Composite Electrolytes and electrodes for Intermediate Temperature Hybrid Fuel Cells

Moving away from conventional solid oxide electrolytes, hybrid fuel cells based on composite electrolytes (a solid oxide electrolyte and a molten alkaline carbonate phase) exhibit promising performance due to the high electrolyte conductivity within the so-called intermediate temperature ranges (400-600 C). These electrolytes are a blend of those traditionally used in Solid Oxide and Molten Carbonate Fuel Cell technologies, where the ceramic phase might be understood as a matrix with distinct functionality with respect to the classical MCFC matrix, LiAlO2. Indeed, rare earth (either Gd or Sm) doped cerium oxide is the most general solid oxide phase used for making composite electrolytes for hybrid fuel cells. The incorporation of inorganic salts into solid oxide phase gives multi ionic conductivity (CO3, O, H) with overall conductivity of around 0.1 Scm at 600 C, which is superior to the single ionic conductivity in Solid Oxide Fuel Cells. Hydrogenated species formed from interaction with the gas phase and located in the oxide/salt interface are believed to play a major role. This chapter mainly deals with different materials used for the state of the art composite electrolytes and also explain the electrodes used for such composite electrolytes. The different processing route and its influance on the final behaviour of the composite electrolytes also will discussed. In addition, the compositional effect on the conducting mechanism will be addressed briefly.