Synthesis and Characterization of Ceria based Electrolyte for Intermediate Temperature Solid Oxide Fuel Cell

Abstract

Solid oxide fuel cells (SOFC) are environment-friendly energy conversion devices in which chemical energy transforms directly into electrical energy. These devices are highly efficient and can work with various fuels. In this process, apart from electricity, SOFC produces water steam as a by-product that can be used to co-generate electricity. Further, they can also be used in electrolysis mode to generate hydrogen and oxygen gases. Even though SOFCs have many advantages, the high operating temperature (i.e., 800-1000 °C) is a crucial bottleneck in realizing its full potential. High operating temperature poses several problems regarding the choice of materials, particularly for interconnects and glass seals. It also leads to faster interfacial reactions, material degradation, and increased operational and fabrication costs. These complexities can be overcome by reducing the operating temperature to less than 800 °C. Electrolytes are vital components in deciding the operating temperature of SOFC. The conventional SOFC uses yttria-stabilized zirconia (YSZ) as an electrolyte, which operates between 800-1000 °C. High ionic conductivity, chemical and thermal stability, as well as a dense structure, are some of the essential requirements for an electrolyte. Doped ceria is a better choice for electrolytes at intermediate temperature (500-800 °C) due to its high conductivity and better compatibility with other cell components in this temperature range. The present thesis investigates Gd and Sr doped and co-doped ceria samples with a focus on solid oxide fuel cell development. The samples are synthesized using an ultrasound-assisted sol-gel auto-combustion method. The samples were characterized for their structural, thermal, and electrical properties. The selected electrolytes are sandwiched between the anode and cathode and tested in real SOFC conditions. The thesis is divided into six chapters, with a list of references provided at the end of the thesis. Chapter 1 introduces fuel cells and SOFCs with a brief account