Electrochemical Reaction Mechanism of LSM-YSZ Composite Cathode Based on 3D Simulation of Oxygen Diffusion and Oxygen Labeling Experiment

Abstract

Electrochemical reaction mechanism of an LSM-YSZ composite cathode is investigated using a combined measurement of oxygen labeling experiment and 3D microstructural reconstruction. First, oxygen isotope gas 18O2 was exposed to the LSM-YSZ cathode at 750 °C and a current density of 0.052 A/cm2. After 2 minutes of 18O2 supply, the gas was switched to water-cooled He to quench the cell and fix the incorporated isotope at the operating condition. After the oxygen labeling experiment, the cell piece was filled with an epoxy resin and polished to prepare the sample. Three-dimensional microstructure was obtained using a focused ion beam-scanning electron microscopy (FIB-SEM). Furthermore, between the measurement of the FIB-SEM, secondary ion mass spectroscopy (SIMS) analysis was conducted at the middle plane of the observed volume to correlate 18O distribution with the 3D microstructure. Based on percolation analysis of the microstructure, several isolated LSMs showed quite low 18O concentration, whereas some isolated LSMs showed 18O incorporation. For a further understanding of the correlation between the 18O distribution and microstructure, 3D numerical simulation using the reconstructed microstructure was carried out. First, potential distribution was obtained by solving gas diffusion and charge transportations which are coupled with the reaction at the reaction sites using the lattice Boltzmann method. Then, 18O distribution was predicted by solving oxygen diffusion along the calculated potential field. The electrochemical reaction mechanism was discussed by comparing the results of numerical simulation and experiment.