Abstract
Fuel cells are considered as major components of the future energy infrastructure in many applications due to their high efficiency, simplicity of operation, scalability, and low pollution. The inherent complexity of the internal operation of fuel cells and limitations in the experimental studies on fuel cells make the numerical simulation a vital tool for the fuel cell research and development. This field has experienced remarkable advancements in the past three decades. A wide variety of modeling approaches have been introduced in the literature. Many mathematical formulations have been employed for the macro-level modeling of solid oxide fuel cells (SOFCs). In this paper, the common fundamental bases behind different modeling approaches are identified and presented. Similarly, many assumptions have been used to simplify the modeling process. Some of the most common assumptions for modeling SOFCs are identified, and their appropriateness is reevaluated in the light of recent advancements in the experimental and numerical findings. It was found that while 0-D models cannot predict the internal dynamics of SOFCs, they are very useful for applications where the objective is to study the interaction among system components, such as SOFC hybrid plants. While several types of fuel reformers have been proposed, the identification of the most efficient technology at the operating conditions of SOFCs, particularly small-size applications, requires more research. Similarly, more research is needed to determine if the direct electrochemical reaction of carbon monoxide can be ignored in SOFC models. On the other hand, it has been experimentally proven that internal fuel reformers are thermally self-sufficient. While the assumption that the steam reforming reaction reaches chemical equilibrium has been supported by several experimental studies, the similar assumption for the water-gas shift reaction is not proven, rather there are some strong evidences against its validity. It is also proven that the methane reforming reaction reaches equilibrium when all the inlet methane moles are consumed. The presented assumptions, mathematical formulations, model constants, system operating parameters, and model validation can assist researchers in making informed decisions on their choices for future SOFC models. Also, it identifies the areas where more research, particularly experimental research, is needed to verify the validity of the assumptions.