Evaluation of La_0.6Sr_0.4Co_0.2Fe_0.8O₃-Gd_0.1Ce_0.9O_1.95 composite cathode with three dimensional microstructure reconstruction

In the present study, the polarization characteristics of La_0.6Sr_0.4Co_0.2Fe_0.8O₃(LSCF) - Gd_0.1Ce_0.9O_1.95(GDC) composite cathodes with different volume ratios were investigated. Samples with volume ratios of 20:80, 30:70, 50:50, 70:30 and 100:0 vol % were tested. The electrochemical impedance spectroscopy tests and current voltage curve measurements were carried out for the current densities from 0 to 0.2 Acm⁻²with an interval of 0.05 Acm⁻². The results showed that a volume ratio of LSCF:GDC = 30:70 composite cathode led to the lowest overpotential, and the overpotential increased in the order of 30:70, 50:50, 70:30, 100:0, 20:80 vol %. Three dimensional microstructures of composite cathodes were reconstructed and quantified by dual beam focused ion beam-scanning electron microscope (FIB-SEM). The results showed that neither LSCF surface area nor triple phase boundary (TPB) alone could explain the dependence of polarization characteristics on volume ratios. Current and electrochemical potential distributions were simulated by the Lattice Boltzmann method, in which both surface and TPB reactions were considered. Prediction considering both surface and TPB reactions could predict qualitatively the dependence of overpotentials on LSCF - GDC cathode composition.