State-of-the-art solid oxide fuel cells (SOFC) are among the main candidates for clean energy technology due to their high efficiency, fuel flexibility, low air pollution, and minimal greenhouse gas emission. However, high operational temperature of SOFC is a greater challenge in commercialization of these devices for low cost and portable applications. High temperature operation of SOFC degrades its performance with aging, limits the selection of materials for fuel cell components, and increases the fabrication cost. Thus, there have been enormous efforts to improve the properties of existing materials and develop new materials for SOFC components in order to lower the operating temperature of SOFC. Recent advances in thin film technology have also been utilized to develop new materials with improved properties for SOFC. One of the key components in SOFC is the electrolyte and several research groups are working on developing new electrolyte materials. In this chapter, we will discuss the recent advances in thin film SOFC electrolytes. This extensive discussion includes the evolution of doped ceria, doped zirconia, and multilayer hetero-structured thin film electrolytes. The newly developed nanoscale thin films and multilayer hetero-structures with improved oxygen ionic conductivity will have significant impact on SOFC devices.
Introduction
Background of Solid Oxide Fuel Cells (SOFC)The latest U.S. energy reviews revealed that more than 80 % of the energy consumed in the world is still produced by non-renewable energy sources such as petroleum, natural gas, and coal [1]. Moreover, it is projected that world energy consumption will grow by 56 % from 2010 to 2040. Therefore, from a long-term energy perspective, clean energy technologies are needed to utilize primary energy