Preparation And Performance Of Sulfonated Polyether Ether Ketone-based Composite Membranes For All-vanadium Redox Flow Batteries

As a promising large-scale energy storage system,vanadium redox flow battery(VRFB)can be combined with renewable energy to provide stable and low-pollution energy for production through reversible transformation between electrical energy and chemical energy.As a key component,proton exchange membrane(PEM)is not only a physical barrier to separate positive and negative electrolytes,but also to ensure reversible transport of protons in the membrane.The Nafion membranes have excellent chemical stability and proton conductivity,but the higher cost and vanadium ion permeability limit further development.Therefore,it is a hot issue to study the low-cost,high-ion-selective proton exchange membrane,and the trade-off effect between the cost and efficiency is also an important issue.Sulfonated poly(ether ether ketone)(SPEEK)has some advantages such as mature preparation method,easy availability of raw materials and excellent physicochemical properties.However,the ion selectivity of SPEEK membrane is related to the degree of sulfonation,and it is necessary to optimize the balance between proton conductivity and vanadium ion permeability.In this paper,a series of composite membranes are prepared by doping nano-fillers with different structures in SPEEK matrix.And the modification methods of PEM are explored which improve the ion selecticity and optimize the balance of proton conductivity and vanadium ion permeability.The SPEEK/Lap composite membranes are prepared by doping laponite(Lap)in SPEEK matrix.The effects of multi-layer structure and-OH groups on the physicochemical properties of the composite membrane are investigated.In addition,the performance of the SPEEK/Lap-0.2 membrane and the SPEEK/GO-1 membrane are compared.The results show the nanofillers which have monolayer and high aspect ratio are beneficial to reduce the vanadium ion permeability of the composite membrane.However,these unmodified nanofillers have a poor influence on the balance of vanadium ion permeability and proton conductivity of the PEM.Therefore,the GO nanosheets were modified with 4,4-diamino-2,2-biphenyldisulfonic acid(BDSA).The SPEEK/GO-BDSA composite membranes are prepared by doping GO-BDSA in SPEEK matrix.The results show that the SPEEK/GO-BDSA-1 membrane has the highest ion selectivity and proton conductivity.In the single cell test,the SPEEK/GO-BDSA-1 membrane also exhibited excellent structural stability,cycle stability and battery efficiency,and illustrate that the interaction from GO-BDSA nanosheets and SPEEK matrix contributes a major role.SPEEK/ GO-BDSA hybrid membrane shows a promising proton exchange membrane application for VRFB system.