A non-ionic membrane with high performance for alkaline zinc-iron flow battery

Alkaline zinc-iron flow battery (AZIFB) is emerged as one of the cost-effective technologies for electrochemical energy storage application. A cost-effective ion-conducting membrane with high performance is very important for the battery. In this paper, a cost-effective non-ionic poly (ether sulfone) (PES) membrane with high ion conductivity and high anti-alkali stability is designed for AZIFB. The non-ionic membrane is constructed by using PES as the matrix, while a bifunctional polyethylene glycol (PEG) is employed as additive. The PEG can on the one hand conduct charge-balancing ions through the alkalized-ether functionality, while on the other hand, create nano-scale pores in the matrix by partially dissolving in water. Thus, the battery with an optimized membrane exhibits a coulombic efficiency (CE) as high as 99.26% and an energy efficiency (EE) of 86.81% at a current density of 80 mA cm-2. Moreover, after soaking the non-ionic membrane in 6 mol L-1 NaOH at 50 °C for 8 days, the battery operating at 80 mA cm-2 can still steadily run for 120 cycles, demonstrating high anti-alkali stability. The above results suggest that the non-ionic membranes present very promising prospects for AZIFB.