Recent development and prospect of membranes for alkaline zinc-iron flow battery

Alkaline zinc-iron flow battery (AZIFB) is promising for stationary energy storage to achieve the extensive application of renewable energies due to its features of high safety, high power density and low cost. However, the major bottlenecks such as the occurrence of short circuit, water migration and low efficiency have limited its further applications, of which an ion-conducting membrane acts as a pivotal role in addressing these issues. The benchmark Nafion series membranes or anion-exchange membranes are confronted with their low ionic conductivity or poor stability in alkaline media. Therefore, a membrane is required to possess (1) excellent stability to avert the occurrence of short circuit resulted from the destruction of zinc dendrite and degradation of membrane caused by alkaline media, (2) low area resistance and high selectivity to achieve a high efficiency in time of the charge-discharge procedure of AZIFB. In this review, we will start from a brief introduction of AZIFB and cover the categories of membranes applied in AZIFB. And then the fundamental aspects of the membrane, including ion transport mechanism, fabrication & structure design and performance optimization will be highlighted. Finally, the challenges and prospects of the membranes for AZIFB applications will be briefly proposed and discussed.