| As a key component of barrier fuel and proton conduction in fuel cell, the proton exchange membrane (PEM) determines the working efficiency and cost of fuel cell. Commercial PEMs, represented by perfluorosulfonic acid membrane Nafion produced by Du Pon, exist some problems, such as low performance under high temperature and low humidity, high permeability and high price. Sulfonated polyether ether ketone (SPEEK) has advantages of low price and high mechanical strength, but the contradiction of degree of swelling and conductivity must be resolved. Doping sulfonated inorganic materials for preparing organic-inorganic composite membrane is one of the ways to suppress membrane swelling, improve proton conductivity and improve methanol prevention. However, conventional casting method has organic-inorganic poor compatibility problem when doping inorganic material. This paper proposes the use of a coaxial co-spinning process to coat the inorganic material inside the electrostatic spun fibers forming the core-shell morphology. The inorganic material is affected by spin orientation so that it is uniformly dispersed in the membrane matrix, thus the macroscopic phase separation in membrane is reduced and methanol prevention is improved; at the same time, proton conductive groups are ordered along the core-shell interface to open up the proton conducting channels in membrane.Firstly, we used the method of silane coupling to functionalize graphene oxide (GO), forming the silane coupling sulfonation of graphene oxide (SSi-GO). The left move of 1130 cm-1 peak due to symmetric and asymmetric vibration of sulfonic acid groups proved successful grafting of sulfonic acid groups. We applied coaxial co-spun to prepare SPEEK coated SSi-GO core-shell structure of electrospun fibers and examined the effect of voltage, viscosity of both inside and outside spinning solution, liquid propulsion rate of both inside and outside spinning solution on fiber morphology and fiber size distribution to determine the optimal spinning conditions:spinning voltage 26kV, viscosity of both inside and outside spinning solution are 561cP, liquid propulsion rate of both inside and outside spinning solution are luL/min. Under these conditions, the resulting composite fiber has centralized diameter distribution, uniform thickness. SSi-GO is coated well, and has certain orientation.Then we used hot pressing method for preparing dense PEM from coaxial spinning fiber and prepared a series of SPEEK/SSi-GO core-shell fiber composite membrane with different doping amount. The surface of composite membrane is substantially retained fiber morphology, the cross section is dense and uniform, no macroscopic phase separation is observed; water absorption and membrane conductivity increases with the doping amount at first and then tends to be the same. The composite membrane with doping amount of 2.5wt% has the best performance, its conductivity reaches 94.6 mS/cm under 30 ?, which is 3.4 times of the SPEEK pure electrospinning membrane.In order to compare the effects of different morphologies of SSi-GO in the membrane on the membrane performance, blend electrospinning and blend casting are used to prepare blend spinning membrane and blend casting membrane with 2.5wt% doping amount. Results of performance tests show that:unlike composite fibers with core-shell structure, SSi-GO floats on the surface of the fiber network in fibers prepared by blend spinning. After the membrane formed, SSi-GO is embedded directly in the membrane, so the compatibility is poor, thus the conductivity of membrane is reduced. The conductivity of the membrane is only half of the common coaxial spinning one; the coaxial doping of SSi-GO greatly enhanced the membrane selectivity (conductivity/methanol permeability), which is about 11 times of Nafionl15; core-shell structure opened a proton-conducting channel, the power density is 3.2 times of the blend spinning membrane,2.2 times of SPEEK pure spinning membrane. |
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