Physico-electrochemical properties and long-term stability of Mn1.45-0.5xCo1.45-0.5xCuxY0.1O4 spinel protective coatings on commercial metallic interconnects for solid oxide fuel cells

Abstract

The application of ceramic coatings has been presented as an effective method to suppress the oxidation scale growth and Cr evaporation of ferritic stainless steels used in solid oxide fuel cell (SOFC) interconnects. In this work, Mn1.45-0.5xCo1.45-0.5xCuxY0.1O4 materials with various Cu contents (x=0.1, 0.3, and 0.5) were synthesized through a facile glycine nitrate process as a protective coating on a metallic interconnect (SUS 441). It was observed that the lattice parameter decreased from 8.31Å (x=0.1) to 8.22Å (x=0.5) with increasing Cu content (x). The effects of Cu content (x) on the phase stability as well as sintering, electrical, and thermal expansion were investigated. The results confirmed that the Mn1.3Co1.3Cu0.3Y0.1O4 spinel had the highest electrical conductivity of 115 Scm−1 at 800°C and an average thermal expansion value of 11.98×10−6K−1 in the temperature range of 20–1000°C. The ASR of Mn1.3Co1.3Cu0.3Y0.1O4 coated SUS441 (7.7×10−5Ω-cm2 at 800°C) was 3 orders of magnitude lower than that of the uncoated sample. Moreover, the Mn1.3Co1.3Cu0.3Y0.1O4 coated interconnect exhibited excellent long-term stability up to 1000h at 800°C without any observable degradation, while the ASR of the uncoated sample increased by >850% for 1000h (from 0.001Ω-cm2 to 0.06Ω-cm2) under the same conditions. The oxidation kinetics obeying the parabolic law with a rate constant of Mn1.3Co1.3Cu0.3Y0.1O4 (1.64×10−9mg2cm−4s−1) was 4 orders of magnitude lower than that of bare SUS 411 (7.4×10−5mg2cm−4s−1) at 750°C for 2000h. These results demonstrate that the Mn1.3Co1.3Cu0.3Y0.1O4 is a promising coating material with high electrical conductivity and excellent durability for metallic interconnects of intermediate-temperature SOFCs.