From rare earth doped zirconia to 1 kW solid oxide fuel cell system

Abstract Toho Gas R&D efforts and achievements regarding solid oxide fuel cells (SOFCs) from rare earth doped zirconia to 1 kW SOFC system are described in this article. In this research, the use of Sc 2 O 3 –ZrO 2 (scandia stabilized zirconia, ScSZ), which has the highest oxide ion conductivity among the zirconia systems, was investigated as an electrolyte for SOFCs. To improve the performance and mechanical reliability of SOFC cells and stacks, tetragonal phase ScSZ ceramic sheets were developed as electrolytes for SOFCs. They have flexibility, high-strength and twice the conductivity of a Y 2 O 3 –ZrO 2 (Yttria stabilized zirconia, YSZ) system. Because of this electrolyte, the SOFC operating temperature was reduced to 1073 K. Also, to validate the performance of this cell, the first Japanese-made 1 kW SOFC system was fabricated, and its carefully designed internal manifold type 68-cell stack produced an output of over 1 kW (DC) at 1073 K under thermal self-sustaining conditions.