Fabrication and Characterization of Metal-support for Solid Oxide Fuel Cells (MSOFCs)
Chung, Kyung Sil
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Solid oxide fuel cells (SOFCs) can generate electricity with higher efficiency and reduced carbon emissions compared with conventional power generation systems. Unlike many other fuel cells, SOFCs are beneficial in terms of utilizing not only expensive hydrogen gases but also syngas and hydrocarbons. This flexibility in fuel options is one of the advantageous aspects that SOFC has over the other fuel cells. However, current research is challenged with reducing the operating temperature and finding more cost effect of ways of fabricating SOFCs. In order to widespread commercialization the high cost and stability issues associated with high temperature operation must be overcome. To address these issues, researches have aimed at reducing the operating temperature of SOFC. One option is to use alternative ceramic materials, by replacing conventional Yttria Stabilized Zirconia (YSZ) with materials possessing higher ionic conductivities at lower temperatures (e.g. 600-800°C), such as Samarium Doped Ceria (SDC). This is a critical step since reducing the operating temperature below 700°C allows the use of metal-supported cells. Use of porous metal-support made with stainless steel can provide benefits including increased durability, reduced cost, higher oxidation resistance, and tolerance to thermal resistance. This new generation of SOFC with metal as a support structure is called metal-supported solid oxide fuel cell (MSOFC). The porous metal support must satisfy several requirements: it must be porous enough (~20-40% porosity) to provide gas diffusion pathways, able to operate at high operating temperatures (600-800°C) without oxidation, and match the coefficient of thermal expansion (CTE) with that of ceramic materials (YSZ and SDC have CTE of 10-12 ppm K-1). In this thesis, the main objectives are 1) to determine suitable fabrication methods for the porous metal support and 2) characterize the fabricated metal-support with various parameters to provide guidelines for determining compatible metal supports for MSOFC. The stainless steel 400 series satisfies the above requirement and in this thesis, SS430L (d50 = 44 µm) was chosen as support materials. The porous metal support is fabricated using various precursor formulations; such formulations comprise metal support powder (SS430L), plasticizer (DOP), pore former (PMMA), binder (PVB) and solvent (ethanol). Beside the precursor formulation, the sintering process is also critical. The sintering temperature profile was determined through thermogravimetric analysis (TGA) of individual components. The sintered porous metal support was characterized for oxidation resistance, porosity measurements, CTE measurements, electronic conductivity, and SEM imaging. Correlations between precursor formulation, sintering results, the relative densities, porosities, and CTEs were established. These measurements can provide guidelines to fabricate compatible metal support for MSOFC.