Potential use of short fibers in Nafion membrane for fuel cell applications

The aim of the present study is to reduce the tortuosity of proton conductive paths within the polymer electrolyte membranes (PEMs). For this purpose, for the first time micro size chopped fibers (modified glass wool fibers), modified nano-silica particles, and a deep eutectic solvent (DES) as electrolyte for anhydrous conditions were incorporated into the Nafion matrix. The measurements showed super proton conductivity beyond ۱۴۰۰ mS/cm at ۱۰۰ ℃ and anhydrous conditions for the Nafion/DES composite membrane containing ۵ wt% short fibers and ۲ wt% nano-silica. Furthermore, the fuel cell performance of the prepared membranes shows promising results by providing a maximum power density of ۷۱۵ mW/cm۲ at ۹۵ ℃. The presence of nano-silica along with short fibers have provided interconnected diffusion pathways within the Nafion membrane. This study clearly shows the important role of ionic paths within the PEMs to achieve desirable properties in the real condition of a fuel cell system.By increasing global warming and air pollution due to excessive consumption of fossil fuels, development of sustainable and reliable clean energy sources is the basic needs of current world [۱]. The long length and polar surface of short glass fiber could provide contentious interface within the polymer matrix which are suitable sites for accumulation of conductive sites of PEMs.The Nafion solution (۵ % in lower aliphatic alcohols and water) was obtained from Iran Polymer and Petrochemical Institute. Glass wool fibers were mechanically cut to short fibers. Short fibers and nano-silica were treated in sulfonic acid solution at high temperatures. The membranes were prepared by solution casting method and were annealed at high temperature (about ۱۳۰ ℃).Based on the obtained results for the modified Nafion membranes in this study at moderate temperature (۱۰۰℃), proton conductivity of ۱۴۲۶ mS/cm was attained. Fig. ۱ (a) displays interesting results for NF۵M-۲ sample (containing ۵ wt% fiber and ۲ wt% nanosilica), so that a maximum power density of ۷۱۵ mW/cm۲ was obtained at ۹۵℃. Also, the temperature has a positive effect on its fuel cell performance, in a way that by increasing temperature from ۶۰ ℃ to ۹۵ ℃ about ۸۶ % increase in its maximum power density was obtained Figure ۱. Polarization curves for H۲/O۲ fuel cell system using (a) NF۵M-۲ sample at different temperatures and anhydrous condition, (b) NF۵M-۲ and pure recast Nafion membranes at anhydrous condition, (c) NF۵M-۲ sample at anhydrous condition and commercial Nafion ۱۱۵ and Nafion ۱۱۷ at fully hydrated condition and ۸۰ ℃, and durability test under OCV and constant ۰.۳ A/cm۲ current (d).Potential use of modified short fibers for development of ionic path within the Nafion membrane was evaluated. The obtained results showed that such reinforcements have caused superior properties for Nafion/DES composite membranes for application in anhydrous fuel cells

Keywords:

Nafion , Fuel cells , Proton conductivity , Deep eutectic solvents