| dc.description.abstract | In this study, ammonia is doped into a pressurized syngas-fueled (35% H2 + 65% CO) solid oxide fuel cell (SOFC). The objective is to explore whether can ammonia inhibit the carbon deposition of syngas SOFC? The carbon deposition can be formed when the carbon monoxide in the syngas undergoing the Boudouard reaction that is an exothermic reaction which is prone to occur at low temperature (500~700oC) condition of SOFC. Our previous study showed that the syngas-fueled SOFC can operated stably 25 hour at the operating temperature (T) of 750oC and operating pressure (p) of 1atm, without any carbon deposition. However, at T = 750oC, syngas-fueled SOFC can only operate 10 hour when p increases to 3 atm, then the occurrence of severe carbon deposition results in deterioration of cell performances. When p = 1 atm, syngas-fueled SOFC can only operate 7 hour when T decreased to 700oC, then severe carbon deposition was occurred. In this study, ammonia was doped to the anode syngas fuel, proved that the ammonia can preferentially occupy the acid sites of Ni-anode catalyst resulting in the decreased of the coke formation. Experiments were conducted in an already established high- temperature and high-pressure dual-chamber SOFC facility together with cell performance measuring equipment (including electrochemical impedance spectroscopy). We measured the cell performance, impedance spectra, and durability of the syngas-doped-ammonia-fueled button anode-supported cell (ASC; 530 μm Ni-YSZ/3 μm YSZ/15μm LSC-GDC) under different T and p conditions. Results show that at T = 700oC and p = 1 atm, the syngas-doped-ammonia-fueled ASC can operate stably for 28 hours, without any carbon deposition, also the operating time was longer than the previous study. It was found that the ASC can operate up to 40 hours at T = 650oC and p = 1 atm, without any degradation. This is because the decomposition rate of ammonia to hydrogen and nitrogen will decrease with decreasing the operating temperature, so that there was more residual ammonia left at lower operating temperature (650oC), which was sufficient to occupy the acid sites of Ni-anode catalyst for being able to inhibit the carbon deposition. At T = 650oC, the cell performance of syngas-doped-ammonia-fueled ASC was increased with elevating the operating pressure (p = 3 atm). However, the ASC became vulnerable to carbon deposition after 32 hours operation, resulting in the degradation of cell performance. Scanning electron microscope (SEM) and energy dispersive X-Ray (EDX) analysis showed the carbon atomic ratio (At. %) of the cells’ anode surface after treated at T = 650oC and p = 1 atm, T = 700oC and p = 1 atm, and T = 650oC and p = 3 atm were 16.08 %, 87.23 %, and 68.53 % respectively. In the end, this thesis obtains two conclusions: (1) the doping of ammonia to syngas fuel promotes the reduction of carbon deposition, especially at atmospheric pressure and at T = 650oC conditions, the effect of doped ammonia to the inhibition of carbon deposition was more significant. (2) The higher operating pressure condition was not conducive to the suppression of carbon deposition by doped ammonia, even at T = 650oC, showed that syngas-fueled SOFC which using nickel base as anode catalyst was difficult to work for a long period under high pressure conditions. | en_US |