Sulfur Poisoning of LSCF Cathode in Single Step Co-fired SOFC

Murata Manufacturing Co., Ltd. has been developing planar-type solid oxide fuel cells (SOFCs) based on new design concept.  The cell is fabricated by a single-step co-firing process and consists of an electrolyte, electrodes, current collectors, gas-separators with manifolds, and gas-flow channels. The membrane electrode assembly (MEA) is sandwiched between ceramic gas-separators with via-hole electrodes providing electrical paths between cells. Removing metal interconnects around cathode in the cell enables reducing Cr vapor from metal and achieving high durability. A long-term operation has been carried out at 750°C over 8000h under galvanostatic condition. Single cell voltage degradation rate was less than 0.20%/kh after 2000h operation, and Cr poisoning in the LSCF cathode after long term operation over 8000h was not observed. From these results, the cell structure is effective to reduce Cr vapor in the cathode. But Sulfur distribution in the cathode was observed by analyzing in detail. Larger amount of Sulfur to form SrSO₄ was distributed at the air channel on the upstream than that on the downstream. And furthermore, Co segregation was observed in LSCF near the GDC barrier layer at the air channel on the upstream. To study sulfur poisoning mechanism, SO₂ poisoning test was carried out with various temperature and current density. Distribution of Sulfur and Co depended on operating temperature and current density.