An analysis of the water transport properties of polymer electrolyte membrane

Water transport resistance through the polymer electrolyte membrane was evaluated by measuring the water permeability of it. From the results of a thickness sensitivity evaluation, two types of water transport resistance were found. One was "internal diffusion resistance," which was proportional to the membrane thickness, and the other was "interfacial transport resistance," which was independent of thickness. This interfacial resistance was found not to be negligible. Furthermore, both resistances showed sensitivity to temperature and relative humidity. The internal diffusion coefficient estimated from the results of water permeation experiments correlated well with the results obtained by the pulse field gradient nuclear magnetic resonance (PFG-NMR) method. And, the electro-osmotic drag coefficient was also measured by the proton pump balance method based on the water permeation test system⁽¹⁾. It was concluded that water permeation experiments are helpful for obtaining a better fundamental understanding of water transport mechanism through the membrane.