Imidazole and imidazolium functionalized poly(vinyl chloride) blended polymer membranes reinforced by PTFE for vanadium redox flow batteries

A novel blended polymer membrane is prepared by a facile route for using as the diaphragm in vanadium redox flow batteries (VRFBs). The polymers polyvinylchloride (PVC) and polyvinylpyrrolidone (PVP) are first blended in a 1.2:1 mol ratio to give a PVP-PVC mixture, and the PVC in the mixture is then functionalized with 1-(3-aminopropyl)-imidazole (APIm). The functionalized polymers are impregnated into the porous polytetrafluoroethylene (PTFE) to fabricate membranes. The obtained membranes possess superior affinity to sulfuric acid mainly due to acid-base interactions between APIm groups and sulfuric acid molecules. The presence of hydrophobic PTFE restricts the deterioration of mechanical strength of membranes by doped acids. Moreover, the prepared membranes exhibit high oxidation stability and low vanadium permeability. The VRFB assembled with the proposed diaphragm displays energy efficiency above 82 % at a current density range of 20 to 120 mA cm⁻². The membrane-based VRFB demonstrates stable performance after over 50 charge–discharge cycles.