Two-phase modeling and flooding prediction of polymer electrolyte fuel cells

A newly developed theory of liquid water transport in hydrophobic gas diffusion layers is applied to simulate flooding in polymer electrolyte fuel cells (PEFCs) and its effects on performance. The numerical model accounts for simultaneous two-phase flow and transport of species and electrochemical kinetics, utilizing the well-established multiphase mixture formulation to efficiently model the two-phase transport processes. The two-phase model is developed in a single domain, yielding a single set of governing equations valid in all components of a PEFC. The model is used to explore the two-phase flow physics in the cathode gas diffusion layer. Multidimensional simulations reveal that flooding of the porous cathode reduces the rate of oxygen transport to the cathode catalyst layer and causes a substantial increase in cathode polarization. Furthermore, the humidification level and flow rate of reactant streams are key parameters controlling PEFC performance and two-phase flow and transport characteristics. It is also found that minimization of performance limitations such as membrane dry-out and electrode flooding depends not only on material characteristics but also on the optimization of these operating parameters. (C) 2005 The Electrochemical Society. All rights reserved.