Simulation of oxygen diffusion process on electrical conductivity relaxation

Finite element method (FEM) simulations were carried out for modeling the electrical conductivity relaxation (ECR) process of a mixed ionic electronic conductor upon abrupt change of oxygen partial pressure. Oxygen diffusion pathway was simulated considering enhanced surface exchange rate on the current and voltage terminals formed on the specimen. The results suggested that the vacancy diffusion coefficient, D_{V, ECR}, obtained from ECR method appears to be dependent on vacancy concentration, δ, even though the true D_V is constant. The effects of the following parameters were investigated; degree of catalytic effect, surface reaction rate constant and sample dimension. Change in the sample dimension in a realistic range did not effectively suppress the modification of diffusion paths, and the change of apparent chemical diffusion coefficient, D_{chem, app}, was inevitable when surface reaction rate constant, k_chem, and D_chem are in the same range. The results of the FEM simulation were confirmed by ECR experiments with catalytic active (Pt) and inactive (Au) electrodes.