Facile strategy for preparing a novel reinforced blend membrane with high cycling stability for vanadium redox flow batteries

Herein, to resolve issues regarding the long-term stability of cost-effective non-fluorinated membranes for Vanadium redox flow batteries (VRFBs), we design a facile strategy for fabricating a composite membrane based on long-side-chain Sulfonated poly(terphenylene) (SPTP) blended with Polybenzimidazole (PBI). The introduction of PBI in the ether-free SPTP matrix effectively mitigates the transportation of vanadium ions owing to the Donnan repelling effect and the low swelling ratio of the membranes caused by the acid-base interactions between the imidazolium and sulfonic groups. 1H NMR and XPS spectra confirm the chemical structure of the prepared membranes. The optimized membrane achieves a lower area resistance, of 0.34 Ω cm2, as well as a low vanadium permeability, of 1.62 × 10−8 cm2 min−1, in comparison to that of Nafion117 (0.4 Ω cm2 and 4.2 × 10−7 cm2 min−1). Consequently, VRFBs that utilize such membranes exhibit superior coulombic and energy efficiencies—of 99.5% and 86.2% at 100 mA cm−2, respectively—which are an improvement on those of Nafion117 (at 96.1% and 80.9%, respectively). It is important to note that the ether-free backbone, electrostatic repulsion, and reinforcement of PBI greatly improve the mechanical and chemical stability of the blend membranes. Therefore, the C8 membrane presents excellent cycling stability, of up to 1500 charge–discharge cycles, with no significant attenuation in the CE/EE under strong acidic and oxidizing conditions, demonstrating its high physicochemical stability. The results of this study indicate that the SPTP/PBI blend membranes exhibit promising prospects for application in VRFBs.