Design, production and characterization of glass-ceramic based sealants for solid oxide fuel cells applications

Abstract

Planar solid oxide fuel cells (SOFCs) are capable of achieving higher power density than tubular SOFC, but hermetic seals are required to prevent mixing of the fuel and oxidant, It is still a challenge to develop sealing materials that retain desirable physical properties, are chemically compatible with other fuel cell components at high temperature (e.g. 800 °C) in a wide range of oxygen partial pressure, and remain operational over thousands of hours. In most planar SOFCs stacks designs, the interconnect is sealed to the cell components. The seal between the metal interconnect and the ceramic SOFCs components presents a challenge. Design, development and implementation of reliable sealants may contribute to the destiny of SOFC electrical power-generation technology. Glass-ceramics, which can be prepared by controlled sintering and crystallization of glasses, possess superior mechanical properties and higher viscosity at the SOFC operating temperature than glasses. The application of a protective coating on the alloy surface has been proven as a practical and effective method to reduce corrosion rates and/or inhibit Cr volatilization and thus cathode poisoning. Though some coatings can be highly effective in reducing corrosion rates and reducing area specific resistance of metallic interconnects, their properties for blocking chromium diffusion are limited and need more research on advanced materials and new processing methods. Furthermore, in the complex contest of the SOFC stack, the interconnect/sealant interface plays a key role in the stack reliability, efficiency and durability that depends also on the gas tightness provided by seals during SOFC operation for thousands of hours. It is desirable that reactions between the sealant and the coating or the metallic interconnect are limited during SOFC relevant operating conditions, otherwise spallation and detachments at the interfaces can occur and determine leakage and SOFC degradation. Finally, different approaches are used in this work for the integration (i. e. joining) of ceramic and metallic components in solid oxide fuel cells (SOFCs) stacks, where dissimilar materials have to be joined and sealed for a reliable long-term operation. In particular, the thermo-mechanical compatibility of sealants with other stack components critically influence the reliability and the robustness of SOFCs devices.