Ultra-thin polytetrafluoroethene/Nafion/silica membranes prepared with nano SiO₂ and its comparison with sol-gel derived one for vanadium redox flow battery

Ultra-thin (~ 30 μm) polytetrafluoroethene (PTFE)/Nafion/silica composite membranes for all vanadium redox flow battery (VRB) are prepared via solution casting method. The membranes are prepared using nano SiO₂ powder with composition of 1% to 9%. Water uptake, proton conductivity, area resistance and vanadium ion permeability of the membrane are measured to evaluate the membrane properties. The membrane with 3% SiO₂ content (P/N/S-cast-3) shows the best cell performance among all the prepared composite membranes compared to that of the pristine PTFE/Nafion membrane. Furthermore, the properties of the P/N/S-cast-3 membrane are also compared to that of the membrane prepared by sol-gel method in literature. Experimental results indicate that the membranes prepared with nano SiO₂ powder show promising prospects for VRB application. However, its performances are not as good as the P/N/S composite membrane prepared by sol-gel method due to the aggregation of nano SiO₂ powder.