Morphology and performance of stretched PFSA for direct methanol fuel cells

Uniaxial stretching was used to promote desirable morphological changes to membranes composed of 3M Corporation's 825 equivalent weight (EW) perfluorosulfonic acid (PFSA) polymer. Stretching of solution cast PFSA films to a draw ratio of 4 was carried out prior to a high temperature annealing step. Film stretching increased the polymer crystallinity by 22% with an improvement in the membrane's mechanical properties. There was a small increase in proton conductivity after stretching, with a substantial decrease in methanol permeability. In direct methanol fuel cell tests at 60°C and 1.0 M methanol, the power density at 0.4 V with a stretched 3M 825 EW membrane was 72 mW/cm2, which was considerably greater that that obtained with a solution cast unstretched membrane (28 mW/cm2) or with a commercial Nafion 117 membrane (55 mW/cm2). ©The Electrochemical Society.