Effect of high-temperature ageing on (La,Sr)(Co,Fe)O3-δ cathodes in microtubular solid oxide fuel cells

Abstract

Microtubular solid oxide fuel cells with La0.6Sr0.4Co0.2Fe0.8O3-δ (LSCF) cathodes were aged in ambient air at temperatures ranging from 700 to 1000 °C for up to 700 h. Distribution of relaxation time analysis of electrochemical impedance spectroscopy (EIS) measurements indicated an increase in the cathode resistance with increasing ageing temperature up to 900 °C. The cells aged at 1000 °C were not measurable. The degradation did not result from microstructural changes, as shown by focused ion beam-scanning electron microscopy (FIB-SEM) 3D tomography that showed no significant changes at ageing temperatures ≤900 °C. On the other hand, the amount of segregated Sr, present both on LSCF surfaces and in Sr-rich particles, increased with increasing ageing temperature and correlated well with the increase in cathode resistance. Analysis of the EIS and microstructural data using the Alder-Lane-Steele model indicates that the Sr surface segregation increases cathode resistance via a decreased oxygen surface exchange rate.