Nanofiber composite membranes with low equivalent weight perfluorosulfonic acid polymers

Abstract

Two low equivalent weight perfluorosulfonic acid (PFSA) polymers (825 EW and 733 EW) were successfully electrospun into nanofibers by adding as little as 0.3 wt% of high molecular weight poly(ethylene oxide) as a carrier polymer. The electrospun fiber morphology transitioned from cylindrical filaments to flat ribbons as the total concentration of PFSA + carrier in solution increased from 5 wt% to 30 wt%. PFSA nanofiber mats were transformed into defect-free dense membranes using a four-step procedure: (i) annealing the PFSA polymer during which time intersecting fibers were welded to one another at cross points (ii) mechanically compacting the mats to increase the volume fraction of nanofibers to $75%, (iii) imbibing an inert polymer, Norland Optical Adhesive (NOA) 63, into the mats (to fill entirely the void space between nanofibers) and then crosslinking the NOA with UV light, and (iv) removing the poly(ethylene oxide) carrier polymer by boiling the membrane in 1.0 M H 2 SO 4 and then in deionized water. The resulting membranes exhibited higher proton conductivities than that of commercial Nafion 212 membrane (0.16 S/cm at 80 C and 80% relative humidity and 0.048 S/cm at 80 C and 50% relative humidity for a membrane with 733 EW nanofibers), with low water swelling (liquid water swelling of 18% for membrane with high conductivity). The proton conductivity of both EW nanofiber composite membranes increased linearly with the PFSA nanofiber volume fraction, whereas gravimetric water swelling was less than expected, based on the volume fraction of ionomer. There was a significantly improvement in the mechanical properties of the nanofiber composite membranes, as compared to recast homogeneous PFSA films.

Effects of ethanol and isopropanol on the structures and properties of polyethersulfone/perfluorosulfonic acid nanofibers fabricated via electrospinning

“…Nah et al [10] reported a three times enhancement of the ionic conductivity as comparing the electrospun Nafion nanofiber membranes with dense films, while Dong's [8] research demonstrated that a further improvement could be achieved up to an order of magnitude higher if high-purity Nafion was employed. Furthermore, Choi et al [11] fabricated nanofiber membranes successfully with PFSA and 0.3 wt.% high molecular weight PEO, and these membranes exhibited higher proton conductivities than that of commercial Nafion 212 membranes. Many of these works, however, only focused on the factors associated with polymer composition in blend solutions such as the type of carrier polymer, polymer concentration as well as the ratio of polymer to PFSA resin.…”

Anion exchange membranes from hot-pressed electrospun QPPO–SiO2 hybrid nanofibers for acid recovery

“…Recently, the electrospinning process has attracted wide attentions in fabricating membranes, which fabricates nanofibers with porous morphology and large specific surface area [18][19][20][21]. Through a simple hot-press treatment, the corresponding membranes can be formed and tend to be dense in macroscopic scale but loose in microscopic scale.…”

Silicon carbide fiber-reinforced composite membrane for high-temperature and low-humidity polymer exchange membrane fuel cells

“…Electrospun membranes have been widely investigated in several areas, such as lithium secondary batteries, biomedical materials, filters, and clothing to protect against electromagnetic waves, sensors, radioactive radiation, and electronic devices [16e19]. Up to now, however, there have only been a few reports on PEMs based on the electrospinning method [20,21]. Electrospun PEMs with good stability and high performance in high temperature conditions have not yet been reported, to the best of the authors' knowledge.…”