Styrene- co -DVB grafted PVDF proton exchange membranes for vanadium redox flow battery applications

Styrene–DVB copolymer grafted semi-interpenetrating type PVDF-based proton exchange membranes (PEMs) have been designed for vanadium redox flow battery (VRFB) applications. The PEM contains separate regions for the proton conduction via hydrophilic channels, whereas mechanical stability is maintained by the hydrophobic part present in the membrane matrix. Mechanical, thermal, and oxidative stabilities of the membranes are investigated. The VRFB test was conducted at 50 mA cm−2 and 100 mA cm−2 current densities. The HA-45 membrane displays better performance than the HA-35 membrane. The HA-45 membrane exhibits an excellent peak current density of 470 mA cm−2 and a power density of 336 mW cm−2. With the HA-45 membrane, a specific capacity of 20.30 and 21.11 A h L−1 was realized at 100 mA cm−2, and 50 mA cm−2, respectively, and they are comparable to the theoretical capacity of 26.8 A h L−1. This was possible due to the reduced crossover of vanadium ions through the membrane. The energy efficiency for the HA-45 membrane is 80% which is equivalent to that using Nafion 117 at 100 mA cm−2 current density. From these results, HA-45 is found to be a suitable membrane for VRFB applications.