Sulfonated Graphene Oxide Doped Imidazolium-Functionalized PVDF Ion Exchange Membrane with Enhanced Ion Conductivity

A novel membrane was synthesized in this work by grafting 1-vinyl-3-ethylimidazolium tetrafluoroborate ([C₂VIm][BF₄]) onto a polyvinylidene fluoride (PVDF) backbone, followed by the introduction of a sulfonated graphene oxide (SGO) dispersion into the polymer solution. This composite was transformed into a composite proton-conducting membrane via a solution casting process and subsequently underwent protonation. Successful grafting was confirmed using analytical techniques including Fourier Transform Infrared Spectroscopy (FTIR), ¹H Nuclear Magnetic Resonance (NMR) and X-ray Photoelectron Spectroscopy (XPS). Scanning Electron Microscopy with Energy Dispersive X-ray Spectroscopy (SEM-EDS) analysis verified the homogeneous distribution of the SGO filler. Analysis reveals that incorporating SGO as a filler substantially augments the performance of anion exchange membranes. Key enhancements include a tensile strength increase to 37.97 MPa, water uptake of 10.34%, an ion exchange capacity of 1.68 mmol/g, and the through-plane proton conductivity of 15.47 mS/cm. While vanadium permeability rose marginally to 2.02 × 10^-7 cm²/min, it remains drastically lower than that of Nafion 115. The composite proton-conducting membrane also displayed robust chemical stability. The membrane was finally integrated into a vanadium redox flow battery (VRFB) for performance evaluation. At a current density of 100 mA/cm², it exhibits a satisfactory coulombic efficiency (CE) of 97.84%, excellent capacity retention, and superior cycling stability. These results demonstrate that the PVDF-g-IL/SGO-based composite proton-conducting membrane is an ideal candidate material for vanadium flow battery applications.