Preparation And Properties Of Sulfonated Polyetheretherketone Composite Membranes For All-vanadium Redox Flow Batteries

In order to acquire secure and large-scale energy storage system for the utilization of renewable energy,vanadium redox flow battery（VRFB）has been widely investigated owing to its remarkable characteristics such as high efficiency,fast response,long cycle-life,modular design and the storage and release of electrical energy are realized.As the key material of VRFB system,the proton exchange membrane（PEM）plays the role of isolating the positive and negative electrolytes and provides the necessary proton transmission channels.Simultaneously,an exellent PEM should have the characteristics of high proton conductivity,low vanadium ion permeability,excellent physical and chemical stability and low cost.Therefore,it is significant important to research on PEMs with excellent comprehensive performance and low cost of vanadium redox flow batteries.Sulfonated poly（ether ether ketone）（SPEEK）has been widely used due to its excellent physical and chemical properties and low cost.However,its degree of sulfonation is closely related to the ion selectivity of the membrane.Therefore,It is an important way to increase the ion selectivity and physical and chemical properties of the SPEEK membrane by adding second component.In this paper,a series of composite proton exchange membranes were prepared by adding different sulfonic acid functionalized organic and inorganic nanofillers to SPEEK matrix,and further explore a modification method to improve the physicochemical properties and ion selectivity of PEM.Polyphenylene sulfide（PPS）has excellent physical and chemical properties as a new high-performance organic polymer material.Meanwhile,in this paper,sulfonated polyphenylene sulfide（SPPS）was successfully prepared using chlorosulfonic acid to functionally modify polyphenylene sulfide,and a series of SPEEK/SPPS organic-organic composite proton exchange membranes were prepared by blending with SPEEK matrix.The results show that the SPEEK/SPPS-15 composite membrane has excellent physical and chemical properties,ion selectivity and proton conductivity.In addition,the SPEEK/SPPS-15 composite membrane showed the highest battery efficiency,excellent cycle stability and structural stability in the self-assembled single cell test,and which proved that the addition of sulfonated SPPS organic particles can not only change the internal structure of the membrane,and it has a positive impact on the overall performance of the composite proton exchange membrane.The SPEEK/S-TiO₂organic-inorganic composite proton exchange membranes are prepared by doping S-TiO₂ in SPEEK matrix.The sulfonic acid-functionalized titanium dioxide（S-TiO₂）was prepared by the post-sulfonation method using titanium dioxide（TiO₂）as the raw material.The effects of S-TiO₂ structure and functional group on the physicochemical properties of the composite membrane are investigated.Obviously,the result show that the SPEEK/S-TiO₂-3 composite membrane has the highest proton conductivity and ion selectivity,and the lowest vanadium ion permeability,and the physical and chemical properties of SPEEK/S-TiO₂-3 composite membrane is significantly improved by comparing with SPEEK membrane.In the single cell test,the SPEEK/S-TiO₂-3 composite membrane also exhibited excellent battery efficiency and cycle stability.