Ceramic membranes for intermediate temperature solid oxide fuel cells (SOFCs): state of the art and perspectives

Solid oxide fuel cells (SOFCs) have suitable perspectives for application in the field of distributed generation of electrical energy especially for small and medium power sources (50 kW(el)). The main advantages of SOFCs rely on the high conversion efficiency and low environmental impact. In this field the research goal of the next years is to lower the operating temperature of these devices from 800-1000 degrees C to 500-700 degrees C. The intermediate temperatures (500-750 degrees C) SOFCs (IT-SOFCs) are expected to introduce several advantages including: rapid start-up and shut-down, lower fabrication costs due to a wider range of suitable materials (especially for interconnects), a large range of applications, improved durability and lifetime. However, lowering of the working temperature will affect the electrochemical processes occurring at the electrode/electrolyte interface. As a result, these processes may become the limiting factors for the cell performance. However, the development of novel IT-SOFCs will depend on new materials combination: (i) ceramic electrolytes assuring fast ionic transport at lower temperatures, (ii) electrodes with good electrocatalytic activity for the reduction of oxygen (cathode) and for the fuel oxidation (anode) in the required temperature range. This chapter deals with a survey of the current research on advanced materials to be used as electrolyte for intermediate or low temperature SOFCs. Specific properties such as reaction mechanism, chemical compatibility, effects of dopants and ionic conductivity are discussed.