Highly ion selective hydrocarbon-based membranes containing sulfonated hypercrosslinked polystyrene nanoparticles for vanadium redox flow batteries

The use of organic fillers offers different advantages over inorganic ones, such as better compatibility with the polymer matrix and easier tunability of the degree of sulfonation, and thus of the ion exchange capacity. Composite membranes displayed a significant lowering of the vanadium-ion crossover, yet maintaining high proton conductivity. This result greatly impacted on flow battery self-discharge and on its capacity fading. The first increased from 2 to 7.5 days, while the latter decreased (over 25 cycles) from 8% to 5% for composite membranes with respect to Nafion 212.