Versatility of sulfonated poly (vinylidene fluoride-co-hexafluoropropylene) membranes incorporated with sulfonated octaphenyl polyhedral oligomeric silsesquioxane for vanadium redox flow battery applications

Hybrid membranes are fabricated using the blends of sulfonated poly (vinylidene fluoride-co-hexafluoropropylene) (SPVDF-co-HFP) and sulfonated octaphenyl polyhedral oligomeric silsesquioxane (SOPS) as an alternate for expensive Nafion in vanadium redox flow battery (VRFB) applications. The FT-IR and TEM investigation indicates the successful sulfonation of OPS and uniform distribution of SOPS. The morphological study of hybrid membranes by SEM-EDX and FESEM revealed the excellent dispersing ability of SOPS on a SPVDF-co-HFP matrix. The physicochemical analysis of SPVDF-co-HFP/SOPS membranes demonstrated an increase in hydrophilic ion-exchangeable sites. The SPVDF-co-HFP/SOPS (0.5 wt.%) membrane displayed a maximum proton conductivity of 6.27 x 10(-3) Scm(-1) at 80 degrees C because of strong hydrogen bond formation between SPVDF-co-HFP and SOPS facilitates proton migration. Besides, the cage-like structure of SOPS effectively shields vanadium-ion permeation to 1.21 x 10(-8) cm(2) min(-1) and thus, showed a maximum membrane selectivity of 43.05 x 10(4) Scm(-3) min. Overall, the hybrid membranes of SPVDF-co-HFP/SOPS were considered to be a better substitute for Nafion in VRFBs.