Design Of Core-shell Structure SPEEK Fibers And Proton Exchange Membranes By Coaxial Electrospinning

Proton exchange membrane?PEM?is critical component of proton exchange membrane fuel cell.The commercial Nafion membrane usually suffers from high cost and serious methanol crossover.Non-fluorinated sulfonic acid membranes have low cost,however,it's difficult to form connected proton conductive channels.The conductivity is greatly affected by sulfonation degree?DS?,but higher DS can cause excessive swelling and fuel crossover.Therefore,it's necessary to design interconnected proton conductive channels to balance the contradiction between proton conductivity and stability of non-fluorinated sulfonic acid membrane.The network structure of nanofibers prepared by electrospinning can improve the mechanical property and swelling resistance.Driven by the shear force of electric field,the ionic groups aggregate along nanofibers which have oriented ionic morphology to form long-range connected proton conductive channels.Coaxial electrospinning can adjust the composition of core and shell solutions to form core-shell structure fibers.In this paper,different core-shell structures fibers are designed and prepared through coaxial electrospinning,and the comprehensive properties are improved by cooperative utilization of core and shell materials.Firstly,using sulfonated poly?ether ether?ketone?SPEEK?as substrate,the core-shell structure nanofibers are prepared by coaxial electrospinning.The effects of concentration,voltage and receiver rotation speed on the morphology and diameter distribution of fibers are investigated.The optimum conditions of coaxial electrospinning are determined as follows:concentration 20 wt%and voltage 26 k V.On the one hand,for inorganic doped membranes,sulfonated graphene oxide?SGO?/SPEEK core-shell fibers are designed and prepared by coaxial electrospinning.SGO is confined to the SPEEK nanofiber to improve the compatibility and form water-retaining microcapsule,promoting the proton conduction of hopping.During the operation of fuel cell,protons conduct along the thickness of membrane,so the SGO/SPEEK co-spun thickness aligned membrane is prepared,with the consistent fibers'orientation and thickness direction,constructing long-range connected proton conductive channels to improve the proton conductivity.At 80 ^oC,the in-plane and through-plane conductivity of co-spun thickness aligned membrane are 1.2 folds and 1.4 folds those of co-spun surface aligned membrane,and the maximum power density?296.4 mW/cm²?is 1.1 folds and 1.2 folds that of co-spun surface aligned membrane and uni-spun surface aligned membrane,with swelling ratio being kept below 20%.On the other hand,for organic membranes,core-shell fibers of different DS are designed by coaxial electrospinning to take advantages of intrinsic properties of SPEEK adequately.The compatibility is improved by the same kind of material?SPEEK?,with swelling-resistant material?low DS?placing on core layer to form intensive and support skeleton,and high-SO₃H density material?high DS?placing on shell layer to facilitate the aggregation of-SO₃H and the surface proton conduction.This membrane can take advantages of the small size effect of nanofibers and the construction of connected proton conductive channels synergistically to improve the overall performances.At 80 ^oC,the swelling ratio of co-spun?DS core 50%,shell 67%?membrane reduces by 27.4%and 23.9%compared to co-spun?DS core 67%,shell 50%?membrane and co-spun?DS50+67%?membrane,respectively.The conductivity?222.7 mS/cm?is 1.5 folds as high as Nafion 115,and the power density reaching 454.2 mW/cm² is the highest,being 1.3 folds that of Nafion 115.