Development Of The Electrolyte For Sulfur-Oxygen SOFC And Design And Manufacturing Of The Cells

Sulfur-oxygen SOFC, a new type of solid-state energy conversion devices which using S-vapor or SO2 as fuel gas instead of hydrogen. Currently, the main structure of SOFC cell stack was divided into two types, include plate type and tube type. In comparison, the plate type SOFC becomes the hotspot in currently years because it has good performance in electrochemistry, easy for manufacturing and low-cost. As important parts of SOFC, how to use a simple and low-cost way to preparing a high performances electrolyte has caused more and more attention of the researchers. In this paper, the electrochemistry performances of Sulfur-oxygen SOFC electrolyte under different conditions were studied, and the preparation of single cells and design manufacturing of the stack cells for Sulfur-Oxygen was also studied.(1) The powders of La0.8Pr0.2CrO3 and LSM were prepared by sol-gel method, which has been used as Sulfur-Oxygen SOFC anode and cathode materials, Furthermore, all of them were investigated by XRD and SEM.(2) Using PES as electrolyte dissolvent for Sulfur-oxygen SOFC, and arranged a series of conditions to development of the electrolyte for Sulfur-Oxygen SOFC by using the orthogonal experiment method, both sides of the electrolyte piece were coated with cathode and anode materials by the methods of coating, the structure of “cathode/wiremesh‖electrolyte‖wire-mesh/anode” have made after dry and sintering, and with bases of it we have made a single cell electrochemical systems. The electrolyte which prepares by the different methods was tested when S-vapor was used as fuel gas, the result showed that the best preparing condition of sulfur-oxygen SOFC electrolyte: the mass ratio between electrolyte powders and PES was 5:1(g/mL), Na2SO4(25wt%)-YSZ as composite electrolyte, 5YSZ as electrolyte powers, the presintering temperature of electrolyte select 400 ℃. The single cell which using the best preparing condition of sulfur-oxygen SOFC electrolyte was tested, the result showed that in 780 ℃ it has the maximum open-circuit voltage of 814 mV, and the cell obtain maximum power density of 37.7 mW/cm2 when the cell current density is 93 mA/cm2.(3) 304 stainless steel has been chosen as the cell framework, with the composited single cells inserted into the interval groove one by one and the structure sealed, theⅠ-type cell stack was finished. The stack was tested with S-Vapor as fuel gas, the result showed that the maximum open-circuit voltage is 697 mV at 760 ℃, after 20 hours uninterrupted work,the open circuit voltage decay rate was 5.6%, while the decay rate reached 50.7% after 10 times thermal shock cycling, the stack obtain the maximum power density of 33.3 mW/cm2 when the output current density is 104 mA/cm2.(4) The Ⅱ-type stack is finished with the “stainless steel frame-electrolyte” integration structure, which consist of cell gaskets, bolts to compact and sealant to seal. The stack is also tested with S-Vapor as fuel gas, the result showed that the maximum open-circuit voltage is 753 mV at 770 ℃, after 20 hours uninterrupted work, the open circuit voltage decay rate was 10.4%, while the decay rate reached 59.4% after 10 times thermal shock cycling, the stack obtain the maximum power density of 39.4 mW/cm2 when the output current density is 109 mA/cm2, a little higher thanⅠ-type stack. by comparison the performance of those two type of stack, Ⅱ-type stack appears to be a better performance than Ⅰ-type stack.