Impact of Ni and Mo Substitution on Oxygen Permeability and Electrical Conductivity in BaCo0.4Fe0.4Y0.2O3-δ Perovskite Oxides

Mixed ionic–electronic conducting (MIEC) perovskite oxides are good choices for air electrodes of solid oxide fuel cells (SOFCs), proton-conducting ceramic fuel cells (PCFCs), and/or oxygen permeation membranes. The composition of BaCo_0.4Fe_0.4Zr_0.1Y_0.1O_3-δ (BCFZrY) and its modified variants reveal encouraging results for air electrodes of both SOFCs and PCFCs. To further tailor the MIEC properties of the BCFY series, this study focuses on BaCo_0.4Fe_0.4Ni_0.1Y_0.1O_3-δ (BCFNiY) and BaCo_0.4Fe_0.4Mo_0.1Y_0.1O_3-δ (BCFMoY). These compositions were prepared through the citrate-based liquid mixing method. X-ray powder diffraction and corresponding Rietveld refinement studies confirm that the main phase is a cubic perovskite structure, although a secondary phase of <10 wt % appears in both compositions. At 800 °C, the total conductivities of BCFNiY and BCFMoY are 5.90 and 4.88 S cm^–1, respectively. The impressive total conductivity of BCFNiY is higher than that of the promising cathode BCFZrY. At the same temperature, the oxygen permeabilities of BCFNiY and BCFMoY are 0.44 and 0.29 μmol cm^–2 s^–1, respectively. The significantly higher oxygen permeability of BCFNiY compared to that of BCFMoY can be attributed to its lower absolute value of average bond energy (ABE), larger critical radius (r_c), and increased lattice-free volume (LFV). These factors collectively facilitate oxide-ion conduction and contribute to the enhanced oxygen permeation properties of the Ni-substituted composition. These results highlight BCFNiY as a promising MIEC perovskite for oxygen permeation membranes and air electrodes in next-generation SOFCs and PCFCs.