In order to reduce the permeation of vanadium ions across the ion exchange membrane during the operation of vanadium redox flow battery (VRB) based on Nation membrane, the interfacial polymerization was applied to form a cationic charged layer on the surface of Nation 117 membrane. The area resistance and the permeability of vanadium ions were measured. The results indicate that comparing with the unmodified Nation membrane, the modification of Nation membrane results in a dramatic reduction in crossover of vanadium ions across the membrane and a little higher area resistance of the membrane. As a result, the columbic efficiency for the VRB single cell based on the modified Nation membrane(VRB-modified Nafion), which is related to the concentration of the incubation solution of polyethylenimine (PEI), was increased significantly. The value is 96.2-97.3%, which is higher than that obtained with the VRB single cell based on unmodified Nafion membrane(VRB-Nafion) (around 93.8%). Due to the little higher area resistance caused by the modification, the voltage efficiency of VRB-modified Nafion is lower than that of VRB-Nafion. Furthermore, the water transfer across the modified membrane was also reduced. The ion exchange capacity (IEC) of the modified Nation membrane was also evaluated. The formation of the thin cationic charged layer on the membrane surface was confirmed by IR spectra analysis. (C) 2007 Elsevier B.V. All rights reserved.