Abstract
Metallic interconnects represent the main component of a solid oxide fuel cell (SOFC) stack in terms of weight and volume. They are typically made of ferritic stainless steel (FSS) coated on the air side. At the stack operating conditions, the interconnect is exposed to a dual atmosphere: air at the cathode side; fuel (a hydrogen-rich mixture) at the anode side. The stacks considered in this study were field operated in reformed natural gas for 5000, 9000 and 20,000 h respectively. The analyzed interconnects are made from CROFER22APU and coated on the air side with Co-Mn base spinel. One interconnect has been studied for each stack by sampling and preparing cross section the inlet and outlet positions. The samples were characterized by SEM-EDXS in order to investigate the evolution of the interconnect at the air side. The interaction between the metal substrate and the coating is investigated highlighting the formation of chromia based thermal grown oxide (at the FSS/coating interface) and the solid-state diffusion of Cr and Fe from the metal into the coating. The microstructural features evolving as a function of time are also quantified.
Highlights
In the last few decades, studies have focused on the priority of producing technologically efficient power sources by limiting environmental damages
Two areas will be described in the sections, called ribs and channels according to the Figure 2 displays the macroscopic evolution of the metallic interconnects (MICs) operated up to 20,000 h at the air side
This investigation allows the estimation of the coatings effectiveness to mitigate the oxide growth on the metal surface, the consequent chromium solid state diffusion towards the cathode and the time dependence under operating conditions of the structural and chemical features of the layers
Summary
In the last few decades, studies have focused on the priority of producing technologically efficient power sources by limiting environmental damages From this perspective, solid oxide fuel cells (SOFCs) have reached a certain technology readiness level for a clean method of electric energy production using hydrogen (or hydrogen rich gases) as fuel. The physical and chemical properties of the MIC are modulated in order to obtain good and reliable performances of the entire SOFC at high temperatures [8] These components are typically made of ferritic stainless steels (FSSs) that have a suitable oxidation resistance, a coefficient of thermal expansion (CTE) matching with the one of the other components of the fuel cells (11.5–14.0 × 10−6 K−1 from room temperature to 800 ◦ C), good thermal and electrical conductivity, good manufacturability, suitable mechanical properties, easy fabricability, and affordable costs [6,7,9,10,11]. Their high Cr content promotes the Energies 2020, 13, 6487; doi:10.3390/en13246487 www.mdpi.com/journal/energies
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