Sulfonated poly(ether ether ketone)/polyimide acid-base hybrid membranes for vanadium redox flow battery applications

Abstract

A series of acid-base hybrid membranes based on sulfonated poly(ether ether ketone) (SPEEK) and polyimide (PI) were prepared and used for vanadium redox flow battery (VRFB). The proton conductivity, vanadium ion permeability, ion-exchange capacity (IEC), and water uptake of the SPEEK/PI (S/PI) hybrid membranes were tested. It was observed that the S/PI hybrid membrane exhibited lower vanadium ion permeability and higher selectivity than SPEEK and Nafion115 membranes. The VRFB single cell with S/PI hybrid membranes exhibited a better overall performance, such as higher coulombic efficiency (CE) of 96%, higher energy efficiency (EE) of 84%, and longer discharge time (DT) of 41 h, than that with the Nafion115 membrane (CE 92%, EE 82%, and DT 27 h) at 60 mA cm−2. The results showed that the S/PI acid-base hybrid membrane is a potential candidate for VRFB.