الفهرس 
General introductionOnly 14 pages are availabe for public view
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Abstract
This dissertation was dedicated to highlights the superiority and possibility of using ammonia directly as a fuel for solid oxide fuel cells. Moreover, finding an active Ni‒based cermet anode for direct NH3‒fueled SOFCs also one of the goals of this work. The findings can be summarized as follows; The ammonia utilization over Ni‒based cermet anode follow two‒step process; NH3 is catalytically decomposed to H2 and N2 and then H2 produced is electrochemically oxidized over anode. The electrochemical behaviour for the cell of Ni‒YSZ | YSZ | LSM in wet hydrogen, ammonia, and methane fuels under almost the same partial pressure of oxygen at 500‒800oC was studied The single cell exhibited higher performance in wet NH3 compared with that in CH4 which was caused by the difference in the catalytic activity of anode for the hydrogen production in wet NH3 and CH4. The cermet of Ni‒GDC showed higher catalytic activity for ammonia decomposition than Ni‒YSZ. In response to this, the performance of direct NH3‒fueld SOFC was improved by using Ni‒GDC anode. In order to enhance the performance of direct NH3‒fueled SOFCs, catalytic activities of metal (Pd, Ru, Rh, Mo, Fe, and Ir) promoted Ni‒GDC for ammonia decomposition were investigated. Ammonia decomposition over Ru‒promoted Ni‒GDC catalyst was the highest among the studied metal modified Ni‒GDC. Therefore, Ru and Fe‒promoted Ni‒GDC anode was prepared by infiltration technique and the electrochemical performance was studied and compared with that of Ni‒GDC with supply of hydrogen and ammonia fuel. It found that the Ru‒promoted Ni‒GDC is an active anode for direct NH3‒fueled SOFC. On the other hand, Ni-BaCe0.75Y0.25O3–δ was investigated as an anode for direct ammonia-fueled solid oxide fuel cells employing proton conducting electrolyte BaCe0.90Y0.10O3–δ (BCY10). The catalytic activity of Ni-BCY25 for ammonia decomposition was found to be remarkably higher than Ni-YSZ and Ni-GDC. The poisoning effect of water and hydrogen on ammonia decomposition reaction over Ni-BCY25 was confirmed. Long‒term stability of direct ammonia fueled SOFCs was investigated. At low temperature region where ammonia cannot be completely decomposed, the Ni-YSZ anode is actually exposed to a gaseous mixture of N2, H2, H2O, and NH3. In this case, the surface of nickel was nitrided by the remained ammonia, leading to a volumetric change of Ni particles. This possibility brings a risk to the long‒term stability of direct ammonia SOFCs with Ni-YSZ cermet anode.