Tertiary amino-modified GO/Nafion composite membrane with enhanced ion selectivity for vanadium redox flow batteries

Tertiary amino-modified graphene oxide (GO) nanosheet (named as TAGO) was successfully synthesized by gamma-ray radiation-induced grafting of dimethylaminoethyl methacrylate onto the surface of GO. Then, a novel Nafion-TAGO composite membrane was prepared by solution casting method and TAGO could be dispersed uniformly in the Nafion due to a good compatibility with the Nafion matrix. In the composite membrane, acid-base pairs were formed through hydrogen-bond network among the tertiary amino groups, the carboxylic acid groups and hydroxyl groups in TAGO and/or sulfonic acid groups in Nafion, respectively. Owing to the acid-base pair interactions (such as –SO3H … -N(CH3)2), the ionic channels for proton transport could be provided in the composite membrane. As a result, the Nafion-TAGO composite membrane exhibited excellent thermal stability, high proton conductivity, low VO2+ permeability and high ion selectivity. Therefore, the TAGO is a good candidate for the performance improvement of Nafion used in vanadium redox flow battery.