| Proton exchange membrane（PEM）,as the"heart"of methanol fuel cells,directly determines the power density of the fuel cell.How to improve the trade-off effect between proton conductivity and methanol permeability is still a key challenge that restricts the preparation of high-performance PEMs.To solve the abobe problem,the sulfonated polyethersulfone（SPES）nanofibers with different sulfonation degrees were optimized,MOFs nanofibers with hierarchical structures（Ui O-66-NH2@NFs hybrid nanofibers,SPES@ZIF-8 hybrid nanofibers,MIL-53（Al）-NH2 nanofibers）were synthesized via electrospinning technique.The mechanism of MOFs nanofibers in regulating the interface structure and proton conducting channel structure of composite proton exchange membrane were revealed.The high-performance composite PEM with simultaneously enhanced proton conductivity and methanol barrier are obtained.The research contents are as follows:（1）By adjusting the spinning solution concentration,spinning voltage,and receiving distance,the optimal spinning process of electrospinning SPES nanofibers was determined.The study on the water uptake,swelling rate,proton conduction,methanol permeability of SPES nanofiber/Nafion composite membranes under different sulfonation degree were emphasized and the optimal degree of sulfonation of SPES were determined.The results provide a basis for the construction of MOFs nanofiber composite proton exchange membranes with SPES in the later works.（2）Ui O-66-NH2 anchored SPES composite nanofibers（Ui O-66-NH2@NFs）with3D connected network structure were prepared by blending electrospinning technology.Due to the structural advantages and the acid-base interaction between the-SO3H and-NH2 groups,the interface compatibility between the fiber and the matrix were effectively enhanced when Ui O-66-NH2@NFs were introduced into the Nafion matrix,leading to a prevented methanol permeability of 7.54 cm2 s-1.At the same time,the proton conducting sites in the Ui O-66-NH2@NFs/Nafion composite membrane increased to 0.270 S cm-1（80°C,100%RH）.The maximum power density of the membrane in the single cell can reach to 95.490 m W cm-2.（3）Taking the electrospun SPES nanofibers as templates,the composite SPES nanofibers（ZSNFs）with ZIF-8 on the surface were constructed by adjusting the reaction time and the molar ratio of Zn2+to Hmim in the reaction solution.Due to the"bridging"effect of ZIF-8,the interfaces between the composite membranes are tightly bonded,further improving the barrier to methanol.The methanol permeability of the hybrid membranes was reduced to 3.03×10-7 cm2 s-1.In the meantime,the interfacial-SO3H…Hmim pairs provided abundant transfer sites,and the proton conductivity reached to 0.265 S cm-1（80°C,100%RH）.The maximum power density of ZSNFs/Nafion composite membrane is 116.50 m W cm-2.（4）The electro-blown spinning Al2O3 nanofibers were selected as metal source to react with the ligand（H2BDC-NH2）.By adjusting the reaction time,MIL-53（Al）-NH2nanofibers with an ultra-high specific surface area(1005.99 m2 g-1)were prepared without polymer template.The role of fibrous MOFs in composite membranes was further expanded.The hydrophilicity,long-range consecutive structure as well as the active proton carriers（-NH2 groups）of MNFs provided sufficient transfer sites and continuous transfer channels for proton conducting.The proton conductivity of MNFs@SPES composite membrane reached to 9.111×10-4 S cm-1（80°C,20%RH）,0.248 S cm-1（80°C,100%RH）.The interfacial acid-base pairs between the MNFs and the SPES matrix greatly improved the interfacial compatibility,resulting in a decrease in methanol permeability of 1.31×10-7 cm2 s-1.The maximum power density of the composite membrane reached to 92.063 m W cm-2,which provided new ideas for the preparation of low-cost,high-performance PEMs. |
