The effects of thermal aging on metallic interconnects of solid oxide fuel cells

Abstract

For solid oxide fuel cells (SOFCs), metallic interconnects (ICs) are crucial components to add to the electrochemical catalyst electrodes. The high temperature operation condition in SOFCs is an extremely degrading factor for metallic ICs. Three metallic ICs have been selected in this thermal aging study. IC-1 and IC-2 contain similar Mn/Cr compositions. The thermal mechanical property of IC-2 is better than that of IC-1, attributed to the inclusion of rare earth elements. IC-3 has lower chromia composition, whereas IC-1 and IC-2 have higher Cr contents. Thermal aging is introduced under ambient atmosphere at 800°C from 0 to 100 h. X-ray diffraction study of the IC oxide scales shows growth of (MnCr)3O4 with the spinel structures. Scanning electron microscopy and energy dispersive spectroscopy (SEM/EDS) reveal the thickness and spinel particles for the three ICs, the oxide layers at about 0·9–1·3 μm thick and the spinel sizes at 1·0–1·3 μm. The oxide weight gain studies have shown that IC-3 is the more readily oxidised IC, with an estimated oxidation rate of ∼1·98×10−7 g2 cm−4 s−1 at 800°C. Thus, IC-3 should be better coated with a protective layer for SOFC applications. For the thermal Cr diffusion study, we applied homemade glass sealant on the surface of IC-1. After thermal aging for 1000 h under ambient atmosphere at 800°C, we examined the sample with micro-Raman. The cross-sectional microstructures were studied with SEM/EDS. Both Raman and SEM/EDS results indicated that the Cr ions penetrated into the glass sealant by ∼65 μm. The oxide scales on ICs are influential on the electrical conductivity. The electrochemical impedance spectroscopy study on IC-2 samples after thermal aging is also shown.