Durability of LSCF-Coated Fe-Cr-Al Alloy for SOFC Applications

Abstract

The long-term durability of La0.6Sr0.4Co0.2Fe0.8O3 (LSCF)-coated Fe-Cr-Al alloy was investigated as a novel current collector material for SOFCs. The LSCF coating and subsequent heat-treatment at 700–900°C changed the microstructure of the surface oxide layer to a columnar structure of nanosize γ-Al2O3 arranged in the same direction, in which a small amount of Sr3Al2O6 contributes to the electronic conduction. The LSCF coating decreased the alloy oxidation rate by 23% at 700°C compared to the case without coating, following the parabolic growth law. Raising the temperature from 700°C to 900°C increased the oxidation rate of the LSCF-coated alloy by 51 times. The oxidation mechanism at 900°C was considered to be similar to that at 700°C, because of the similarity in microstructure, crystal structure, elemental composition and electrical conductivity. It was estimated that the Cr2O3 layer begins to grow on the inner side after roughly 6,000 h at 700°C, when the thickness of the surface oxide layer exceeds 1 μm. The same γ-Al2O3 columnar microstructure still covered the surface after 12,000 h. However, further improvement in durability and electrical conductivity is needed to meet the requirements for practical application.