Robust Sulfonated Proton Exchange Membrane from a Poly(styrene-co-divinylbenzene) melt-Interpenetrated Polyethylene Network for Vanadium Redox Flow Batteries

A low-cost, durable, and efficient proton exchange membrane has been developed via melt-interpenetrating-type networking of poly(styrene-co-divinylbenzene) and polyethylene for vanadium redox flow battery (VRFB) application. The pristine poly(styrene-co-divinylbenzene) interpenetrating polyethylene films were processed using blow-molded extrusion, and the sulfonic acid groups were functionally tailored via a simple room-temperature immersion method. The designed membranes exhibited excellent physicochemical properties and mechanical stabilities in an electrochemical environment. Compared to Nafion-117 (N-117, 41 mΩ), the interpolymer membrane exhibited a cell resistance of ∼26 mΩ and demonstrated high Coulombic efficiency, energy efficiency, and voltage efficiency in the ranges of 93–97, 86–68, and 93–71% when operated between current densities of 50–200 mA cm–2, respectively. Moreover, the kinetic limitations of V3+↔V2+ conversion were simultaneously addressed using cat. d-fructose in negolyte via transient tailored wettability. With negolyte modifications, the interpolymer membrane illustrated a high specific capacity recovery of ∼98% when operated at 100 mA cm–2 employing a rebalancing method. At 50 mA cm–2 and 100 mA cm–2, the membrane achieved capacities of ∼26 and 25 Ah L–1, which were ∼96 and 93% of theoretical limits (viz., 26.8 Ah L–1), respectively. Polarization studies revealed the highest peak power density to be ∼570 mW cm–2, wherein N-117 illustrated capacity, peak power density, and energy efficiencies of 21 Ah L–1, ∼375 mW cm–2, and 80%, respectively. Thus, simultaneous benchmarking in membrane material design and V2+↔V3+ kinetic limitations were successfully demonstrated to corroborate strong competitive performance for ready-to-scale VRFB devices.