Blend membranes of sulfonated poly(ether ether ketone) (SPEEK) and poly(vinylidene fluoride) (PVdF) are prepared with various mixing mass ratios for vanadium redox flow battery application for the first time. The SPEEK/PVdF blend membranes are characterized by scanning electron microscopy and energy dispersive X-ray spectroscopy. The water uptake, swelling ratio, ion exchange capacity, proton conductivity, VO2+ permeability, ion selectivity, single cell performance and mechanical property of blend membranes are detailed evaluated. The blend membranes are dense and uniform when PVdF mass ratio ranges from 5 wt.% to 20 wt.%. The blend membrane with 15 wt.% PVdF (denoted as S/P 15) is further investigated for its good balance of proton conductivity and ion selectivity. The cell with S/P 15 membrane shows higher coulombic efficiency and energy efficiency compared with Nafion 117 membrane (98.0% vs. 92.0% and 81.0% vs. 75.8%, respectively). Furthermore, no obvious efficiency declines are observed after 80 cycles cell test accompanied with a lower discharge capacity decay rate. (C) 2013 Elsevier B.V. All rights reserved.