Properties Of Nafion/PVDF Coaxial Fiber Proton Exchange Membranes

The proton exchange membrane is a solid electrolyte material in a proton exchange membrane fuel cell（PEMFC）,which acts to isolate the bipolar fuel and provide a proton transport channel for the bipolar.It should have compactness,high proton conductivity,strong mechanical properties and swelling resistance.The commercialized perfluorinated proton exchange membrane Nafion has insufficient mechanical properties and swelling resistance,and is expensive.Non-fluorinated or non-perfluorinated proton exchange membranes have problems such as low proton conductivity or compatibility.In this paper,coaxial electrospinning method is proposed to design Nafion/PVDF coaxial fiber composite membrane,Nafion fiber shell layer builds long-range proton conduction channels and high conductivity,PVDF core layer provides strong mechanical properties and anti-swelling properties,coaxial fiber confinement effect and The bonding of Nafion components in the core layer fibers enhances the interfacial bonding between Nafion and PVDF.Compared with the blended cast membrane and the uniaxial electrospun membrane,the coaxial electrospun membrane has significantly improved tensile strength,reduced swelling,and improved battery performance.First,the spinnability,mechanical properties,swelling resistance and oxidative stability of the reinforcing material polytetrafluoroethylene（PTFE）and polyvinylidene fluoride（A-PVDF and S-PVDF）of different manufacturers were compared.PTFE membrane has the best oxidative stability,but poor spinnability,and cannot be hot-pressed to form a dense membrane.The morphology of the 10 wt%A-PVDF fibers was incomplete,and the average diameter of the 14 wt%A-PVDF fibers was too large（1.18μm）.The mechanical properties of the S-PVDF electrospun membrane are the best,with the maximum stress and strain of 37.4MPa and 137.6%,respectively,which are 13.0%,39.0%and 144.4%,73.7%higher than that of the A-PVDF electrospun membrane and the PTFE electrospun membrane,respectively..Therefore,10 wt%S-PVDF was selected as the core reinforcement material of the coaxial fiber proton exchange membrane.Then,by coaxial electrospinning,a coaxial electrospun Nafion/PVDF proton exchange membrane with a coaxial fiber structure was constructed.The average fiber diameter of Co-NP is 300 nm,which is 57.9%larger than that of Un-NP.The swelling degree of the coaxial fiber membrane is 10.8%,which is only half of that of the cast membrane.The coaxial fiber membrane has the best tensile resistance,and the maximum tensile deformation is as high as 147.2%,which is 29.5%higher than that of the uniaxial fiber membrane.At80°C,the peak power density of the coaxial fiber membrane battery is 826.4 m W cm^-2,which is 58.4%and 10.0%higher than that of the cast membrane and uniaxial fiber membrane battery,respectively.Finally,the core and shell components Nafion and PVDF of the coaxial fibers were optimized.Co-PVDF@9:1-Shell,Co-3:7@9:1-Shell and Co-11:9@Nafion-Shell membranes were prepared.The oxidation stability of the three membranes is higher than that of the commercial Nafion 211 membrane,and the Co-PVDF@9:1-Shell membrane has the highest oxidation stability,with a mass loss of 1.3%after soaking in Fenton’s reagent at 80°C for 4 h,18.5%and 62.5%less mass loss than Co-3:7@9:1-Shell and Co-11:9@Nafion-Shell membranes,respectively.The Co-3:7@9:1-Shell membrane exhibits the best mechanical properties,and its maximum stress and strain are 211.6%and 5.4%higher than those of Nafion 211,respectively.At 80°C,the proton conductivity of Co-11:9@Nafion-Shell membrane is 22.0%higher than that of Nafion 211,and the peak power density is 1119.2 m W cm^-2,which is 6.8%higher.