Mo⁶⁺ cations in SrCo_0.8Fe_0.2O_3-δ (SCF) on the structure, microstructure, oxygen permeation performance and stability in the atmosphere containing carbon dioxide was systematically investigated by XRD, HT-XRD, Mossbauer spectroscopy, oxygen release technique and oxygen permeation experiments. The decrease in oxygen stoichiometry of SrCo_0.8-xFe_0.2Mo_xO_3-δ (SCFM) materials was accompanied by nanostructuring with observed formation of nanosized domains with ordered oxygen vacancies. Equilibrium “3−δ−lg pO₂−T” diagrams showed that SCF doping by molybdenum leads to broadening of the P₁ (cubic perovskite phase) stability region. The obtained SCFM membrane materials possess improved phase stability in the intermediate temperature range (T < 700 °C) and low oxygen partial pressure (pO₂ < 0.06 atm) compared to the undoped SCF oxide. The observed non-Arrhenius dependence of oxygen fluxes across SCFM disc membranes is related to combined control by bulk diffusion and surface exchange reactions.