A study of materials for fabrication of intermediate temperature solid oxide fuel cells electrolyte using microwave energy

Abstract

Fuel cells are emerging as an alternative for the direct conversion of fossil fuel to electrical energy. Solid Oxide Fuel Cells (SOFCs) are particularly attractive because they have the highest efficiency of any conventional fuel cell design and the potential to use many fuels including gasoline and diesel without expensive external reformers that create more volatile chemicals. Solid oxide fuel cells (SOFC) are very attractive due to their high efficiency and very low pollutant emission. Until now, solid oxide fuel cell systems have been based mainly on Yttria-stabilized zirconia (YSZ) ceramics because of their nearly pure oxygen conductivity in oxidizing and reducing atmospheres as well as good mechanical properties. ZrO2-based electrolytes however require high operating temperature of 1000°C in order to maintain high oxygen ionic conductivity. Major promising advancements have been achieved in recent years in the area of high temperature fuel cells (SOFCs). These high operating temperatures demand large fabrication costs and accelerate the degradation of the fuel cell systems, expensive materials for fuel cell interconnector, long start-up time and large energy input to heat the cell up to the operating temperature. Therefore, if fuel cells could be designed to give a reasonable power output at intermediate temperatures (IT, 400-700°C), tremendous benefits may result. In particular, in the IT range ferrite steel interconnects can be used instead of expensive and brittle ceramic materials. In addition, sealing becomes easier and more reliable; rapid start-up is possible; thermal stresses (caused by thermal expansion mismatches) are reduced; electrode sintering becomes negligible. Combined together, all these improvements result in reduced initial and operating costs. Therefore, the major trend in the present research activities on SOFCs is the reduction of the operating temperature. The problem is that lowering the operating temperatures lowers the electrolyte conductivity.