Effects of La_0.8Sr_0.2Mn(Fe)O_3-δ protective coatings on SOFC metallic interconnects

SUS430 (16%-17% (mass fraction) Cr) can be used as interconnects for solid oxide fuel cells (SOFCs) that operate at lower temperatures (< 800°C). However, oxidation of steel can occur readily at elevated temperatures leading to the formation of Cr₂O₃ and spinel (Fe₃O₄) and thus greatly degrades the performance of the fuel cell. The aim of this work was to reduce oxide growth, in particular, the Cr₂O₃ phase, through the application of La_0.8Sr_0.2MnO_3-δ (LSM20) and La_0.8Sr_0.2FeO_3-δ (LSF20) coatings by atmospheric plasma spraying technology (APS). Oxide growth was characterized by using X-ray diffraction (XRD), scanning electron microscopy (SEM) with an energy dispersive X-ray (EDX) analyzer. During oxidation of fifty 20 h cycles at 800°C in air, the samples with coatings remained very stable, whereas significant spallation and weight loss were observed for the uncoated steel. LSF20 presents apparently advantages in reducing oxidation growth, interface resistance and inhibition of diffusion of chromium. After exposure in air at 800°C for 1000 h, the interfacial resistance of LSF20-coated alloy is lowered by more than 23 times to that of LSM20-coated layer.