Water Sorption and Diffusion Coefficients of Protons and Water in PVDF-g-PSSA Polymer Electrolyte Mechbranes

摘要

Water sorption properties, proton NMR spectra, and diffusion of water and protons in poly (vinylidene fluroeide)-graft-polystyrene sulfonic acid (PVDF-g-PSSA) polymer electrolyte membranes were studied. Sorption curves for the membranes with different degrees of grafting in protoated and Na~+ form were measured by equilibrating the membranes over saturated salt solutions. The membrane water content was found to be sensitive to changes in relative humidity (RH). The water/sulfonic acid ratio #gamma# for the protonated samples was found 2 at 20% RH andincreased to #gamma# approx 30 at 100%. Proton NMR, pulsed field gradient ptoton NMR (PFG-NMR) and impedance measurements were made on membranes with different #gamma#. In the proton NMR spectra only one pek was found, originating from the water in the membrane. The chemical shift of the peak was found to be dependent on the counterion and the water content. The water self-diffusion coefficents D_H20, measured by PFG-NMR,increased with degree of grafting and water content of the membranes. The proton coductivity and the calculated proton mobility decreased more steply than the D_H20 with decreasing water content.