Ammonia is receiving attention as a hydrogen carrier because of a number of advantages over other hydrogen carriers, such as greater hydrogen content, easy liquefaction and no carbon emission. Mass production process of ammonia has also been established and well-known as the Haber-Bosch process. Among the energy systems operated with hydrogen and hydrogen-containing fuels, solid oxide fuel cells (SOFCs) are one of the candidates that can be operated with ammonia-based fuels because they can decompose ammonia on their Ni-based anodes and produce hydrogen inside the systems; this can simplify the whole system configuration and realize cost reduction. In addition, the excess heat generation from the electrochemical reaction can be effectively utilized for the ammonia decomposition reaction.

Because the ammonia decomposition reaction is endothermic, temperature distribution on the cells is likely to be altered compared with the hydrogen-fueled SOFCs. Also, charge-transfer current distribution will be affected by the temperature distribution. To understand unique characteristics of ammonia-fueled SOFCs and to propose their appropriate operation conditions, numerical analysis is indispensable because of the difficulty in the direct measurement of physicochemical properties inside the cells. However, there are not many studies found in open literature where the characteristics of ammonia-fueled SOFCs are analyzed in detail by numerical analysis.

In this study, a numerical model of ammonia-fueled planar SOFCs has been developed. The model consists of a planar SOFC cell and fuel/air supply channels. Mass, momentum, energy and charge conservation equations are considered and coupled with the electrochemical reaction of hydrogen and the ammonia decomposition reaction. The ammonia decomposition rate per unit Ni-pore contact area in the Ni-YSZ anodes was developed in the authors’ group and implemented in the numerical model.

Distributions of the physicochemical properties, such as gas concentration, temperature and charge-transfer current, are analyzed and compared between the ammonia-fueled SOFCs and the hydrogen-fueled SOFCs. It was found that in the ammonia-fueled SOFCs the cell temperature first decreased in the upstream region by the endothermic decomposition reaction and then gradually increased towards the downstream, whereas in the hydrogen-fueled SOFCs the cell temperature monotonically increased in the flow direction. Also the peak in the charge-transfer current distribution was shifted towards the downstream in the ammonia-fueled SOFCs because of the altered temperature distribution.