Highly Efficient and Low Cost SPEEK/TiO₂ Nanocomposite Membrane for Vanadium Redox Flow Battery

In this work, a sulfonated poly(ether ether ketone)/titanium oxide composite membrane (SPEEK/TiO₂) was prepared by solution casting method. The TiO₂ nanoparticles in the polymer matrix not only improved the vanadium ion selectivity of SPEEK/TiO₂, but also enhanced the mechanical stability of this membrane by forming hydrogen bonds with SPEEK. Based on the SPEEK/TiO₂ composite membrane, vanadium redox flow battery (VRB) exhibited ultrahigh coulombic efficiency (over 99.3%) and excellent energy efficiency (over 84.8%) under current density of 120 mA cm^-2 for 200 cycles. More importantly, the device also presented excellent discharge capacity retention performance of about 95.4% and 86.9% after 100 and 200 cycles under this current density, respectively. The good performance and low cost of this membrane indicate that it is a promising candidate in VRB applications and an excellent substitute for Nafion membranes.