To investigate the performance of an irreversible direct ammonia-fed solid oxide fuel cell, the direct ammonia-fed solid oxide fuel cell based on oxygen ion conductivity was modeled using finite time thermodynamic theory. First, mathematical expressions for the output power, output efficiency, ecological objective function and ecological coefficient of performance of the direct ammonia-fed solid oxide fuel cell were derived. Further, the effects of parameters such as operating tempera-ture, operating pressure, fuel utilization, and electrolyte thickness on the performance of direct ammonia-fed solid oxide fuel cell were numerically investigated. The results show that as the operating temperature of direct ammonia-fed solid oxide fuel cell increases, the performance of direct ammonia-fed solid oxide fuel cell including output power, output effi-ciency, ecological objective function and ecological coefficient of performance will be improved. Under certain conditions, increasing fuel utilization can improve output power, output efficiency and ecological performance. Increasing the elec-trolyte thickness will decrease the finite time thermodynamic performance of direct ammonia-fed solid oxide fuel cell. Moreover, the microstructure of the electrode also affects the performance of direct ammonia-fed solid oxide fuel cell, and the ecological objective function is increased by 16.9% when the electrode porosity is increased from 0.4 to 0.8.

In order to improve the output performance of direct methanol fuel cell, the finite-time thermodynamic model of direct methanol fuel cell is developed in this paper. Then, mathematical expressions for energy efficiency, power density, exergy efficiency and exergy coefficient of performance are derived. In addition, the effects of operating temperature, inlet pres-sure and membrane thickness on the performance of direct methanol fuel cells are considered. The results show that the exergetic performance coefficient not only considers the exergy loss rate to minimize the loss, but also the power density of the direct methanol fuel cell to maximize its power density and improve its efficiency. Therefore, the exergetic perfor-mance coefficient is a better performance criterion than conventional power and efficiency. In addition, increasing the inlet pressure and decreasing the membrane thickness can significantly improve the exergetic performance coefficient and en-ergy efficiency.