Electrochemical and Catalytic Behaviors of Ni–YSZ Anode for the Direct Utilization of Ammonia Fuel in Solid Oxide Fuel Cells

In this study the electrochemical performances of Ni–YSZ anode in humidified H2, NH3 and CH4 fuels were compared under almost the same partial pressure of oxygen at 500–800°C. The cell performance was significantly affected by fuel species and operating temperature. The single cell exhibited higher performance in wet NH3 as 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. Thus, it was clarified that NH3 is a preferable fuel rather than CH4 for the direct use in SOFCs. Furthermore, the kinetics study on ammonia decomposition over Ni–YSZ anode was conducted at 600°C. Although the ammonia decomposition increased with increasing ammonia concentration, the decomposition reduced in the presence of hydrogen in the reactant gas. Such a behavior was not confirmed at 850°C. These results indicated the inhibition effect of hydrogen for ammonia decomposition, which will be the key factor for the design of anode and the operating condition setting.