Poly(p-phenylene)-based membrane materials with excellent cell efficiencies and durability for use in vanadium redox flow batteries

Poly(p-phenylene)-based ionomers with remarkable durability and rate capability for use in vanadium redox flow batteries (VRFBs) are reported. The family of synthesized ionomers, sPBPSP-z, exhibited not only well-developed phase separation between hydrophilic domains and hydrophobic domains but also well-connected hydrophilic channels, resulting in enhanced proton conductivities and excellent dimensional stabilities. sPBPSP-8, which has an ion exchange capacity of 1.83 meq g-1, showed high discharge capacity retention and superior efficiencies over 100 cycles at a current density of 50 mA cm-2. In addition, the sPBPSP-8 ionomer exhibited stable performance at various current densities (50-180 mA cm-2) and retained high efficiencies at high current densities. Furthermore, this material exhibited superior chemical stability under oxidizing conditions, excellent capacity retention, and high efficiencies during long-term VRFB operation (1000 cycles). These results indicate that the sPBPSP-8 membrane is a superb material for VRFB applications.