Preparation And Properties Study Of SPEEK/Zeolite Composite Proton Exchange Membranes For Use In Vanadium Redox Battery

The vanadium redox flow battery is one of the most promsing systems for large scale renewable energy storage and has aroused much attention. Proton conducting membranes are the critical material in a VRB and the perfluorinated sulfonic acid membrane(PFSA) such as Nafion?, presently used, has high cost and low proton conductivity at higher temperature, especially it has poor ion selectivity and so it is necessary to develop alternative me mbranes. The sulfonated poly ether ether ketone(SPEEK) is a candidate, which outweighs PFSAs in cost, however the proton conductivity, mechan ical strength, and water adsorption need to be improved in SPEEK. Filers are a method to improve performance of SPEEK and zeolites are porous with high specific surface area, strong water adsorption, good ion exchange capacity, and so are a good choice as an inorganic filler.This work presented here uses three kinds of zeolites, namely LTA, NH4-A and H-A zeolities. LTA zeolite which were synthesized by hydrothermal and converted to NH4-A zeolite with NH4 Cl. H-A zeolite was converted by heating NH4-A zeolite in a water vapor atmosphere. Smaller grain sizes of three types of zeolites were prepared by ball milling.The SPEEK membranes were prepared by post-sulfonation method of PEEK under different sulfonation time(30 min~90 min). The SPEEK membranes, using a 70 min sulfonation time(SPEEK-70), had good performance e.g water uptake, ion exchange capacity(IEC), lower vanadium permeability, and higher proton conductivity.The SPEEK/zeolite composite membranes with the loading 2.5%, 5%, 7.5% and 10% were formed by recast method. Various characterization methods, which include: scanning electron microscope(SEM), Fourier t ransform infrared spectra(FT-IR), thermal gravimetric analysis(TGA) coupled with differential scanning calorimetry(DSC), ion exchange capacity(IEC), water uptake, vanadium permeability, proton conductivity, VRB cell performance, chemical stability and mechanical properties were used to characterize the prepared SPEEK and SPEEK/zeolite composite membranes. The results show that the 2.5% LTA/SPEEK-70 exhibited higher tensile strength than the SPEEK-70 membrane(11.69 MPa vs 4.56 MPa) but a lower coulombic and energy efficiency was obtained, at 80 m A·cm-2, compared with SPEEK-70 membrane(94.47% vs 94.78% and 83.04% vs 83.40% respectively).