An Empirical Model for the Flooding Behavior of Ultra-thin PEM Fuel Cell Electrodes

Abstract

A quantitative empirical model is applied to explain the onset of cathode flooding behavior of PEM fuel cell membrane electrode assemblies having the ultra-thin 3M NSTF (nanostructured thin film) electrocatalysts and first generation Toray carbon paper gas diffusion layers (GDL). An empirical method is used to define the current density at the onset of cathode flooding, and calculated vapor phase water removal rates at specific water balance conditions are found to give excellent quantitative agreement with the measured rates of water generation for three different first generation GDL's. Effective water vapor diffusion coefficients porosites and saturation levels for the GDL's can be extracted from the water balance data at the in-situ operating conditions. Application of the method to later generation GDL's for which the flooding occus at much lower temperatures is also discussed, with the conclusion that liquid phase transport plays a greater role for these GDL's.