Degradation of Perfluorosulfonic Acid Membrane Water Permeance via Formation of Sulfonic Acid Anhydrides

Six perfluorosulfonic acid (PFSA) membranes were subjected to hygrothermal aging at 95 {degree sign}C and monitored by FTIR to assess the rates and extent of ionomer cross linking to the sulfonic anhydride form. Anhydride formation was observed to occur for all PFSA membrane structures studied. The rates of transformation were found to be strong functions of relative humidity, air flow and membrane thickness. Several membrane properties including water permeance, conductivity, and IEC were correlated with the extent of the cross linking reaction.