Influence of membrane properties on the transient behavior of polymer electrolyte fuel cells

Understanding the performance of proton exchange membrane (PEM) fuel cells is critical to the water management in the fuel cell system. Low-humidity operating conditions present a complex interaction between dynamic behavior and water transport owing to different time scales of water transport mechanisms in the transient process. Toward understanding the effects of membrane properties on the dynamic behavior, this paper presents numerical simulations for a single channel PEM fuel cell undergoing changes in load, by subjecting the unit cell to step change in current. The complex interaction between cell voltage response and water transport dynamics for various membrane properties is explored in detail, where the performance is critically related to the water content of the membrane. Detailed computational fluid dynamics (CFD) simulations are carried out to show that step increase in current density leads to anode dryout due to electro-osmotic drag, and to investigate the dependence of transient behavior on the variations in membrane properties. The results show that water uptake by the membrane is a crucial factor in determining the occurrence of anode dryout and hence voltage reversal, and can be avoided by a graded membrane design.