Research On Nanofiber Structural And Functional Design And The Preparation And Performance Of Composite Proton Exchange Membranes

Proton exchange membrane fuel cell（PEMFC）is an advanced renewable energy conversion device that directly converts chemical energy in fuel（hydrogen or methanol）into electrical energy.It has gained widespread attention due to its high safety,simple structure design,and high power density,among other advantages.Proton exchange membrane（PEM）is the core component of PEMFC,which separates oxidants and reductants while conducting protons.The performance of PEM directly determines the performance of PEMFC during actual operation.Constructing long-range continuous proton conduction channels within the PEM is the main method for improving its proton conduction performance.In recent years,constructing proton transfer channels through one-dimensional nanofiber hybridization has become the main technical means for researchers.Protons can accumulate along the radial direction of electrospun nanofibers,forming long-range interconnected proton conduction channels,thereby achieving high-speed proton conduction.From the perspective of fiber structure and functional design,this article presents the following research and achievements:（1）One-step electrospinning was used to prepare carboxylated silica/polyvinylidene fluoride nanofibers（SC/PVDF）with the raised structure.Inspired by the protein channel of proton transmission in organisms,polyglutamic acid（γ-PGA）was fixed on the surface of the SC/PVDF,and then impregnated with sulfonated polysulfone（SPS）to prepare the composite membranes（SPS/PGA@SC/PVDF）.The heterogeneous dual-interfaces composed of PVDF/SPS and SC/SPS in the membranes has a large number of hydrophilic groups（-COOH and-NH₂）to provide effective proton transport sites and form the long-range continuous proton transport channels in the composite membranes.The interaction of-COOH,-NH₂ and-SO₃H in SPS matrix could effectively reduce proton transition energy barrier and promote proton conduction in composite membranes.In addition,the three-dimensional network structure composed of fibers and the interaction between functional groups formed a tortuous methanol diffusion path,which could effectively reduce methanol permeability and improve the mechanical strength of the composite membranes.Thanks to the above advantages,SPS/PGA@SC/PVDF-15%exhibited the highest proton conductivity of 0.324 S·cm^-1 and the lowest methanol permeability of3.76×10^-7 cm²·s^-1,indicating excellent comprehensive performance.（2）Coaxial dual-component electrospinning was used to create carboxylated cellulose whisker/polyvinylidene fluoride nanofibers（CW/PVDF）with the villiform structure,which further expanded the interaction area between fiber and matrix.The nanofibers were functionalized withγ-PGA and impregnated into the SPS matrix to obtain SPS/PGA@CW/PVDF.The test results of the performance of composite membranes indicated that SPS/PGA@CW/PVDF-15%exhibited the highest proton conductivity(0.582 S·cm^-1)and power density(201.14 m W·cm^-2),as well as good water absorption capacity,dimensional stability,methanol permeability and mechanical strength,exhibiting excellent comprehensive performance.The first principle calculation based on the density functional theory（DFT）was used to further reveal the transfer process of protons between different interfaces of the composite membrane transport channels at a more microscopic level.It was found that the activation energy barrier between SO₃H（in SPS）and C=O and NH（inγ-PGA）was 0.130 and 0.663 e V,respectively,indicating thatγ-PGA played an important role in proton transmission.It was proved that PGA@CW/PVDF was a promising skeleton of proton transport highways in PEMs.