The influence of impurity ions on the permeation and oxygen reduction properties of Ba_0.5Sr_0.5Co_0.8Fe_0.2O_3-δ perovskite

This study aims to exploit the effects of little impurity ions on the properties and performance of Ba_0.5Sr_0.5Co_0.8Fe_0.2O_3-δ (BSCF) towards the development of membranes for oxygen separation and electrodes for oxygen reduction. The influences of impurity ions (Na⁺, K⁺, Mg²⁺, Ca²⁺, Cr^x+, Mn^x+, Si⁴⁺ and Cl^-) on the crystal structure, electrical conductivity, oxygen desorption/permeation behavior, sintering behavior and oxygen reduction activity of BSCF were systematically investigated. Rietveld refinements of the powder X-ray diffraction patterns revealed that most of the impurity ions, except Mg²⁺ and Si⁴⁺, can incorporate into the BSCF lattice without changing the lattice symmetry or forming new phases. The membrane containing the Mg²⁺ impurity exhibited a reduced grain size, whereas the membrane containing the Cl^- impurity exhibits poor sintering ability. The fluctuation in the oxygen permeation flux of the BSCF membranes could be correlated to their different sintering abilities and to the site doped with the impurity ions. The impedance spectra of symmetrical cells with BSCF electrodes containing various impurity ions showed that the small impurity ions did not strongly affect the electrode performance. These results suggested that low purity raw materials could be used to prepare BSCF materials, thus improving their economic attractiveness.