Design and synthesis of highly stable poly(tetrafluoroethylene)-zirconium phosphate (PTFE-ZrP) ion-exchange membrane for vanadium redox flow battery (VRFB)

Vanadium redox flow battery (VRFB) is a promising technology for large-scale renewable energy storage. Design of ion-exchange membrane (IEM) with desired properties like low-cost, mechanically chemically stable, low vanadium ion permeability and high proton conductivity is one of the major challenges. Here, we report the design and synthesis of novel poly(tetrafluoroethylene)-zirconium phosphate (PTFE-ZrP) asymmetric IEM using a simple brush coating method. XRD results confirmed the presence of α-ZrP crystalline phase onto the top layer of the membrane. Excellent mechanical strength was observed with burst pressure of 3.22 × 10⁵ N m^?2. Oxidative stability of membrane in Fenton’s reagent was much better than Nafion-115. Vanadium ion (V⁴⁺) permeability of the membrane was more than three times lower than that of Nafion-115. Single-cell VRFB with PTFE-ZrP membrane showed ～80% energy efficiency below 30 mA cm^?2. Very high columbic efficiency ～100% of VRFB with PTFE-ZrP membrane confirmed little contamination of electrolyte due to cross-mixing.