Ultrathin Nafion-filled porous membrane for zinc/bromine redox flow batteries

In this work, we present a 16 μm-thick Nafion-filled porous membrane for Zn/Br redox flow batteries (ZBBs). By using molecular dynamics simulation and dynamic light scattering analysis, we rationally design Nafion solution for Nafion impregnation into a porous polypropylene (PP) separator. A void-free Nafion/PP membrane is successfully fabricated by using NMP as a solvent for the Nafion solution. The resulting membrane shows a smaller area specific resistance in comparison with 600 μm-thick, commercial SF-600 porous membrane. Due to its dense morphology, Br(2) diffusivity of the Nafion/PP membrane is two orders of magnitude lower than that of SF-600, resulting in a comparable Br(2) crossover in spite of 37.5 times smaller membrane thickness. As a result, the ZBB based on the Nafion/PP membrane exhibits a higher energy efficiency, demonstrating that ion exchange membrane can outperform the conventional porous membrane by reducing the membrane thickness with inexpensive porous substrate.