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 polytetrafluoroethylene/Nafion/silica composite membrane was prepared.•The membrane was prepared by solution casting method with nano SiO2 powder.•The vanadium cell with the composite membrane exhibited good performance.•Membrane properties between the casting and sol–gel method were compared.

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.