Conductivity and Oxidation Behavior of Fe-16Cr Alloy as Solid Oxide Fuel Cell Interconnect Under Long-Stability and Thermal Cycles

Introduction

Interconnect is one of the most important components for solid oxide fuel cell (SOFC) stacks, which should have the following properties: excellent electrical conductivity and oxidation resistance at high temperature, adequate stability in both oxidizing and reducing atmospheres, and thermal expansion coefficient (TEC) matching SOFC electrolyte, etc. [1–4]. Due to reducing operation temperature from 1000 °C to below 850 °C, metallic materials become the prime choice as interconnect for SOFC stacks [5, 6]. Fe–Cr alloys were reported to meet the performance requirement of SOFC stacks, where the value of TEC was quite close to that of other SOFC components and the processing method of this kind of alloy was comparatively simple [7–10]. The Cr element in Fe–Cr alloy is very easy to be oxidized, resulting in formation of the Cr₂O₃ oxidation film [11]. The Cr₂O₃ oxidation film can effectively prevent other metallic ions from diffusing. In addition, MnCr₂O₄ spinal phase can also form on the exterior (air/oxide interface) of Cr₂O₃ oxide layer, as long as there is a little Mn element in the Fe–Cr alloy. The oxide phases of Cr₂O₃ and MnCr₂O₄ all have a good electrical conductivity at high temperature, which makes Fe–Cr alloys both have a comparatively high-temperature oxidation resistance and electrical conductivity [12]. As the Fe–Cr alloy has a relatively strong oxidation resistance and good electrical conductivity below 850 °C, Fe–Cr alloy has been one of the most promising materials for SOFC stack interconnect, in which Fe-16Cr alloy is widely used due to its desirable performance and low cost [13, 14].

The application of stacks requires sufficient durability for both long-term stability operation and thermal cycles, indicating that it is necessary for the interconnect alloy to have a good electrical conductivity and oxidation resistance under the stack operation conditions. To date, intense researches have been focused on electrical conductivity and oxidation resistance of interconnect alloys under short-term stability operation conditions [15–18]. There is little information reported on the electrical conductivity and oxidation resistance under long-term stability operation and thermal cycle conditions, especially in real SOFC stacks. This work aimed to investigate the electrical conductivity and oxidation resistance under long-term operation and thermal cycle...