Abstract
Electrospinning was employed to fabricate composite membranes containing perfluorosulfonic acid (PFSA) ionomer, poly(vinylidene fluoride) (PVDF) reinforcement and a sulfonated silica network, where the latter was incorporated either in the PFSA matrix or in the PVDF fibers. The best membrane, in terms of proton conductivity, was made by incorporating the sulfonated silica network in PFSA fibers (Type-A) while the lowest conductivity membrane was obtained when sulfonated silica was incorporated into the reinforcing PVDF fibers (Type-B). A Type-A membrane containing 65 wt.% PFSA with an embedded sulfonated silica network (at 15 wt.%) and with 20 wt.% PVDF reinforcing fibers proved superior to the pristine PFSA membrane in terms of both the proton conductivity in the 30–90% RH at 80 °C (a 25–35% increase) and lateral swelling (a 68% reduction). In addition, it was demonstrated that a Type-A membrane was superior to that of a neat 660 EW perfluoroimide acid (PFIA, from 3M Co.) films with respect to swelling and mechanical strength, while having a similar proton conductivity vs. relative humidity profile. This study demonstrates that an electrospun nanofiber composite membrane with a sulfonated silica network added to moderately low EW PFSA fibers is a viable alternative to an ultra-low EW fluorinated ionomer PEM, in terms of properties relevant to fuel cell applications.
Highlights
One of the key challenges for proton-exchange membrane (PEM) fuel cell development is the fabrication of a membrane with high proton conductivity for a wide range of relative humidity (RH), while having good mechanical strength, and low in-plane selling [1,2,3,4]
This study demonstrates that an electrospun nanofiber composite membrane with a sulfonated silica network added to moderately low equivalent weight (EW) perfluorosulfonic acid (PFSA) fibers is a viable alternative to an ultra-low EW fluorinated ionomer PEM, in terms of properties relevant to fuel cell applications
Had a PFSA-SiOx SO3 H matrix with an embedded network of uncharged poly(vinylidene fluoride) (PVDF) reinforcing nanofibers, (2) Membrane Type-B was made with a PFSA matrix having an embedded network of reinforcing fibers composed of PVDF-SiOx SO3 H, (3) Membrane Type-C consisted of a PFSA
Summary
One of the key challenges for proton-exchange membrane (PEM) fuel cell development is the fabrication of a membrane with high proton conductivity for a wide range of relative humidity (RH), while having good mechanical strength, and low in-plane selling [1,2,3,4]. The benchmark membrane materials for H2 /air fuel cells are perfluorosulfonic acid (PFSA) ionomers, e.g., Nafion® from Chemours and Aquivion® from Solvay [5] Membranes fabricated from these ionomers have been shown to exhibit high proton conductivity at 100% relative humidity, as well as good chemical and mechanical stability during fuel cell operation. These outstanding properties arise from the superacidity of sulfonic acid fixed-charge groups (in the terminal positions on ether-linked side chains), the semi-crystalline nature of moderate/high equivalent weight (EW) PFSAs, and the nano-phase segregated morphology under hydrated conditions, where ionic clusters aggregate to form water channels which are separated from the hydrophobic polytetrafluoroethylene backbone domains [6,7].
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