Porous composite membrane of PVDF/Sulfonic silica with high ion selectivity for vanadium redox flow battery

Abstract

Porous composite membrane of polyvinylidene fluoride (PVDF)/sulfonic silica with high vanadium ions selectivity was fabricated for vanadium redox flow battery (VRFB) application. The porous PVDF membranes were first prepared as matrix via phase transfer method, followed by introducing sulfonic silica into the matrix via sol-gel process. The sulfonic silica filled in the pores can not only provide proton transfer carriers but also suppress the permeation of vanadium ions through the membrane. Moreover, the organic/inorganic composite can enhance the durability of the membrane. The morphologies of composite membranes (PVDF/SiO2–SO3H) were characterized by SEM technique. Finally, the fabricated composite membrane shows one order of magnitude lower vanadium ion permeability (1.12✕10−7 cm2min−1) and 3 times higher ion selectivity compared with Nafion 115 at room temperature. The single cell assembled using the as-prepared composite membrane gives a Coulombic efficiency of 90.3% and an energy efficiency of 75.6% at a current density of 60 mA cm−2, which is comparable with Nafion 115 (89.7% and 78.2%, respectively). This strategy could provide a simple way to design and fabricate an organic/inorganic composite membrane with high durability for the application in VRFBs.