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

Abstract

This study explores the relationship between mixedconducting oxide properties and the Smith acidity of added impurities in perovskite structures. Conductivity relaxation measurementswere performed on La_0.6Sr_0.4CoO_3δ and La_0.8Ca_0.2CoO_3δ, 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 Pr_0.1Ce_0.9O_2-δ. The findings indicate that host material properties directly interact with impurities, influencing the performance. Both La_0.6Sr_0.4CoO_3δand La_0.8Ca_0.2CoO_3-δexhibited similar impurity acidity dependencies; however, basic oxides did not enhance oxygen exchange for La_0.6Sr_0.4CoO_3δ, while for La_0.8Ca_0.2CoO_3-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 Pr_0.1Ce_0.9O_2-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.