Electrospun polyacrylonitrile nanofiber mat protected membranes for vanadium flow batteries

Abstract

A cheap, efficient and durable proton exchange membrane is essential for vanadium flow batteries (VFB). The sulfonate poly(ether ether ketone) (SPEEK) membrane is a leading candidate to replace the widely used Nafion series membranes because of high proton to vanadium ion selectivity and low-cost. However, poor chemical/mechanical stability still hinders the practical application of the SPEEK membrane in VFB. Herein, we report a simple and robust strategy by using an electrospun polyacrylonitrile (PAN) nanofiber mat as a protection layer to improve the stability of the SPEEK membrane. The PAN nanofiber mat can prevent the damage to the SPEEK membrane from the vanadium electrolytes, graphite (carbon) felt electrodes and sealing gaskets, without affecting the VFB performance. Therefore, the PAN nanofiber mat–SPEEK–PAN nanofiber mat (P–S–P) sandwich membrane demonstrates excellent rate performance and superior cycling stability over 1000 charge/discharge cycles at a current density of 120 mA cm⁻².