Carbon black-coated SPEEK membrane for efficient vanadium flow batteries

Ion exchange membrane is a key component of vanadium flow batteries (VFB). Development of low-cost and high ion selectivity membrane is essential to promote practical application of VFB. Here we report a kind of carbon-coated membrane by spraying coating Super P/polyvinylidene fluoride slurries on the surface of sulfonated poly(ether ether ketone) membrane (SPEEK/SP@PVDF). The SP attached to the membrane surface or infiltrated into the membrane matrix can synergistically promote the transport of protons while inhibiting the penetration of vanadium ions. In addition, the surface SP@PVDF layer can effectively shield the strong oxidizing VO2+ in the posolyte. As a result, the VFB with the optimized SPEEK/SP@PVDF membrane demonstrates a stable energy efficiency of >80 % at 200 mA cm−2 and a peak power density of 1073.79 mW cm−2 at 1300 mA cm−2, indicating the great potential of this carbon black-coated membrane for potential application in VFB.