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 −SO 3 H 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 H 2 SO 4 , 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.