| dc.description.abstract | This thesis investigates the effect of doping hydrogen into ammonia as a fuel on the planar anode-supported solid oxide fuel cell (SOFC; 400-μm-Ni-YSZ/3-μm-YSZ/12-μm-LSC-GDC; 50 x 50 cm2) to see whether it is effective for the reduction reaction of nickel nitride. The occurrence of nickel nitride is mainly due to the two-step reaction of ammonia in SOFC. First, ammonia decomposes into hydrogen and nitrogen, and then hydrogen oxidation takes pace to generate electricity. However, the decomposition reaction of ammonia is an endothermic reaction, which reduces the temperature of the cell and ammonia can mot be decomposed completely when the operating temperature is less than T < 750oC. Then the remaining ammonia can react with the anode nickel to produce nickel nitride, resulting in degradation of the anode nickel catalyst. We perform measurements of the cell performance, electrochemical impedance spectra (EIS), and thermal cycle test (TCT) of three anode fuels: ((1) H2/N2(540/360 sccm), (2) NH3/N2(360/180 sccm), and (3) NH3/H2/N2(90/300/210 sccm)) on planar SOFC under different operating temperature (T) and pressure (p) conditions via our established dual-chamber high-temperature and high-pressure SOFC testing platform (including measurement of electrochemical impedance spectra measurements). At p = 1 atm and T = 800oC, there is almost no difference of the cell performance for these three cases. This is because ammonia is completely decomposed to H2 and N2 when T ≥ 750°C. Also, increasing p decomposed increases the open-circuit voltage and cell performance at any given T, owing to the increase of p can promote the gas diffusion in the porous electrode and the adsorption rate of reactants on the electrode catalyst surface, leading to acceleration of the electrochemical reaction rate. As to TCT, the temperature range is set at T = 600oC and T = 700oC by using 4 steps per cycle: (1) maintaining at T = 700oC; (2) cooling to T = 600oC; (3) maintaining at T = 600oC; (4) heating to T = 700oC, each step having 1 hour. As such, one TCT experiment with six cycles has a total of 24 hours; the cell performance and electrochemical impedance spectra are measured for each of six cycles. Results show that as the number of cycles increases, the cell performance slowly decreases. After 6 cycles (24 hours), the cell performance of NH3/N2 decreases by 24% at p = 1 atm, but the cell performance of NH3/H2/N2 decreases by only 10%. Moreover, when p increases to 3 atm, the decremental percentage of cell performance for the case of NH3/H2/N2 reduces to 5%. These measurements suggests that doping hydrogen into ammonia in anode can significantly reduce the nickel nitride, especially at elevated pressure condition, as to be explained by EIS date. Finally, the aforesaid results are useful for the understanding of ammonia SOFC using Ni-YSZ anode when it is operated at low temperature ranges (600 ~ 700 oC). | en_US |