A review on recent status and challenges of yttria stabilized zirconia modification to lowering the temperature of solid oxide fuel cells operation

Solid Oxide Fuel Cells (SOFCs) are an electrochemical energy converter that receives the world's attention as a power generation system of the future owing to its flexibility to consume various types of fuels, low emission of greenhouses gases, and having high efficiency reaching over 70%. A conventional SOFCs operates at high temperature, typically ranges between 800 to 1000 degrees C. SOFCs use yttria-stabilized zirconia (YSZ) as the electrolyte, which exhibits excellent oxide ion conductivity in this temperature range. However, this temperature range poses an issue to SOFCs durability, as it leads to the degradation of the cell components. In addition, SOFCs application is limited and difficult to implement for the transportation sector and portable appliance. A viable solution is to lower the SOFCs operating temperature to intermediate (600 to 800 degrees C) or low (<600 degrees C) operating temperature. The benefit of this way, cell durability will improve, as well as other advantages such as facilitates handling, assembling, dismantling, cost reduction, and expanded the SOFCs application. Nonetheless, the key challenge for the issue is finding suitable electrolyte, as YSZ have lower ionic conductivity at low and intermediate temperature range. The aim of this paper is to review the status and challenges in the attempts made to modify YSZ electrolyte within the past decade. The resulting ionic conductivity, microstructure, and densification, mechanical and thermal properties of these 'new' electrolytes critically reviewed. The targeted conductivity of modification of YSZ electrolyte must be exceeded >0.1 S cm(-1) to enable high performance of SOFCs power generation systems to be realized for transportation and portable applications. Based on our knowledge, this paper is the first review which focused on the recent status and challenges of YSZ electrolyte towards lowering the operating temperature.