Breaking the Conductivity–Selectivity Trade-off in Nafion via Synergistic Molecular Modification for High-Performance Vanadium Redox Flow Batteries
Developing ion exchange membranes with both high proton conductivity and high selectivity is crucial for vanadium redox flow batteries (VRFBs). Commercial Nafion membranes suffer from severe vanadium crossover, while conventional additives often aggregate, disrupting ion domains and significantly reducing proton conductivity. To overcome this conductivity–selectivity trade-off, we propose a modification strategy based on molecular-level functional strategy. Two complementary additives, polyvinylpyrrolidone (PVP) and a fluoroalkyl-grafted polyoxometalate cluster (8FSiW11), are introduced into Nafion matrix to achieve precise, cooperative, regulation of ionic domains. PVP fills ion domains via hydrogen bonding and electrostatic interactions, constructing an efficient barrier against vanadium ions. Simultaneously, 8FSiW11 anchors at the hydrophilic/hydrophobic interface, providing additional proton sources and hopping sites to compensate for proton neutralization by PVP. The resulting hybrid membrane exhibits a proton/vanadium selectivity of 1×10^6 S min cm^-3, 8.6 times higher than commercial Nafion 212 (NR212), and enables VRFB energy efficiencies (EE) of 88.9% at 100 mA cm^-2 and 83.2% at 200 mA cm^-2. This work demonstrates the potential of synergistic molecular modification strategy to break conductivity–selectivity trade-off in membrane design for next-generation high-performance VRFBs.