Effect of Acidity and Electronic Conductivity of Mixed Conductors on Oxygen Exchange Kinetics and Their Sensitivity to Surface Impurities

This study explores the relationship between mixedconducting oxide properties and the Smith acidity of added impurities in perovskite structures. Conductivity relaxation measurementswere performed on La0.6Sr0.4CoO3δ and La0.8Ca0.2CoO3δ, with selected impurities (SrO, CaO, Gd2O3, Al2O3, Ga2O3, and SiO2) introduced based on their Smith acidity. The temperature dependence of oxygen exchange kinetics was analyzed before and after impurity infiltration, and results were compared to prior studies on porous Pr0.1Ce0.9O2-δ. The findings indicate that host material properties directly interact with impurities, influencing the performance. Both La0.6Sr0.4CoO3δand La0.8Ca0.2CoO3-δexhibited similar impurity acidity dependencies; however, basic oxides did not enhance oxygen exchange for La0.6Sr0.4CoO3δ, while for La0.8Ca0.2CoO3-δ, SrO and CaO infiltration led to improved k values. This suggests that surface acidity differences between the host and the impurity dictate performance enhancement or degradation. Additionally, comparisons with Pr0.1Ce0.9O2-δreveal that electronic conductivity modulates the sensitivity of oxygen exchange kinetics to impurities, with lower conductivity increasing sensitivity and higher conductivity reducing it. These results suggest that materials with acidic surfaces and low electronic conductivity have greater potential for performance enhancement through impurity infiltration compared to state-of-the-art air electrode materials for solid oxide cell application.