| All-vanadium redox flow battery（VRFB）has attracted much attention as a large-scale energy storage system.In VRFB system,ion exchange membrane is a key component which directly affects the performance.At present,there are still some defects in the ion exchange membrane used in VRFB,such as the difficult balance of ionic conductivity and selectivity,excessive water absorption and swelling under high functionalization,and lack of chemical stability,etc.The amphoteric ion-exchange membrane is a kind of membrane which contains both cation exchange group and anion exchange group,which can exhibits high conductivity and selectivity at the same time,and has a broad prospect of research.In this thesis,three kinds of amphiphilic membranes with new structures were designed and prepared by means of blending,grafting and cross-linking.And the structure and performance of the membranes were tested and studied in an all-round way.Firstly,A novel amphoteric membrane was designed by blending triple tertiary amine grafted poly（2,6-dimethyl-1,4-phenylene oxide）（PPO-TTA）with sulfonated poly（ether ether ketone）（SPEEK）.The protonation of tertiary amine groups and the acid-base coupling effect with sulfonic acid can not only promote the construction of efficient hydrogen bond networks in the membranes and improve the proton conduction capacity of the membranes.But also effectively inhibited the water swelling and vanadium permeation of the membrane and protected the main chain of the polymer.The SPEEK/PPO-TTA-15%membrane simultaneously showed a low vanadium permeability(3.4×10-99 cm2 s-1)and surface resistance（0.39Ωcm2）.The EE of the membrane is 88.6%at 80 mA cm-2,and 77.1%at 200 mA cm-2,and its performance does not decrease significantly after 200 cycles,which showing excellent VRFB application prospect.Then,in order to solve the difficulty of improving IEC and the need for further improvement of stability in the blend amphoteric membrane,a poly（arylene piperidinium）（PBPip）polymer without any aryl ether bond in skeleton was synthesized by condensation of biphenyl and N-methyl-4-piperidine under the catalysis of superacid.And a novel amphoteric side-chain functionalized ion exchange membrane was designed and fabricated based on this polymer in this work.The unique amphiphilic side chain structure enables the content of both positive and negative groups in the membrane to be increased at the same time,thus it has excellent ionic conduction capacity.And the polymer skeleton without aryl ether bond makes it have good chemical stability.The total value of IEC of AMPBPip-70 membrane can reach 4.19mmol g-1,and the area resistance are only 0.22?cm2.After 30 days of oxidation,the mass loss is only 4.5%and it’s FTIR spectrum has no obvious change.It shows excellent VRFB performance at high current density,the EE can reach more than 80%at 200 mA cm-2,and there is no significant decrease in CE,VE and EE after 500 cycles.However,the vanadium permeability of this membrane is relatively high(1.31×10-88 cm2 s-1),which affects the VRFB performance of the membranes at low current density(86.3%of EE at 80 mA cm-2).Based on the previous study,a novel amphoteric side-chain functionalized crosslinked ion exchange membrane was designed and prepared by cross-linking reaction.Through the cross-linking network structure,the content of positive groups in the membrane was further increased and the distance between the molecular segments was shortened,which reduces the size of the hydrophilic ion channel in the membrane.Without seriously reducing the ionic conductivity,the vanadium permeation of the membrane were inhibited effectively,and the CE of the membrane was further enhanced.The IEC of Cr-AMPBPip-70-30 membrane is as high as 4.93 mmol g-1,and the surface resistance and vanadium permeation are only 30?cm2 and0.79×10-88 cm2 s-1,respectively.It shows 88.7%of EE at 80 mA cm-2 current density and still can up to 78.2%of EE at 200 mA cm-2,achieving more balanced and superior VRFB performance. |
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