(193l) High Production Rate of Nafion Nanofibers Via needleless Electrospinning

Nafion, a perfluorinated anionic (sulfonic acid) polymer, possesses excellent thermal, mechanical, and chemical stability, along with high water-saturated proton conductivity (~0.1 S/cm), and therefore has been explored in various applications, including water electrolysis, chlor-alkali electrolyzers, sensors, superacid catalysts, and most notably as a polymer electrolyte membrane and ionomer in hydrogen fuel cells. Nafion is commercially available in several forms, including extruded and solution cast films, dispersions in water/alcohol solvents, and pellets. Recently, studies have shown that Nafion can be produced in nanofiber form through electrospinning and the resulting nanofibers exhibit enhanced properties, such as super proton conductivity (>1 S/cm) and excellent platinum utilization (0.076 g/kW) when used in fuel cell electrodes. These enhanced properties along with possible other new enhanced properties, such as self-healing and shape memory retention, could broaden the impact and range of applications for Nafion. However, it is challenging to electrospin high purity Nafion nanofibers using conventional needle electrospinning techniques due to the lack of polymer chain entanglement in solution (due to ionic aggregation) limiting needle electrospinning to narrow solution concentration ranges and requiring the addition of carrier polymers. Additionally, needle electrospinning results in low nanofiber production rates. Numerous needleless electrospinning techniques have been developed and explored to increase the production rate of polymer nanofibers. However, almost all needleless electrospinning techniques produce lower fidelity nanofibers compared to needle electrospinning and no study has demonstrated the needleless electrospinning of Nafion. In this study, a needleless electrospinning process was developed to fabricate and increase the production rate of high purity, high fidelity Nafion nanofibers. This needleless electrospinning process generates ~100-1000 electrospinning sites that promote chain entanglement for facile electrospinning due to the locally higher polymer concentration at thin film solution sites. Results demonstrate similar fiber diameter sizes when comparing nanofibers produced from needleless and needle electrospinning (233 ± 62 and 216 ± 69 nm diameters, respectively), demonstrating the ability to produce high fidelity Nafion nanofibers with needleless electrospinning. Additionally, high purity Nafion nanofibers (98 wt% Nafion) were produced at higher polymer concentrations with needleless electrospinning compared to needle electrospinning. Furthermore, the production rate of Nafion nanofibers increased by an order of magnitude when comparing needleless to needle electrospinning (1.0 versus 0.1 mg/h). Therefore, this needleless electrospinning process can not only produce high purity, high fidelity Nafion nanofibers at high production rates, but also provides a platform to investigate the polymer physics of Taylor cone formation under an applied electric field for charged polymers at thin film solution surfaces.