| As a kind of large-scale energy storage device,VRFB have been widely concerned in recent years.Proton exchange membrane,as its core component,have been the bottleneck of its development.At present,Nafion series membranes are still the most widely used,but its high cost and low resistance to vanadium limit the promotion and application of vanadium battery.Porous separation membrane is a very important type in existing vanadium battery membranes.Therefore,a series of porous membranes and nanocomposite porous membranes with different structures were designed and prepared by structural modification of polybenzimidazole?PBI?membranes,and their related properties were studied.The main content is as follows:1. Asymmetric porous membrane?PMV membrane?with single dense skin-layer was obtained by using proton solvent mesylate?MSA?and water vapor induced phase separation?VIPS?to control the membrane formation conditions.Compared with the aprotic solvent DMAc,VIPS and NIPS were used respectively to obtain honeycomb porous membrane?PDV membrane?without dense layer and the pipe-like porous membrane?PDN membrane?with double dense layers by adjusting the process.By characterizing the structures and properties of these three membranes,it is concluded that PMV membrane have the optimal ion selectivity and are suitable for the application of VRFB.Then,the influence of casting liquid concentration on the morphology and performance of PMV membrane was studied in detail,and the optimal casting liquid concentration of PMV membrane was 6 wt%?P6 membrane?,which showed the highest ion selectivity(7.207×105S·min·cm-3),about 8 times that of Nafion 115 membrane(9.314×104 S·min·cm-3).In addition,when the current density is in the range of 40 m A·cm-2-120 m A·cm-2,the energy efficiency of the P6membrane?91.44%-81.01%?is always higher than that of Nafion 115 membrane?88.19%-77.19%?,and at 160 m A·cm-2,the coulomb efficiency,voltage efficiency and energy efficiency remained stable after the P6 membrane was continuously run for more than 3000 times.2. The two-dimensional nanosheet structure of boehmite was introduced into the proton exchange membrane for the first time.Firstly,the two dimensional nanosheet material of boehmite?BNP?was prepared by hydrothermal method,and a honeycomb PBI porous membrane was prepared by NIPS method as the base membrane,Then“in situ growth”method was used to introduce the two-dimensional nanosheet structure into the surface of the PBI porous membrane,and a kind of laminated composite membrane PBI-BNP with nanometer lamellar structure was obtained.The proton conductivity of the porous membrane reached 187.16 ms·cm-1,nearly 50%higher than that of the PBI porous membrane(123.83 ms·cm-1),and 3.4 times higher than that of the Nafion membrane(55.49 ms·cm-1).Then,a PBI dense surface layer was introduced on the nanostructure surface of the PBI-BNP layered porous membrane by unwinding process to prepare the“sandwich”PBI-BNP-PBI composite membrane.The ion selectivity of the composite membrane reached 10.23×105 s·min·cm-3,nearly 10times higher than that of the porous PBI membrane(1.06×105 s·min·cm-3),and nearly20 times higher than that of the Nafion membrane(0.47×105 s·min·cm-3). |
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