The kinetics of water sorption in Nafion membranes: a small-angle neutron scatteringstudy

Abstract

The optimization of the water management in proton exchange membrane fuel cells is amajor issue for the large-scale development of this technology. In addition to the operatingconditions, the membrane water sorption and transport processes obviously control thewater management. The main objective of this work is to provide new experimentalevidence based on the use of the small-angle neutron scattering (SANS) technique in orderto allow a better understanding of water sorption processes. SANS spectra were recordedfor membranes equilibrated with either water vapor or liquid. Sorption kinetics data weredetermined and the SANS spectra were analyzed using the method developed forextracting water concentration profiles across the membrane in operating fuelcells. The water concentration profiles across the membrane are completely flat,which indicates that the water diffusion within the membrane is not the limitingprocess. This result provides new insight into the numerous data published on theseproperties. For the first time, the swelling kinetics of a Nafion membrane immersed inliquid water is studied and a complete swelling is obtained in less than 1 min.