SOFC system and technology

Compact size solid oxide fuel cells (SOFCs), which will be operated at reduced temperature, are becoming a frontier of R and D. These compact size SOFCs will fit well with intermittent loads, of which share in energy system is increasing today, whereas the “conventional SOFCs” will be effectively operated with stationary mode. For such compact size SOFCs, throttle down operation following intermittent loads will be profitable because low current density gives higher efficiency. SOFCs are not suitable for quick start up. It was estimated that the hot standby mode would be more acceptable than cold start mode from the viewpoint of heat loss. The merit of internal reforming will also be lost for the reduced operation temperature. In order to overcome this problem, an electrochemical oxidation of deposited carbon was tested and a new direct internal reforming concept using this carbon deposition was proposed. In order to develop cheap compact size, reduced temperature SOFCs, the feasibility of anode supported SOFCs was investigated on Zr(Sc)O2, Zr(Y)O2, Ce(rare earth)O2, (La,Sr)(Ga,Mg)O2 electrolytes, examining applicability of wet co-fire process and electrode activity. The feasibility was confirmed with zirconia, not yet with ceria due to its fragility, and pessimistic with (La,Sr)(Ga,Mg)O2 due to Ni diffusion during co-firing.