The electrical property of MnCo2O4 and its application for SUS 430 metallic interconnect

Abstract

The conductivity of MnCo 2 O 4 spinel, the best route to form the MnCo 2 O 4 protective coating applied by the sol-gel process, and its effect on the intermediate temperature oxidation behavior of SUS 430 alloy, a typical material for the interconnect of solid oxide fuel cell (SOFC), was investigated. The phase structure and surface morphology of the coating and surface oxides were characterized by XRD, SEM and EDS; the "4-probe" method was employed to determine the conductivity of MnCo 2 O 4 spinel and the area specific resistance (ASR) of the surface oxides. The conductivity of MnCo 2 O 4 spinel is excellent, which is 2 orders of magnitude better than that of MnCr 2 O 4 spinel. Long-term thermally cyclic oxidation at 750°C in SOFC cathode atmosphere and ASR measurement have shown that calcined in reducing atmosphere followed by pre-oxidation in the air is the best technique for forming the MnCo 2 O 4 protective coating, which enhances the oxidation resistance, and improves the electrical conductivity and adherence of coated SUS 430 alloy significantly. As a result, the MnCo 2 O 4 spinel is the most potential candidate for SOFC metallic interconnect protective coating application. solid oxide fuel cell, MnCo 2 O 4 , oxidation kinetics, area specific resistance Citation: Hua B, Kong Y H, Lu F S, et al. The electrical property of MnCo 2 O 4 and its application for SUS 430 metallic interconnect.The interconnect is a critical component of the planar solid oxide fuel cell (SOFC) stack that provides electrical connections between adjacent cells, physically separates the oxidant and fuel gases, and distributes the gases to electrodes. Because of the relatively high operation temperature (1000°C), the requirements for interconnect materials are quite stringent. The conventional ceramic interconnect material mainly is LaCrO 3 perovskite with Sr or Ca doping, which is difficult to fabrication and has a high cost. With the recent progress in materials, fabrication and design of SOFC, the SOFC operation temperature reduces from near 1000°C to an intermediate temperature range of about 600−800°C. It allows the use of metallic alloys as interconnect materials with advantages in electric and thermal conductivities, mechanical *Corresponding author (email: plumarrow@126.com) integrity, fabrication and cost [1]. Among all metallic materials, Cr 2 O 3 -forming ferritic stainless steels are one type of the most promising interconnect material candidates and have been intensively investigated due to their attractive coefficient of thermal expansion (CTE) compatibility and excellent oxidation resistance [2−8]. However, the oxidation of Fe-Cr alloys (such as SUS 430, Crofer 22 APU, ZMG 232, E-Brite) is inevitable during SOFC operation. The thermally grown oxide scales (mainly consisted of Cr 2 O 3 and Mn-Cr spinel) of the ferritic stainless steels may overgrow to as thick as tens of micrometers during SOFC's lifetime, resulting in high electrical resistance and even scale spallation, and subsequently degraded the stack performance dr...

Mechanochemical Processing of Mn and Co Oxides: An Alternative Way to Synthesize Mixed Spinels for Protective Coating

“…The value estimated above 700°C is comparable to that obtained for the Co:Mn = 2:1 sample and to literature data, ranging between 0.2-0.4 eV. 6,22 Small differences found in this study can be due to the incomplete effectiveness of the sintering process on the treated powders, characterized by highly defective and nanostructured particles. Further studies will be carried out to deeply investigate conduction phenomena in such samples.…”

“…The high activation energy value calculated for 500°C–700°C temperature range must be related to the low‐temperature dual‐phase nature of the compound. The value estimated above 700°C is comparable to that obtained for the Co:Mn = 2:1 sample and to literature data, ranging between 0.2–0.4 eV . Small differences found in this study can be due to the incomplete effectiveness of the sintering process on the treated powders, characterized by highly defective and nanostructured particles.…”

Low temperature processed MnCo2O4 and MnCo1.8Fe0.2O4 as effective protective coatings for solid oxide fuel cell interconnects at 750 °C

“…It was similar (0.67 eV) to uncoated samples suggesting the same mechanism of electrical conduction or rather that part of the oxide scale/coating that dominate the resistance is the same. In some other studies, the activation energy of Mn,Co spinels has been measured to be ~0.2 eV, whereas activation energies for Cr2O3 and Mn,Cr spinels have been reported to be 0.51 eV and 0.44 eV respectively [63]. The ASR measured here is the sum of the thermally grown chromia scale, the reaction layer (spinel structure) and the coating.…”

Effect of Sr and Ca dopants on oxidation and electrical properties of lanthanum chromite-coated AISI 430 stainless steel for solid oxide fuel cell interconnect application

“…All coated samples presented a near parabolic behavior. Considering the long term exposure, and assuming the oxidation process as diffusion controlled, according to the parabolic law, the oxide scale weight change was proportional to the square root of time [11,19,41]:…”