Investigation on various types of ion-exchange membranes in vanadium redox flow batteries: Experiment and modeling

Choosing the appropriate ion exchange membrane in vanadium redox flow batteries plays an important role in achieving optimal system performance. In this article, the implementation of commercial cation exchange membranes (Nafion 115, Nafion 117, and Nafion 212), anion exchange membranes (FAP 450 and QA-PFE), and the combination of them are investigated. In this regard, the effects of membrane type, thickness, electrical conductivity, and the transfer of vanadium species at different current densities are examined carefully. In addition, the influences of the flow rate and the concentration of electrolytes are investigated using a comprehensive developed model. The model predictions are validated against the experimental data of a charge and discharge cycle of cation and anion exchange membranes with a mean relative error of 2.06 %. It is found that FAP 450, despite the relatively low thickness, provides the highest capacity retention (91.19 %) after twenty working cycles. This can be attributed to the anion exchange nature and having the lowest diffusion coefficients of vanadium species. In addition, Nafion 212 provides the highest power density (256 mW cm(-2)) among the examined membranes. It can be attributed to the inverse relation between system power density and membrane ohmic resistance. Moreover, charging and discharging time, efficiency, maximum power density, and capacity fade of the system are functions of net transfer rate of vanadium species, thickness, and electrical conductivity of the membrane combination. Furthermore, the maximum and minimum values of the peak power densities of the system are 244 and 210 mW cm(-2), which are obtained for the combination of Nafion 212-Nafion 212 and Nafion 117-Nafion 117, respectively. Finally, the maximum and minimum values of the capacity retention of the system after twenty working cycles are 93.39 % and 75.25 % for combinations of FAP 450-FAP 450 and Nafion 212Nafion 212, respectively.