Investigation of the Glass-Ceramic Sealants in SOFC Stacks

Abstract

The stack sealing is one of the most important factors in planar solid oxide fuel cell (pSOFC) applications. Two sealing approaches were used for the short stacks working under practical conditions, which are rigid bonded sealing with SiO2-BaO-based glass sealant and compressive sealing with ZrO2-based ceramic gasket. The prepared glass was characterized by inductively coupled plasma mass spectrometry (ICP-MS), scanning electron microscopy (SEM), X-ray diffraction (XRD), and dilatometry to determine its component and structural and thermal properties. Once the stack system shut down, the bubble test was used to detect and locate the leak of the stack. Then post-test characterization was conducted to analyze the failure of the sealing. SEM-EDS and XRD were used to analyze the microstructure and the crystallization of the sealant inside and its interface with the interconnect. It was observed that the crystal was formed inside the glass sealant, which strengthened the material. Good adhesion and chromium diffusion were found between the glass sealant and the metal interconnect. Moreover, the lose the sealing glass under overheating was found close to the fuel inlet, which was suggested to lead to the failure of the stack. For the ZrO2-based ceramic sealing, the crack was observed inside the sealant and the airway was obstructed by the sealing material under the compressive force. In summary, the glass sealing was more controllable than the compressive ceramic gasket. However, the glass sealant should be protected from local overtemperature.