Preparation Of Six-membered Ring Sulfonated Polyimide Ion Exchange Membrane For Vanadium Redox Flow

As one of novel energe storage device,vanadium redox flow battery?VRFB?achieved great attention with the constant development of new energe.The outstanding ion exchange membrane?IEM?is the key comnents of VRFBs.Nowadays,Nafion series membranes from Du Pont are widely used,but they are also nagged by their high price and low vanadium ion resistance.Polymide is favored due to its low cost,many species and ability to regulate the structure and property by changing the reagent.Sulfonated polyimide?SPI?is easily prepared,while its vanadium ion resistance should be improved to be IEMs.In this paper,a series of excellent SPI membranes are prepared and applied in VRFBs.The main contents are as follows:1? To improve the vanadium ion resistance of SPI membrane,in this paper,a fluorinated SPI?SPI-HFBAPP?was synthesized using 1,4,5,8-naphthalenetetracarboxylic dianhydride?NTDA?,2,2'-benzidinedisulfonic acid?BDSA?and 2-bis [4-?4-aminophenoxy?phenyl] hexafluropropane?HFBAPP?by high temperature one-step polymerization method for ion exchange membrane applications in vanadium redox flow battery?VRFB?.The fluorocarbon groups in SPI-HFBAPP lead to the reduction of water uptake.The vanadium ion permeation of SPI-HFBAPP membranes is 0.97×10-7·cm2·min-1,much lower than Nafion115?9.69×10-7·cm2·min-1?.At the current density of 100 m A·cm2,the coulombic efficiency?CE?,voltage efficiency?VE?and energy efficiency?EE?of the single cell with the SPI-HFBAPP membranes is 99.61%,84.89% and 84.56%,respectively.The EE is much higher than the value with N115?80.2%?because of its highest proton selectivity.The self-discharge time could last for 300 h,about thirteen times of the time with N115?22h??The fluorinated SPI membrane showed a stable battery efficiency during the 500 cycles.2? The metal-organic framework got great attention due to its varied structure.To improve the anadium ion resistance of SPI membrane,the Zr-based metal-organic framework?UIO-66-NH₂?was synthesized as additive to prepare a series of hybid membranes.The micropore size of UIO-66-NH₂ is between the Stokes radius of hydrated proton and hydrated vanadium ion,which might result in the enhance of vanadium ion resistance.The experimental data indicate that the vanadium ion resistance of hybid membranes was improved wth increasing UIO-66-NH₂ content.Meanwhile,it leaded to the increase of area resistance and the reduction of proton conductivity.The performance of hybid membrane?UIO-66-NH₂,1wt%?was better.At the current density of 120 m A·cm2,the EE of the single cell is 85.42%,higher than N115?79.58%?.The self-discharge time is 57 h.3? The graphite oxide was amine-functionalized to prepare GO-NH₂.It participated in the reaction as a kind of monomer.Three kinds of polyimide?SPI-GO?were synthesized with different molecular mass.The oxidative stability of SPI-GO membranes with higher molecular mass is better.As the result of introduction of GO-NH₂,the vanadium ion resistance and proton conductivity are improved?The vanadium ion permeation of SPI-GO-2 membrane is 0.91×10-7·cm2·min-1,and its proton selectivity?33.51 × 104 s min cm-3?is much higher than N115membranes?6.33×104s min cm-3?.At the current density of 100 m A·cm2,the single cell with the SPI-GO-2 membranes behaved best,its EE?87.49%?is better than N115?80.22%?.The membrane showed a stable battery efficiency during the 200 cycles.