Long side-chain imidazolium functionalized poly(vinyl chloride) membranes with low cost and high performance for vanadium redox flow batteries

Abstract

Developing polymer membranes with low price, superior ion conduction and good vanadium ion transport resistance is currently a hot topic in vanadium redox flow batteries (VRFBs). In the present work, long side-chain imidazolium functionalized poly(vinyl chloride) (PVC) membranes are fabricated to provide a versatile strategy for the ion transport and selectivity trade-off in VRFBs. PVC is employed as the membrane matrix owing to its low price, high tensile strength and natural chlorine groups. 1-(3-Aminopropyl) imidazole (APIm) is grafted into PVC via a facile nucleophilic reaction, which provides the basic groups as the interaction sites for sulfonic acid, resulting in low area resistance. Meanwhile, due to the electrostatic repulsion effect of positively charged imidazolium cations between vanadium ions, APIm-PVC membranes display low vanadium ion permeability. Consequently, the 80 %APIm-PVC membrane has both low area resistance of 0.268 Ω∙cm2 and low vanadium ion permeability of 9.0 × 10−8 cm2∙min−1 simultaneously, achieving a 5 times higher ion selectivity (2.65 × 105 S min cm−3) than Nafion 115 (0.52 × 105 S min cm−3). The VRFB equipped with the 80 %APIm-PVC membrane shows higher battery efficiencies than the cell with Nafion 115 ranging from 100 to 160 mA∙cm−2, and also possesses excellent cycle constancy, indicating that low-cost x%APIm-PVC membranes have a great application potentiality for VRFBs.