Properties of stretched 830 EW Aquivion

Abstract

Elongated 830 equivalent weight (EW) Aquivion® (a perfluorosulfonic acid polymer with an ion exchange capacity of 1.2 mmol/g) was investigated for potential use in direct methanol fuel cells by determining the effect of uniaxial stretching on polymer crystallinity, proton conductivity, methanol permeability, water uptake, and mechanical strength. Stretching Aquivion® at 190°C to a draw ratio of six creates a 15% increase in crystallinity. This change crystallinity is accompanied by improvements in mechanical properties as evidenced by an enhanced Young’s modulus, plastic modulus, and ultimate stress during tensile stress measurements. Additionally, when compared to unstretched solution-cast Aquivion®, stretched Aquivion® with a draw ratio of six shows a 7% increase in proton conductivity (in water at 25ºC), and a 63% and 72% decrease in methanol permeability at 25°C and 60ºC respectively, for a 1 M methanol solution. The decoupling of methanol permeability and proton conductivity was observed previously in stretched recast Nafion® (a perfluorosulfonic acid membrane with an ion-exchange capacity of 0.91 mmol/g). The methanol fuel cell properties of stretched Aquivion® at a draw ratio of six all surpass those obtained for commercial Nafion® 117 (the current DMFC benchmark membrane) under the same testing conditions. It can be concluded from the present work that stretching a solution cast Aquivion® film significantly enhances key membrane properties that should translate into better direct methanol fuel cell operation.