Synergistic chemical/physical regulation of ion transport in sPIM-1/Nafion membranes enables high-performance vanadium flow batteries

Vanadium flow batteries (VFBs) are considered a promising technology for grid-scale energy storage owing to their intrinsic safety, flexible design, and long cycle life. However, their practical deployment remains constrained by the selectivity–conductivity dilemma of benchmark membranes such as Nafion, leading to capacity decay and efficiency loss. Herein, we propose and experimentally fabricate a hybrid membrane integrating a sulfonated polymer of intrinsic microporosity (sPIM-1) into Nafion. Through systematic optimization of sPIM-1 loading, the optimal 7% sPIM-1/Nafion membrane achieves an exceptional ion selectivity (1.95 × 10 5  S min cm −3 , 2.87 times larger than conventional Nafion), while retaining high proton conductivity (210.96 mS cm −1 ). As a result, VFBs assembled with the composite membrane exhibit a markedly prolonged self-discharge time (70.7% extension) and outstanding cycling durability, retaining an energy efficiency of 86.6% after 1000 cycles, substantially outperforming Nafion-based systems. The improvement is rationalized by the synergistic coupling of chemical (-SO₃H mediated) and physical (rigid-porous-network) proton transport pathways, concurrent with a size-sieving effect that selectively blocks vanadium ions. This work not only demonstrates the efficacy of sPIM-1/Nafion composite membrane strategy for high-performance VFB, but also establishes an advanced membrane design avenue in energy storage devices.