Performance evaluation of a new Fe-Cr-Mn alloy in the reducing atmosphere of solid oxide fuel cells

Abstract

A newly designed Fe-Cr-Mn alloy, considered as a candidate intermediate-temperature solid oxide fuel cell (SOFC) interconnect material, was cyclically oxidized at 650 °C, 750 °C, and 850 °C in a reducing atmosphere consisting of N2+3.75 vol% H2+25 vol% H2O(g) and corresponding to the SOFC anode environment. Results indicate that this alloy possesses good oxidation resistance and acceptable electrical conductivity at 750 °C in the reducing atmosphere. During the 1000 h oxidation, the oxide scale formed on the substrate at this temperature consists of an inner layer of Cr2O3 doped with Ti, a Mn-rich middle layer of Mn-Cr spinel and Mn2TiO4, and a top layer of MnO, with an overall thickness of around 3 μm. The oxidation kinetics at 750 °C obey a parabolic law with rate constants of 1.37 × 10−13 g2 cm4 s−1 from 0 to 130 h, and of 8.84 × 10−14 g2 cm−4 s−1 from 130 to 1000 h. The area specific resistance (ASR) of the oxide scale measured at 750 °C is 16.3 mΩcm2, which is higher than that formed in the oxidizing atmosphere but is still within the maximum limit of 100 mΩcm2, required for metallic interconnects. The increase in oxidizing temperature from 650 °C to 850 °C promoted the outward diffusion of Mn and Ti ions, thus changing the composition and morphology of the formed oxides; in addition, the oxidation rate of the alloy increased dramatically, leading to an increase of both the oxide scale thickness and the ASR values.