A Fundamental Study on the Chemical Stability of La_(1-x)Sr_xCo_(0.2)Fe_(0.8)O_(3-δ) Cathodes for Intermediate Temperature Solid Oxide Fuel Cells

摘要

The chemical stability of La_(1-x)Sr_xCo_(0.2)Fe_(0.8)O_(3-δ) (x = 0, 0.4, 0.6, and 1) oxides before and after annealing at 750°C in air is investigated by field emission scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS), Auger electron spectroscopy (AES), and environmental transmission electron microscopy (TEM). Results indicate that Sr surface segregation has initially occurred at the sintering stage, and then, the secondary-phase particles are formed with increasing the heat-treatment time at 750°C in air. Increasing Sr content accelerates Sr segregation on the surface, because of two driving forces including interaction forces in the crystal lattice and thermal activation. AES and XPS results reveal that Sr and Co segregations toward the surface have great contributions to the chemical instability of La_(1-x)Sr_xCo_(1-y)Fe_yO_(3-δ) (LSCF) during annealing.