Abstract: Vanadium redox flow batteries (VRFB) are regarded as one of the most promising technologies for massive electrical energy storage for renewable energy and energy-saving processes. Such devices have the merits of long lifespan, simple configuration and independent power and capacity ratings and have abstracted significant attention in recent years. Proton conducting membrane one of the key components in VRFB systems, plays the role of conducting protons during charge/ discharge cycles, and prevents vanadium ions from direct contact between the positive and negative half-cell electrolytes. To achieve high energy efficiency, long life and low cost of a VRFB stack, the membrane should meet the requirements of high conductivity, chemical and mechanical resistance, low permeability of vanadium ions and affordable cost. We introduce polymeric hydrophilic/hydrophobic interactions into membrane formation, and propose a general and straightforward strategy for preparing membranes with nanometer-scale pores. Poly(vinylidene fluoride) (PVDF) and sodium allyl sulfonate (SAS) are used respectively as the membrane material and pore-generator, which offer chemically stable and oxidation-resistant membranes with various potential applications. We have been able to scale up the manufacture process to produce membranes of area of 800×900mm, thickness of 60~150 μm and conductivity around 3×10^-2 S/cm. VRFB stacks with the membranes have been shown to have an energy efficiency about 72% for a 8 kW system.

Key words: VRFB, proton conduction membrane, conductivity, poly(vinylidene fluoride)