A high performance polytetrafluoroethene/Nafion composite membrane for vanadium redox flow battery application

To reduce the consumption and improve the performance of Nafion, a thin polytetrafluoroethene (PTFE)/Nafion (P/N) composite membrane for vanadium redox flow battery (VRB) application was prepared by impregnating porous PTFE membrane with Nafion solution. The P/N membrane is almost as transparent as commercial Nafion 212 (N212) membrane, which can be easily cut into any desired shape and size. SEM and AFM analyses prove that the Nafion resin uniformly filled into the micro-pores of porous PTFE membrane. Results also show that the swelling ratio, Nafion consumption, water transport and vanadium ions permeability of P/N membrane are smaller than that of N212. The VRB with P/N membrane has higher coulombic efficiency, voltage efficiency and energy efficiency than that of N212 at all tested current densities, and the average EE of VRB with P/N membrane is 5.2% higher than that of the VRB with N212 at current densities from 40 to 70 mA cm^-2. Furthermore, owing to the lower vanadium ions permeability, the self-discharge of the VRB with P/N membrane is much slower than that of the VRB with N212, and 45 cycles charge-discharge test proves that the P/N membrane is very stable and has better capacity retention ability than that of N212.