Preparation And Properties Of Nano - Fiber Modified Nafion Composite Proton Exchange Membrane

Proton exchange membrane fuel cell (PEMFC) is a energy conversion device that could convert the chemical energy into electricity, and owe high energy densities, quick start and envirmental friendly advantages. Therefore, PEMFC are considered as a green technology that meets the urgent need of future society. The proton exchange membrane (PEM) is the key component of PEMFC, and it not only acts as an insulator between the fuel, but also transports H+. Its good or bad performance could influce the performance of PEMFC. Perfluorosulfonic acid membranes, such as Nafion, have been extensiveiy used in PEM. However, the drawbacks of perfluorosulfnoated membranes, including high production cost and high permeation rate of methanol, have limited the industrial applications of PEMFC. Therefore, the development of high performance of PEM has been a hot topic. Characteristic of nano-materials could enhanced proton transfer process and mechanical properties. Recently methods for constructing high performance proton exchange membrane have received considerable attentions. This study find a new method for the preparation of high performance PEM by introducing nanofiber to construct one-dimensional proton transfer channels. The main works are mainly as follows:The sulfonated poly(ether sulfone) (SPES)/poly(ether sulfone) (PES) nanofiber mat was fabricated through solution blowing method which is a patent owned by our workgroups, and the Nanofiber/Nafion (NF/Nafion) composite membranes were prepared through impregnation method. The obtained SPES/PES nanofiber with diameter ranged mainly between 300nm-450nm was in three-dimensional crimp state, and its morphology is good. The composite membranes exhibited higher thermal stability, water uptake and proton conductivity compared to Nafion. The existence of nanofiber improved conductivity of membranes. At immersion temperature 80℃, the proton conductivity of NF/Nafion-20 was 0.145 S/cm. The increasing contents of nanofiber contributed to water uptake, while the swelling ratio was smaller. This is because NF skeleton limited the membrane swelling. Meanwhile, the selectivity of the composite membranes were higher than that of Nafion 117, and that of NF/Nafion-20 was9.6×104Sscm-3.Based on the excellent characteristics of SiO2 inorganic materials, such as water retention and thermal stability, the SPES/SiO hybrid nanofibers were fabricated by solution blowing method, then the SPES/SiO2/Nafion composite membranes were prepared through impregnation method. The results showed that the introduction of solution-blown nanofibers to composite membranes improved thermal stability, water uptake and dimensional stability of Nation. At immersion temperature 80℃, the proton conductivity of SPES/SiO2/Nafion-15 was 0.154 S/cm. The introduction of SiO2 could decrease the methanol permeability of composite, and the methanol permeability of hybrid membrane was lower than that of Nafion and SPES/PES/Naifon membrane, and that of SPES/SiO2/Nafion-25 was 6.3×10-7 cm2/s.The protein plays an important role in the process of proton transport in the organism. Inspired by this, we prepared SiO2 nanofiber by electrospinning, and modified SiO2 nanofiber with cysteine, lysine, serine, and glycine through carboxyl functionalization and amino acid fixation. In order to increase the transportation sites of H+ in the composite membrane, and improve proton conductivity of the composite membrane, the amino acid molecules were introduced into the fiber surface. The results showed that the length of the amino acids molecular chain has no effect on the water uptake, swelling ratio and proton conductivity of the composite membrane, but it can affect the diameters of the nanofibers. Longer the amino acid molecules chains are, larger the diameters of the nanofibers are. The number and the polarity of polar groups have a great influence on the properties of the composite membranes. The larger number and stonger of polar groups could increase water uptake and proton conductivity of membrane. The variation of water uptake is that Nafion-Cys> Nafion-Ser>Nafion-Lys>Nafion-Gly>Nafion, and the water uptake influence the swelling ratio. Then the variation of swelling ratio is that Nafion>Nafion-Cys> Nafion-Ser>Nafion-Lys>Nafion-Gly. Because of the difference of the number of the transportation sites of H+ represented by amino acid molecules, the variation of proton conductivity is that Nafion-Cys> Nafion-Ser>Nafion-Lys>Nafion-Gly>Nafion.