Dynamic Modeling of Water Sorption in PEM Fuel Cells

This paper compares two models of dynamic water sorption in Nafion^® membranes of polymer electrolyte fuel cells. The first sorption model, commonly used in fuel cell modeling, is based on an assumption of perpetual equilibrium between the membrane water and water vapor at all membrane/vapor interfaces. The second approach, based on non-equilibrium dynamics, assumes that the rate of water sorption in the membrane is proportional to the difference between its actual water content and the equilibrium value. Results show that the steady state membrane water concentration gradient is lower in the equilibrium model, which means that it underestimates the cathode side flooding and anode side dehydration phenomena, compared with the nonequilibrium model. The transient response to changes in cathode humidification is also shown to be significantly different under both models.