Preparation And Properties Of Amphoteric Ion Blend Membranes Based On Perfluoresulfonic Acid Resin (PFSA)

All-vanadium flow battery（VRB）,as a large-scale energy storage system,has attracted wide attention.As the key material of VRB,ion exchange membrane can prevent the cross mixing of positive and negative electrolyte on the one hand,and play the role of ion transport on the other hand.The ideal ion exchange membrane should have good ion conductivity,excellent vanadium resistance（ion selectivity）and chemical stability.Therefore,we blended perfluorosulfonic acid resin（PFSA）and quaternary amine salt ionic compounds,modified perfluorosulfonic acid resin,prepared amphoteric ion blending membrane,and collaboratively improved ionic conductivity and vanadium ion permeability.Specific research contents are as follows:First of all,the PFSA containing side chain sulfonic acid groups was mixed with small molecules of double-cationic D5D,the PFSA polymer chain side group sulfonic acid anion and D5D double cationic acid interaction,forming an ion crosslinking network,improving the tensile strength（25.1 MPa）and dimensional stability（swelling rate only 6.1%）of the membrane.When vanadium ion permeability was reduced(5.19×10^-7 cm²/min),all parameters were better than PFSA recast membrane performance,indicating that the preparation of blending membrane by supramolecular crosslinking method with non-covalent interaction of cation and cation can effectively improve the comprehensive performance of the membrane.In order to adjust the component compatibility between small molecule D5D and large molecule PFSA and optimize the two-component structure difference of the blend membrane,polycationic PDABCO was synthesized,and a series of PDABCO-PFSA blends with different component proportions were prepared.Supramolecular crosslinking between polymer chains endowed the membrane with good mechanical properties and stability.Greater reduction of vanadium ion penetration.The ionic conductivity of PDABCO-PFSA-2.5%was 91 m S/cm higher than that of Recast PFSA（53 m S/cm）.The vanadium ion permeability of PDABCO-PFSA-7.5%is similar to that of commercial Nafion 212.Moreover,in the all-vanadium flow battery test,PDABCO-PFSA-7.5%membrane showed good coulomb efficiency,and CE reached 88.43%at the current density of 160 m A/cm².The polycationic component structure in the blend membrane was further optimized,and the polypiperazine structure with more flexible main chain and good film forming property was used for reference,so as to have better compatibility with PFSA.The quaternary amination piperazine polymer PPIP was designed and synthesized to blend with PFSA,regulate the content of PPIP components in the blending membrane,induce the separation and assembly structure of microphase in the membrane,and effectively improve the membrane ion conductivity（306 m S/cm）.Quaternized polypiperazine cations interact with sulfonic acid anions of PFSA to form supramolecular cross-linked network structure,which effectively improves the stability of the membrane and the compactability of the internal structure of the membrane.Polypiperazine cations cooperate with vanadium ion Donnan effect,and no obvious vanadium ion permeation phenomenon is detected in the membrane over 450 hours.Among them,PPIP-PFSA-5%shows excellent ion selectivity,which is 168 times higher than Nafion212 membrane,has higher energy efficiency EE（about 80%）,and CE reaches more than 93%at the current density of 160 m A/cm².The comprehensive performance evaluation of PPIP-PFSA series films is better than that of commercial Nafion 212 membrane of the same specification,which has good commercial application value.