A detailed model of a PEMFC is developed considering the effect of liquid water in all the layers of cathode (namely gas flow channel, back up substrate, diffusion layer and catalyst layer). The catalyst layer is characterized through a spherical flooded agglomerate approach in line with experimental evidence. A thin film of ionomer is considered on top of the spherical agglomerate. It is assumed that the water produced in the reaction sites diffuses to the surface of the agglomerate forming a thin film before undergoing evaporation/condensation process. An effectiveness factor approach is adopted to calculate the rate of oxygen reduction reaction. Cathode experimental data for a wide range of flow rates are used to validate the model. The simulation results and the validation with the experimental data depends heavily on the liquid water saturation related boundary conditions. The boundary conditions for liquid water saturation are not well discussed in the existing literature. Depending on the wettabilities of the different materials and the operating conditions, the saturation may vary widely at the boundary. We propose a set of possible boundary conditions in order to capture the physics of the liquid water at the interphase. The model captures the effect of the change in the interphase saturation on the performance of the cell. With the change in the contact angle on the surfaces, the driving force for liquid water flow will also vary significantly affecting the cell power density. Several sensitivity studies will be discussed to assess the impact of the underlying assumptions. The simulations clearly show that the interfacial liquid coverage plays a very important role in determining the limiting current density of the cell in a given operating condition. The use of this model in design and optimization studies will also be outlined.

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