Nafion/polyvinylidene fluoride blend membranes with improved ion selectivity for vanadium redox flow battery application

► Ion exchange membranes based on Nafion/PVDF blends were prepared and first investigated in VRB application. ► The addition of PVDF would confine the swelling and improve the ion selectivity. ► In VRB single cell test, the blend membranes exhibited superior performances compared with pure recast Nafion. ► The blend membranes have great potential for practical application, due to their preparation method is facile, highly reproducible and less Nafion consumed. Nafion/PVDF blends are employed to prepare the ion exchange membranes for vanadium redox flow battery (VRB) application for the first time. The addition of the highly crystalline and hydrophobic PVDF effectively confines the swelling behavior of Nafion. In VRB single cell test, the Nafion/PVDF binary membranes exhibit higher columbic efficiency than recast Nafion at various current densities. The blend membrane with 20 wt% of PVDF (N 0.8P 0.2) shows energy efficiency of 85% at 80 mA cm −2, which is superior to that of recast Nafion. N 0.8P 0.2 membrane also possesses twice longer duration in OCV decay test and much lower permeation of VO 2+ compared with recast Nafion. These results indicate that the addition of PVDF is a simple and efficient way to improve the ion selectivity of Nafion, and the polymer blends with optimized mass fraction of PVDF show good potential for VRB application.