Sulfonated poly (ether ketone)/sulfonated titanium dioxide hybrid membrane with high selectivity and good stability for vanadium redox flow battery

A series of sulfonated poly (ether ketone)-based hybrid membranes are fabricated with sulfonated titanium dioxide (S-TiO2) as the performance modifiers via the solution-casting method. Under various contents of S-TiO2 nanofillers, the SPEEK/S-TiO2 hybrid membranes display superior ion selectivity and vanadium ion resistance to Nafion 117 and SPEEK membrane, and the SPEEK/S-TiO2–3 demonstrates an excellent ion selectivity (33.1 × 103 S min cm−3) and vanadium ion resistance (7 × 10−7 cm−2 min−1). The cell assembled with the SPEEK/S-TiO2–3 membrane gives higher coulombic efficiency (98.2%) and energy efficiency (80.2%) than that of Nafion 117 (97.10% and 74.7%) at 100 mA cm−2 current density, and after 200-time charge-discharge cycles, the SPEEK/S-TiO2–3 membrane keeps good structural stability and durability, which is originated from the intramolecular interaction between the S-TiO2 nanofillers and the SPEEK matrix. Thus, the present study provides a promising method to develop low-cost hydrocarbon membranes with functional nanofillers through regulating molecular interaction.