Long-term stability of segmented type cell-stacks developed for residential use less than 1 kW

Segmented-in-series type cells-stack under development has many advantages such as reduced temperature operation, high-voltage/ low-current power generation, and lower in material cost of electrical insulating substrate compared to Ni based substrates for anode-supported cells. Another key advantage is that there is no need for alloy interconnects. This would make the cell-stack more durable than other types of cell-stacks having alloy interconnects. In this study, the durability of the segmented cell-stacks was investigated. Durability tests in an electric furnace were conducted under a standard condition as well as under controlled severe conditions in which a particular test parameter was set to severe value in order to define accelerating factors of deterioration. In the real system environment, the degree of variation of the parameters is larger than that in the standard condition in electric furnace. Therefore in order to estimate the degradation phenomenon in the real system, the durability tests were conducted also in the simulated system condition in the furnace with temperature distribution of 120°C and reformed methane as a fuel. Cell-tacks under the "standard" condition at a current density of 0.24 A/cm² and temperature of 775°C with small temperature distribution less than 30°C showed stable performance for experimental period up to 4000 hrs. The degradation rates of the cell-stacks were found to be 0.27-1.04%/1000-h with an average degradation rate of 0.6%/1000-h. Two accelerating factor of deterioration have been found through durability tests under controlled severe conditions. Then the cell-stacks were modified successfully to improve the durability with lower degradation rates.