Assessment of Mechanical Reliability of Planar SOFCs in view of Selection of Materials and Operating Conditions

摘要

Since the successful operation of a 1.7 kW planar SOFC module with direct internal reforming (DIR) of methane in 1998, we have focused on the establishment of mechanical reliability of planar SOFCs. In operation of planar SOFCs, cells are subject to stresses resulting from mismatch of thermal expansion coefficient (TEC) of cell components and temperature distribution in cells, which may cause cracking of the cells. To increase the mechanical reliability, the stresses should be relieved by selecting appropriate cell materials and operating conditions. This study is aimed at identifying appropriate materials and operating conditions through experimental and numerical evaluations. As for selecting the cell materials, several combinations of separators and electrolytes with different TEC were bonded, thermal-cycled between r.t. and 1000°C in an in-situ detection system for mechanical failures of the electrolyte, which has clarified the allowable difference in TEC. As for selecting the operating conditions, cell-stacks are heated to 1000°C and the internal heat evolution is increased by increasing the current until the electrolyte sheet is cracked, which clarifies the allowable temperature distribution in the cells.