Advanced Poly(vinyl chloride)-Based Membranes Functionalized with Amino Compounds for Vanadium Redox Flow Batteries

Developing high-performance membranes for vanadium redox flow batteries (VRFBs) faces significant challenges. This study explores poly(vinyl chloride) (PVC) as a membrane matrix for VRFBs due to its cost-effectiveness, excellent membrane-forming properties, and strong tensile resistance. Six amino compounds, including 1-propanamine (A1), 3-(dimethylamino)propylamine (A2), 1-(3-aminopropyl)pyrrolidine (A3), 1-(3-aminopropyl)-2-pyrrolidinone (A4), 1-(2-aminoethyl)-4-methylpiperazine (A5), and N-aminoethylpiperazine (A6), are used to functionalize PVC through nucleophilic reactions. Among these, the PVC-A6 membrane, with bis-functional sites, shows a remarkable acid doping capability (89.3%), good mechanical strength (5.6 MPa), low area resistance (0.32 Ω·cm2), and superior vanadium ion resistance (2.99 × 10–7 cm2 min–1), resulting in an ion selectivity three times higher than Nafion 115. The PVC-A6 membrane's technical feasibility was demonstrated in VRFB applications. Compared to Nafion 115, the VRFB with PVC-A6 exhibits significantly higher cell efficiencies across current densities from 60 to 160 mA cm–2 and superior cyclic stability, indicating that economically friendly PVC-Ax membranes hold great potential for VRFB applications.