Oxygen transport kinetics affected by grain size – A permeation model study

Abstract

Grain size has obvious influence on the transport kinetics of oxygen species for mixed ionic-electronic conducting materials. Electrical conductivity relaxation and oxygen isotopic exchange with secondary ion mass spectrometry measurements cannot be used to determine the kinetic parameters at a steady state, while the permeation model study can give the kinetic parameters under real experimental steady states. Cobalt-free BaCe0.1Fe0.9O3-δ (BCF) membranes selected as an example with different grain sizes are studied by Zhu's model to disclose the influence of grain size on oxygen transport kinetics. The model is available for analyzing data of BCF membranes to obtain reasonable and exclusive oxygen diffusion and oxygen exchange kinetic parameters. The permeation flux of BCF membranes decreases with the increase of grain size. Model studies reveal that interfacial oxygen exchange resistances on both sides increase with the increase of grain size, while the bulk diffusion resistance changes slightly. It indicates that grain boundaries are active sites for oxygen exchange reactions and have little effect on the bulk diffusion.