| Summary: | 碩士 === 國立中央大學 === 機械工程學系 === 106 === This thesis applies an already-established high-pressure and high temperature SOFC testing platform using a button cell (smaller reactive area; 1.54cm2) and a planar cell (large reactive area; 16cm2) to measure the cell performance and electrochemical impedance spectroscopy of anode-supported cell (ASC) fueled with ammonia. We investigate the impact of the temperature (T), the flow rate and the pressure (p) on the cell performance of different cells with different reactive area. Then we compare the results of both ammonia and hydrogen SOFCs. This study includes four parts. First, we compare the cell performance and electrochemical impedance spectroscopy of two ASC which has different cathode materials (i.e. lanthanum strontium cobaltite, LSC; lanthanum strontium cobaltite ferrite, LSCF). The second part is to measure the pressurization effect and the stability test of ASC (Ni-YSZ/YSZ/LSC) using by ammonia as a fuel. The third part is to investigate the flow rate effect of cell performance of ASC (Ni-YSZ/YSZ/LSC) fueled by ammonia at three different temperatures (600、650、700 oC). The fourth part is to compare the pressurized effect of ASC which has different reactive area. For the first and second parts, results show that at 750~850 oC, two kinds of ASC using ammonia as a fuel have almost the same cell performance as hydrogen-fueled SOFCs. This is because at 750 oC and above ammonia decomposes into H2 and N2, then following by H2 oxidation reaction to form H2O. Regardless of fuels (ammonia or hydrogen), the cell performance increases with increasing p and T. It is found that the ohmic polarization resistance is independent of p, but it decreases with increasing T. The total polarization resistances decrease with increasing T and p. The cell with different cathode material of LSC has higher electronic conductivity than LSCF, so it has better cell performance. The stability test of ASC is conducted at 750 oC under both 1 atm and 3 atm and at 0.8 V. After 90 minutes stability test, the cell of ASC fueled with ammonia has no degradation, even with a slight increase of power density (1-3%).
The third part shows that increasing the flow rate of ammonia cannot increase the cell performance when the temperature at 600 oC and below. Because increasing the flow rate can decrease the fuel residence time and the ammonia decomposition decreases with decreasing the residence time, resulting in the lower hydrogen concentration in the vicinity of anode. Thus the increase of flow rate can result in an increase of the total polarization resistances, since the product and nitrogen can increase the gas diffusion. The fourth part is to compare the pressurized effect of ASC which has different reactive area. From the EIS data, we find that the smaller reactive area of ASC is dominated by the gas diffusion having characteristic frequencies between 10~100Hz. For the larger reactive area of ASC, the dominated polarization is via gas conversion having characteristic frequencies less than 1 Hz. Such difference is that the larger reactive area of ASC can consume the fuel faster, resulting in less fuel and more product in the outlet gas which in turn increases the gas conversion resistance. The total polarization resistances decrease with increasing p for both small and large reactive area of ASCs, indicating that pressurization increases the cell performance. These results should be useful for the future development of ammonia SOFC power generation system.
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