Investigation on physico-chemical and electrochemical performance of poly(phenylene oxide)-based anion exchange membrane for vanadium redox flow battery systems

Abstract

Efficient and cost-effective membranes to increase sustainability of electrochemical energy conversion systems consisting of vanadium redox flow batteries (VRFBs) have received wide-range of attention. In this research, to investigate the feasibility of an anion exchange membrane for VRFBs, we fabricated a cost-effective poly(phenylene oxide)-based Im-bPPO membrane through facile preparation techniques. Physico-chemical and electrochemical measurements proved that the Im-bPPO membrane could be considered as a membrane candidate for VRFB applications. The Im-bPPO membrane exhibited good water uptake behavior and an ion exchange capacity of 0.71 meq/g. The anion exchange properties of the Im-bPPO membrane showed a reasonable proton conductivity of 12 mS/cm, which can facilitate proton transportation during unit cell operation. The presence of –OH functional group and water molecules in the membrane can induce proton transportation. Moreover, vanadium (V4+) ion crossover was significantly prohibited by the Im-bPPO membrane, which was considerably lower than the Nafion membrane. Vanadium permeability of the Im-bPPO membrane is 0.0678 × 10−7 cm2 min−1. A unique advantage of the Im-bPPO membrane is raising the Donnan exclusion effect during the unit cell operation, where the same charge of vanadium ion is repulsed by the Im-bPPO membrane. Furthermore, a reasonable VRFB unit cell performance was obtained by the Im-bPPO membrane. The coulombic efficiency of the Im-bPPO membrane (99.5%) is higher than that of the Nafion membrane (93%) under identical conditions during the 5th cycle, which can enhance the overall VRFB performance. This research work provides an insight into Im-bPPO-based anion exchange membranes for VRFB systems.