Preparation And Properties Study Of Nafion^? Composite Membranes For Use In VRB

The vanadium redox flow battery(VRB) has the advantages of good electrochemical properties, cost-efficiency, easy scale-up, and safety, which make it suitable for large scale energy storage. The proton exchange membrane is one of the key materials in a VRB and currently Nafion~? is widely used due to high chemical and mechanical stability and its excellent electrochemical properties. However it has the drawback of high cost and high vanadium permeation and the latter leads to performance degradation. Consequently, developing a cost-efficient membrane with high proton conductivity and low vanadium ion permeability is a research hotspot in the further development of VRBs.In this research, two types of MFI zeolites: Silicalite-1 and ZSM-5, have been synthesized and used as fillers in Nafion~?(D520) to form a composite membrane for use in a VRB. The MFI type zeolites were synthesized with 100% Si(Silicalite-1) and Si/Al =22(ZSM-5), Si/Al = 11(ZSM-5) and used at 2.5 wt%, 5.0 wt%, 7.5 wt%, 10 wt% loading in Nafion~?. A range of properties have been measured such as: IEC, water uptake, vanadium ion permeability, proton conductivity, and cell charge-discharge efficiency using a range of current densities(40, 80, 120, 160, and 200 mA/cm2) in order to evaluate the composite MFI/Nafion~? membrane and in particular the capacity decay.The results obtained show that the composite MFI/Nafion~? membrane can give an enhanced performance in comparison to the blank Nafion~? membrane and the different zeolites have different influence on the properties. The use of MFI zeolites are expected to act as a physical barrier to vanadium cross over and the ZSM-5 will also have internal Br?nsted acid sites and these are known to contribute to proton conduction. Comparison between the results obtained show the ZSM-5 zeolite with 5 wt% loading in Nafion~? is more efficient than the other MFI loadings and the capacity decay is lowest when ZSM-5 is used as the filler. In conclusion the results presented here add to the knowledge base for the development of suitable membranes for lowering the capacity decay that occurs in VRBs.