An ultrahigh conductivity and efficiency of SPEEK-based hybrid proton exchange membrane containing amphoteric GO-VIPS nanofillers for vanadium flow battery

Sulfonated poly(ether ether ketone) (SPEEK)-based hybrid membranes (S/GO-VIPS) have been fabricated by the solution blending method, which amphoteric GO-VIPS nanofillers prepared by grafting 3-(1-vinyl-3-imidazole) propane sulfonate (VIPS) onto graphene oxide (GO) flake. With various GO-VIPS contents changing from 1 to 10 wt% in the S/GO-VIPS membranes, the interfacial interaction between SPEEK and GO-VIPS contributes to enhanced membrane structures and performance. Against pristine SPEEK (3.9 × 103 S min cm−3) and Nafion 117 (4.0 × 103 S min cm−3), S/GO-VIPS-5 gives the highest ion selectivity at 24.4 × 103 S min cm−3, demonstrating the amphoteric GO-VIPS nanosheets afford a superior vanadium ion resistance and proton conductivity. At 100–200 mA cm−2 current density, S/GO-VIPS-5 presents excellent coulombic efficiency (97.4–99%), energy efficiency (78.9–66.3%), and self-discharge time (78 h), which is better than that of SPEEK and Nafion 117, respectively. Further cycling at 100 mA cm−2 for 350 times, its energy efficiency maintains at 80%, confirming its excellent structural stability and chemical stability. Combining with the physical barrier and the amphoteric acid-base functional groups of the GO-VIPS nanosheets, the increased proton conductivity and ion selectivity, and the decreased permeability of SPEEK-based membranes are well-regulated, demonstrating a promise in developing high-performance proton exchange membrane for vanadium flow battery applications.