Bulk Oxygen Diffusion and Surface Exchange Limitations in La2−xSrxNi1-yFeyO4+δ

Abstract

The oxygen permeation flux through dense La 1.2 Sr 0.8 Ni 0.9 Fe 0.1 O 4+δ membranes with different thicknesses (0.8 and 1.2 mm) was measured versus oxygen partial pressure gradient in the temperature range of 800–1000 ∘ C. The calculated values of critical membrane thickness clearly indicated the change of rate-limiting step from bulk oxygen diffusion (T < 900 ∘ ) to surface exchange (T > 900 ∘ ). In contrast to the promising cathode material, such as oxygen-excessive La 1.5 Sr 0.5 Ni 0.6 Fe 0.4 O 4+δ , the oxygen-deficient La 1.2 Sr 0.8 Ni 0.9 Fe 0.1 O 4+δ showed similar values of surface exchange coefficients, while oxygen-ion conductivity possessed higher activation energy and was significantly lower in the intermediate temperature range.