(564d) A Steady State Three-Dimensional Model for a Pemfc System

The automotive industry is making progress toward development and commercialization of PEM fuel cells. PEM fuel cells (PEMFC) are an attractive alternative for the internal combustion engine in automotive applications because they are cleaner and more fuel-efficient. More importantly, automotive fuel cells enable the goals of reduced-dependence-on-oil and transition to a hydrogen economy. In order to successfully design PEMFC systems for these applications development of a thorough understanding of various phenomena that occur during the operation of these systems is needed. Mathematical modeling can be used to improve the understanding of these systems and to help improve the design of these systems.

In this work, a steady state three-dimensional mathematical model that accounts for the coupling between transport phenomena, phase change, and fuel cell electrochemistry in a PEMFC stack is presented. The model captures the effect of multi-component diffusion of gases between the gas channels and the catalysts through the porous layers of the fuel cell using Stefan-Maxwell equations. Pore-flooding as a function of the capillary pressure in each of the porous layers of the unitized electrode assembly is modeled. Water transport through the porous layers is modeled using Darcy's Law. Water transport through the ionomer in the membrane and the catalyst layers is modeled by a combination of pressure driven flow, electro-osmotic drag, and concentration gradient driven back diffusion. The hydrogen oxidation reaction and the oxygen reduction reaction in the catalyst layers is modeled using Butler-Volmer kinetics. In the gas channels the pressure drop associated with two-phase flow is also modeled. This model architecture allows the capability to simulate both single cell and stack systems. Through simulations of this model the effect of different operating conditions ? relative humidity, temperature, and pressure of the gases ? and system parameters ? membrane thickness, gas channel design, etc. ? on water management and steady state performance of the fuel cell can be studied. Results from these simulations will also be presented and discussed.