Preparation And Properties Of PVDF-Nafion Core-shell Nanofiber

The development of high-performance,low-cost proton exchange membranes is a prerequisite for the large-scale application of proton exchange membrane fuel cells.Nafion membrane is the most used proton exchange membrane for proton exchange membrane fuel cells.The traditional Nafion membrane has the disadvantages of high raw material cost,large swelling degree after water absorption,and poor mechanical properties.In recent years,Nafion fiber proton exchange membranes with high specific surface area,porosity,mechanical properties,and proton conductivity have attracted the attention of researchers.PVDF has good chemical resistance.Adding PVDF to Nafion can improve its dimensional stability,mechanical properties,and barrier properties,but will lead to a significant decrease in proton conductivity.In this paper,PVDF-Nafion core-shell nanofibers are mainly prepared by coaxial electrospinning technology.By optimizing the PVDF content and adjusting the electrospinning parameters,PVDF-Nafion core-shell fiber proton exchange membranes with high proton conductivity,excellent mechanical properties,and low cost are obtained.The paper firstly investigated the effect of solvent on electrospinning of Nafion solution.High-purity Nafion-ethanol fiber proton exchange membrane and NafionDMF fiber proton exchange membrane were prepared by electrospinning technology with ethanol-water and DMF as a solvent and high molecular weight PEO as an additive,respectively.Compared with the Nafion 117 membrane,the proton conductivity of the Nafion-ethanol fiber proton exchange membrane at 70 ℃ increased from 0.1230 S/cm to 0.2179 S/cm,the water absorption increased from 31.5% to 59.75%,the swelling degree increased from 22.67% to 30.31%,the tensile breaking strength decreased from11.88 Mpa to 5.49 Mpa,and the excessive water absorption resulted in the poor dimensional stability and mechanical properties.The Nafion-DMF fiber proton exchange membrane has lower water absorption and proton conductivity than the Nafion 117 membrane and higher dimensional stability of 10.75% and mechanical properties 14.20 Mpa.Then,six kinds of Nafion/PVDF(N/P)fibers with different PVDF contents were prepared by electrospinning technology,and their proton exchange membranes with low cost,high proton conductivity,excellent dimensional stability,and mechanical properties were obtained.The diameter of N/P nanofibers increased with the increasing PVDF content.The water absorption,swelling degree,and proton conductivity of the N/P fiber proton exchange membrane are inversely proportional to the PVDF content,and the mechanical properties are proportional to the PVDF content.Compared with the Nafion 117 membrane,the water absorption and swelling degree of N/P-0.2 fiber proton exchange membrane with the 16.67% PVDF content decreased to 9.17% and13.12%,respectively,and the tensile breaking strength increased by 60% to 18.93 Mpa.When the PVDF content is less than 25.93%,the proton conductivity of N/P fiber proton exchange membrane at 70 ℃ is higher than that of the Nafion 117 membrane.When the PVDF content increased to 33.33%,the proton conductivity of the N/P fiber proton exchange membrane decreased rapidly and was lower than that of the Nafion117 membrane.Finally,using coaxial electrospinning technology,PVDF-Nafion and PVDF-N/P core-shell fiber proton exchange membranes were prepared by using PVDF solution as core and high-purity Nafion solution and N/P(1:4)solution as shell,respectively.The swelling degrees of the two core-shell fiber proton exchange membranes were 9.38%and 6.64%,respectively,showing excellent dimensional stability,and the tensile breaking strengths were both greater than 50 Mpa.At 70 ℃,the proton conductivity of PVDF-Nafion core-shell fiber proton exchange membrane is 0.09 S/cm,higher than that of PVDF-N/P,and 73.17 percent of that of Nafion 117 membrane,whereas the proton conductivity of the N/P-0.5 fiber proton exchange membrane with 66.67%Nafion content is only 27.32% of the Nafion 117 membrane.The PVDF-Nafion coreshell fiber proton exchange membrane exhibits excellent proton conductivity,mechanical properties as well as lower raw material cost.