Component interactions after long-term operation of an SOFC stack with LSM cathode

Abstract

The reliable long-term operation of stacks with a low degradation rate is a prerequisite for the commercialization of solid oxide fuel cell (SOFC) technology. A detailed post-test analysis of stacks is of major importance in understanding degradation mechanisms. Here the results are reported of a post-test analysis of an SOFC stack with anode supported cells with Ni/YSZ anode, 8YSZ electrolyte, and a lanthanum strontium manganite (LSM) cathode operated under steady-state conditions for 19,000 h. In particular, the microstructural and chemical analyses of the relevant metallic and ceramic components are reported. The interconnects were coated with a (Mn,Co,Fe) 3O 4 spinel by atmospheric plasma spraying, which prevented Cr evaporating into the cathode compartment. The diffusion of Mn from the (La,Sr)MnO 3 cathode into the 8YSZ electrolyte led to local enrichment at grain boundaries, which might have been responsible for the degradation via electronic pathways leading to partial short-circuiting across the electrolyte. However, the ultimate failure of the stack was the result of a weakening and fracture of the 8YSZ electrolyte along grain boundaries due to the local Mn enrichment.