Abstract
Two commercial ferritic stainless steels (FSSs), referred to as Steel A and Steel B, designed for specific high-temperature applications, were tested in static air for 2000 h at 750 °C to evaluate their potential as base materials for interconnects (ICs) in Intermediate Temperature Solid Oxide Fuel Cell stacks (IT-SOFCs). Their oxidation behavior was studied through weight gain and Area Specific Resistance (ASR) measurements. Additionally, the oxide scales developed on their surfaces were characterized by X-ray Diffraction (XRD), Micro-Raman Spectroscopy (μ-RS), Scanning Electron Microscopy, and Energy Dispersive X-ray Fluorescence Spectroscopy (SEM-EDS). The evolution of oxide composition, structure, and electrical conductivity in response to aging was determined. Comparing the results with those on AISI 441 FSS, steels A and B showed a comparable weight gain but higher ASR values that are required by the application. According to the authors, Steel A and B compositions need an adjustment (i.e., a plain substitution of the elements which form insulant oxides or a marginal modification in their content) to form a thermally grown oxide (TGO) with the acceptable ASR level.
Highlights
Interconnects (ICs) are key elements of Intermediate Temperature-Solid Oxide FuelCells (IT-SOFCs), i.e., electrochemical devices made of an array of units which directly convert, in the temperature range from 650 ◦ C to 850 ◦ C, the chemical energy of a fuel into electrical energy [1,2,3,4,5]
To 850 ◦ C, this class of materials was selected among others to replace LaCrO3 -based interconnects since it exhibits adequate application characteristics: a thermal expansion coefficient (TEC) similar to the other ceramic parts of the fuel cell (11.5–14.0 × 10−6 /K from RT to 800 ◦ C), good thermal and electrical conductivity, good manufacturability and mechanical properties, easy fabricability, affordable cost and, in the case of chromia-former steels containing over 16 wt.% Cr, the formation of a comparatively conductive and protective Cr2 O3 scale in presence of an oxidizing atmosphere [13,14,15]
◦ C for different oxidation times (i.e., 100, 200, 750, 1000, and 2000 h) compared with the at 750 °C for different oxidation times (i.e., 100, 200, 750, 1000, and 2000 h) compared with weight gaingain datadata published in literature and concerning the ferritic stainless steels (FSSs) used for stack the weight published in literature and concerning the commonly
Summary
Interconnects (ICs) are key elements of Intermediate Temperature-Solid Oxide FuelCells (IT-SOFCs), i.e., electrochemical devices made of an array of units which directly convert, in the temperature range from 650 ◦ C to 850 ◦ C, the chemical energy of a fuel (i.e., hydrogen or other fuels) into electrical energy [1,2,3,4,5]. After the successful reduction of SOFC operation temperature in the range 650 ◦ C to 850 ◦ C, this class of materials was selected among others (e.g., chromium-based alloys and Ni-Cr based alloys) to replace LaCrO3 -based interconnects since it exhibits adequate application characteristics: a thermal expansion coefficient (TEC) similar to the other ceramic parts of the fuel cell (11.5–14.0 × 10−6 /K from RT to 800 ◦ C), good thermal and electrical conductivity, good manufacturability and mechanical properties, easy fabricability, affordable cost and, in the case of chromia-former steels containing over 16 wt.% Cr, the formation of a comparatively conductive and protective Cr2 O3 scale in presence of an oxidizing atmosphere [13,14,15].
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