Durability improvement of flatten tubular segmented-in-series type cell-stacks for SOFC m-CHP

Durability tests of flatten tubular segmented-in-series type cell-stacks (FT-SIS) have been carried out in electric furnaces since FY 2008 in the NEDO project, "Development of system and elemental technology on SOFCs". In our current design eight cells are placed on both sides of an electrically insulated support and connected in series with ceramic interconnectors. A short bundle composed of four cell-stacks fabricated in FY 2009 showed a thermal cycle degradation rate of as small as 0.01 %/cycle in 100 TCs test after 2000 hour continuous operation. Then other short bundle in FY 2009 also showed a degradation rate of 0.31 %/ 1000h during the last 1000 hour of a 4000 hour continuous test at rated current density of 0.24 A/cm². Secondary ion mass spectroscopy, scanning electron microscope analyses of the tested cell-stacks indicated that inhibition of Cr poisoning in cathodes and uniform and dense formation of cathode interlayers were important for their durability improvement. In FY 2010 fabrication process of the cathode interlayers of FT-SIS cell-stacks was modified and alloy-free connectors between the cell-stacks were employed for further reduction of Cr poisoning. Durability tests of cell-stacks thus improved were conducted, and their analysis are now underway.