Metallic interconnects for solid oxide fuel cell: Performance of reactive element oxide coating during long time exposure

Abstract

One of challenges in improving the performance and cost-effectiveness of SOFCs (solid oxide fuel cells) is the development of suitable interconnects materials. Chromia-forming alloys and especially ferritic stainless steels, like Crofer22APU, are considered to be among the most promising candidate materials as interconnects in SOFC stacks. However, the performance of chromia-forming materials can be limited by the low electronic conductivity of the oxide scale (high ASR -area specific resistance -value). Such degradation are unacceptable regarding the long-term operation (>40 000 h). A previous study [1] demonstrated that in air, the addition of a nanometric reactive element oxide (La 2 O 3 ) layer applied by metal organic chemical vapor deposition (MOCVD) drastically improved both corrosion rate and electrical properties of Crofer22APU and Haynes230 alloys for 100 h at 800 8C. In this present study coating performances were checked after 10 months (7500 h) and 20 months (15 000 h) at 800 8C in air. The corrosion products were carefully analyzed by SEM, EDX, and XRD. ASR measurements are realized after long time exposure. This study demonstrates that the Crofer22APU alloy has a good oxidation resistance after 15 000 h in air but this alloy has an ASR value equal to 0.370 V cm 2 . The coatings composed of a thin reactive element oxide such as La 2 O 3 resulted in an important improvement in the high temperature oxidation resistance; the ASR values are equal to 0.154 V cm 2 . Haynes230 alloy has a better oxidation resistance but the formation of an insulating Al 2 O 3 /SiO 2 layer could be detrimental.

Highly Dense Mn-Co Spinel Coating for Protection of Metallic Interconnect of Solid Oxide Fuel Cells

“…The oxide scale of Crofer 22 APU is composed of a chromia inner layer and a (Mn,Cr) 3 O 4 spinel outer layer, which is formed by the diffusion of Mn along the grain boundaries of the chromia scale. 88 The boundary between the Mn-Co spinel protection layer and the Mn-Cr spinel intrinsic scale on Crofer 22 APU is not clearly observed, which suggests that the coating layer and the substrate are chemically and thermo-mechanically compatible, forming the strong interface. Figure 6 compares the ASR data of the bare and coated Crofer 22 APU samples measured at 800…”

Thermal expansion and electrical conductivity of Fe and Cu doped MnCo2O4 spinel

“…Several materials have been investigated as protective coatings for SOFC interconnects, including rare-earth oxides [15,16] and various lanthanum-based perovskites [17][18][19]. (Mn,Co)3O4 spinel oxides were first suggested as a coating material candidate by Larring and Norby [20], and have received increasing attention over the last decade [21][22][23][24][25][26][27][28].…”

CHAPTER 6 Development of SOFC Interconnect Stainless Steels

“…Reactive element oxides could be coated to provide the reactive element effect including the reduced oxidation rate of the alloys. Fontana et al [100] demonstrated that the addition of a nanometric reactive element oxide (La2O3, Y2O3) layer applied by Metal Organic Chemical Vapour Deposition (MOCVD) drastically improved both corrosion rate and electrical properties in air of Crofer 22 APU and Haynes 230 alloys even after 20 months exposure at 800 ºC in air. During aging in SOFC conditions, La2O3 transformed into LaCrO3.…”