Phase Change in a Polymer Electrolyte Fuel Cell

Stable high performance in a polymer electrolyte fuel cell (PEFC) requires efficient removal of product water and heat from the reaction sites. The most important coupling between water and heat transport in PEFC, through the liquid-vapor phase change, remains unexplored. This paper sheds light on physical characteristics of liquid-vapor phase change and its role in PEFC operation. A two-phase, nonisothermal numerical model is used to elucidate the phase-change effects inside the cathode gas diffusion layer (GDL) of a PEFC. Locations of condensation and evaporation are quantified. Operating conditions such as the relative humidity (RH) of inlet gases and materials properties such as the thermal conductivity of GDL are found to have major influence on phase change. Condensation under the cooler land surface is substantially reduced by decreasing the inlet RH or increasing the GDL thermal conductivity. The RH effect is more pronounced near the cell inlet, whereas the GDL thermal conductivity affects the phase-change rate more uniformly throughout the flow length.