Modeling water uptake of proton exchange membranes
P.Berg and K. Promislow
Simon Fraser University, CA
Keywords: PEM Fuel cell
Water content in Nafion membranes of proton exchange membranes (PEM) is crucial to its functionality. The adsorption of liquid water occurs on a time scale of seconds, while the desorption (drying) time scale is on the order of hours. In this contribution, we show that these disparate phenomena can be modeled by the same nonlinear diffusion model. Two essential ingredients to match experimental results are: 1) a diffusion coefficient that varies dramatically across the water content regime of interest; 2) a boundary condition that couples the water flux at the interface to the water content of the membrane and the sorption equilibrium prescribed by the environment. We demonstrate that the hydration-dehydration dichotomy arises from an intrinsic hysteresis implicit in the nonlinear model.
NSTI Nanotech 2003 Conference Technical Program Abstract