Novel amphoteric ion exchange membranes by blending sulfonated poly(ether ether ketone)/quaternized poly(ether imide) for vanadium redox flow battery applications

For vanadium redox flow battery (VRB) applications, novel amphoteric ion exchange membranes (AIEMs) are prepared using sulfonated poly(ether ether ketone) (SPEEK) and quaternized poly(ether imide) (QAPEI) by a facile method. Different from other AIEMs synthesized by multiple steps, SPEEK/QAPEI (S/Q) membranes are directly prepared by blending. It offers a reduction in cost and leads to a high degree of micro-phase separated structure which could facilitate ion transport. The mechanical properties, thermal stability and oxidative stability of S/Q blend membranes are examined. In addition, increasing the content of QAPEI in the blend membranes could reduce water uptake and vanadium ion permeability effectively and improve the proton selectivity. In VRB single cell tests, the VRBs with S/Q blend membranes show higher coulombic efficiency and energy efficiency (EE) than pristine SPEEK and Nafion 115 membranes. Furthermore, the blend membranes present stable performance up to 100 cycles without significant decline in EE. All experimental results indicate that the S/Q blend membranes show promising prospects for VRB applications.