Water permeation through polymer electrolyte membranes

Water management has a major impact on the performance of the polymer electrolyte membrane fuel cells. An understanding of water permeation through polymer electrolyte membranes is crucial to offset the unbalanced water activity within fuel cells. The work presented in this thesis includes contributions that provide insight into internal and interfacial water permeation behavior of membranes, as well as insight into how membranes could be designed to enhance water management. Three types of ex-situ water permeation techniques are used in this thesis work. These are: liquid-liquid water permeation (LLP) in which both sides of the membrane are in contact with liquid water; liquid-vapor permeation (LVP) where one side of the membrane is exposed to liquid, and the other is exposed to vapor; and vapor-vapor permeation (VVP) where both sides of the membrane are exposed to water vapor. Three polymer electrolyte membrane systems were investigated under varied experimental conditions: degraded Nafion®, short side chain (SSC) perfluorosulfonic acid ionomer membrane, and an emerging class of anion exchange membrane, poly(benzimidazolium). Correlations between membrane series were drawn and compared to the commercially-available materials. It was found that membranes of smaller thickness, greater water volume fraction (Xv), and higher ion exchange capacity (IEC) result in a higher overall water permeability. However, the membrane thickness, Xv, and IEC do not dominate the rate of water permeation through the membrane interface. In contrast, the side chain length of the polymer is found to influence the interfacial water permeation, wherein membranes with longer side chain length are more water permeable at the interface.