Amine functionalized graphene oxide containing C16 chain grafted with poly(ether sulfone) by DABCO coupling: Anion exchange membrane for vanadium redox flow battery

Abstract

Under strong oxidative environment of vanadium redox flow batteries (VRFB), membrane instability is a serious challenge. Anion exchange membranes (AEMs) are expected to reduce vanadium ion permeability due to Donnan exclusion. Herein, we report long alkyl chain grafted quaternized graphene oxide bonded poly(ether sulfone) by 1,4-diazabicyclo[2,2,2]octane (DABCO) coupling, which provides plenty of amine groups. This helps to improve the ionic conductivity. Whereas, long alkyl chain (C16) grafted quaternized graphene oxide causes well phase separation (hydrophilic-hydrophobic) and decent ionic pathway for ionic transportation. The reported AEMs showed good stabilities under harassed acidic/oxidative conditions due to the bulky nature of chemically grafted QG with the main polymer backbone. This results steric hindrance to resist the attack of oxidative species. Suitably optimized PS-DTQG-5 AEM, showed 32.46% water uptake, 2.14 meq/g ion exchange capacity, 6.06 × 10−2 S/cm ionic conductivity, and 18.93 × 105 S min cm−3 selectivity for VRFB. The VRFB assembled with PS-DTQG-5 AEM, displayed extremely good efficiencies (coulombic (98.06%), energy (76.4%), and voltage (78.0%)) at 60 mA cm−2, higher than those for Nafion 117 membrane. Further, stabilities under ex-situ oxidation conditions and in-situ cycle test (approx. 80) in VRFB operating environment make PS-DTQG-5 AEM as an attractive candidate.