Steady and unsteady 3D non-isothermal modeling of PEM fuel cells with the effect of non-equilibrium phase transfer

A 3D model that fully couples multi-species and multi-phase transport, electrochemical kinetics, and heat transfer processes has been developed. The non-equilibrium membrane water absorption/desorption processes along with non-equilibrium condensation/evaporation processes have been investigated utilizing this comprehensive model. In addition, the fallacious assumption that water is produced in vapor phase during the half cell electrochemical reaction is addressed for the first time. The difference and relationship of the cell output current density among three water production mechanisms are exhibited to show the potential error induced by vapor or liquid production assumptions. The present model is capable of predicting transient phenomena within the cell as well. Our results show that compared to the liquid production modeling the dynamic response of PEM fuel cells in vapor production modeling is significantly overestimated owing to the sluggish condensation process.