Sol-gel derived Nafion/SiO2 hybrid membrane is prepared and employed as the separator for vanadium redox flow battery (VRB) to evaluate the vanadium ions permeability and cell performance. Nafion/SiO2 hybrid membrane shows nearly the same ion exchange capacity (IEC) and proton conductivity as pristine Nation 117 membrane. ICP-A-ES analysis reveals that Nafion/SiO2 hybrid membrane exhibits dramatically lower vanadium ions permeability compared with Nation membrane. The VRB with Nation/SiO2 hybrid membrane presents a higher coulombic and energy efficiencies over the entire range of current densities (10-80 mA cm(-2)), especially at relative lower current densities (< 30 mA cm(-2)), and a lower self-discharge rate compared with the Nation system. The performance of VRB with Nafion/SiO2 hybrid membrane can be maintained after more than 100 cycles at a charge-discharge current density of 60 mA cm(-2). The experimental results suggest that the Nafion/SiO2 hybrid membrane approach is a promising strategy to overcome the vanadium ions crossover in VRB. (c) 2007 Elsevier B.V. All rights reserved.