Functional Integration in Tailored Polymers Enables Zwitterionic Membranes with Selective Ion Transport and Enhanced Stability

Abstract Aromatic polymer membranes demonstrate commercial potential for vanadium flow batteries (VFBs) owing to their cost‐effectiveness and robust mechanical properties, yet their practical deployment is impeded by inadequate ion selectivity and chemical stability. Here, zwitterionic membranes (SPTIP/PFNP‐x) are engineered by mixing elaborate fluorpoly(aryl pyridine) (PFNP) into sulfonated triptycene‐branched poly(aryl isatin) (SPTIP), achieving a synergistic integration of their complementary advantages. Studies reveal that the cation‐anion interactions between sulfonic and pyridinium groups induce a dense hydrogen‐bonding network, while the 3D triptycene architecture expands polymer chain free volume. This dual‐optimization mechanism enables efficient charge‐balanced ion transport. Simultaneously, the ionic crosslinking structure combined with the Donnan effect from protonated pyridinium effectively suppresses vanadium ion permeation, resulting in exceptional ion selectivity. Furthermore, dual crosslinking from triptycene branching and zwitterionic interactions, coupled with a chemically stable ether‐free backbone and irreversible pyridinium groups, endows the membrane with enhanced mechanical and chemical stability. The optimized membrane empowers VFBs to deliver 83.1% energy efficiency at 200 mA cm −2 , alongside remarkable cycling stability (2000 cycles at 120 mA cm −2 and 500 cycles even at 300 mA cm −2 ). This work presents a novel pathway for designing advanced VFB membranes with precisely tailored structures and multifunctionality.