Proton-conducting γ-sulfopropyl Acrylate Tethered Halato-Telechelic PVDF Membranes for Vanadium Redox Flow Batteries

Abstract

Advanced fluorinated proton-conducting membrane are dominating functional macromolecules due to their high performance in electrochemical energy devices. However, the co-ion leakage and low power densities still proposes a challenge. Herein, a novel functionally tailored polyvinylidene fluoride-co-(γ)-sulfopropyl acrylate (PVDF-g-SA) based proton-conducting membrane is prepared for vanadium redox flow batteries (VRFBs). The approach introduces a facile guideline to design halato-telechelic −SO₃H architectures by tethering γ-sulfopropyl acrylate onto dehydrofluorinated PVDF. The optimized PVDF-g-SA-15 exhibits proton conductivity (κ_m^H+) of 17 mS cm⁻¹ (akin Nafion: ~19 mS cm⁻¹) and retained 87 % and >95 % of its properties in Fenton's reagent and 3 M H₂SO₄, respectively. In VRFB device, the PVDF-g-SA-15 shows ∼98 % capacity utilization outperforming Nafion-117 (∼85 %). Moreover, bearing dense ionic orientation (viz AFM phases), the potential drop rate is ~2× lower for PVDF-g-SA-15 (1.4×10⁻³ V min⁻¹) than that of Nafion-117 (2.6×10⁻³ V min⁻¹). Operational endurance is evaluated fit for 150 mA cm⁻² showing maximum coulombic, energy and voltage efficiencies of >98 %, ∼78 %, ∼80 %, respectively. Further investigation for ~200 cycles infer excellent durability with ∼95 % property retention. Additionally, the PVDF-g-SA-15 can deliver ~20 % higher power density than Nafion-117 does. Thus, the revealed alternate membrane holds promising utility in VRFB applications.