Oxygen Diffusion and Surface Exchange Coefficients of Porous La0.6Sr0.4Co0.2Fe0.8O3−δ Decorated with Co3O4 Nanoparticles

Abstract

This work presents a comparative study of the diffusion D c h e m and surface exchange coefficients k c h e m of porous La0.6Sr0.4Co0.2Fe0.8O3−δ (LSCF) and Co3O4 nanoparticles decorated LSCF electrodes. The study was carried out using the 3DT-EIS method, which combines Electrochemical Impedance Spectroscopy experiments with FIB-SEM tomography data through an adapted Transmission Line–Adler Lane Steele electrochemical model.A reduction of the polarization resistance of about 60% was measured for the Co3O4 decorated LSCF respect to the reference LSCF cathode, in air at 700 °C. The Co3O4 decoration was found to modify the ORR surface reaction limiting mechanism from O2 dissociation to O-ion incorporation, whereas the diffusion coefficient was not modified by the decoration, which represents a surface diffusion process for both electrodes. After the EIS measurements, the Co3O4 particles were almost no longer visible by Field-Emission SEM on the surface of the decorated sample, but signs that these particles play an active role in Sr Segregation were observed by STEM-EDS, in particular by concentrating the segregated SrO in the surroundings of the decorated particles.