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(0.8)P(0.2)) shows energy efficiency of 85% at 80 mA cm(-2), which is superior to that of recast Nafion. N(0.8)P(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. (C) 2011 Elsevier B.V. All rights reserved.