Effect of nafion membrane thickness on performance of vanadium redox flow battery

The performance of vanadium redox ow batteries (VRFBs) using different membrane thicknesses was evaluated and compared. The associated experiments were conducted with Nafion (R) 117 and 212 membranes that have 175 and 50 mu m of thickness, respectively. The charge efficiency (CE) and energy efficiency (EE) of VRFB using Nafion (R) 117 were higher than those of VRFB using Nafion (R) 212, while power efficiency was vice versa. In terms of amounts of charge and discharge that are measured in different charging current densities, the amounts in VRFB using Nafion (R) 212 are more than that in VRFB using Nafion (R) 117. To further characterize the effect of membrane thickness on VRFB performance, electrochemical impedance spectroscopy (EIS) and UV-vis. spectrophotometer (UV-vis) were used. In EIS measurements, VRFB using Nafion (R) 117 was more stable than that using Nafion (R) 212, while in UV-vis measurements, vanadium crossover rate of VRFB usingNafion (R) 212 (0.0125M/hr) was higher than that of VRFB using Nafion (R) 117 (0.0054 M/hr). These results are attributed to high crossover rate of vanadium ion in VRFB using Nafion (R) 212. With these results, vanadium crossover plays more dominant role than electrochemical reaction resistance in deciding performance of VRFB in condition of different membranes.