Innovations and prospects on functional membrane design for advanced redox flow batteries

Conventional membrane design for redox flow batteries (RFBs) faces persistent challenges in balancing the conductivity–selectivity–stability trilemma, particularly with perfluorinated benchmark materials suffering from high cost, redox couple crossover, and environmental concerns. Recent advances demonstrate that microstructure engineering and novel chemistries, including charged/uncharged nanochannels, size-exclusion architectures, and hybrid systems, enable breakthrough performance. However, comprehensive reviews linking these innovations to commercialization barriers remain limited. This review presents a novel synthesis of recent advances in RFB membrane design by structurally categorizing membranes into dense, porous, and charged microporous types, and highlights innovative strategies that overcome the classic conductivity–selectivity–stability trade-off. We first establish the fundamental ion transport mechanisms and performance trade-offs governing membrane efficiency; multifunctional chemistries and microstructural control of RFB membranes are also analyzed. Subsequently, we categorize membrane architectures into dense and porous configurations based on structural features, and highlight recent innovations that overcome conductivity-selectivity compromises through Donnan exclusion in charged dense membranes, size sieving in porous membranes, and the synergy between the two in charged porous membranes. Finally, we discuss unresolved challenges in long-term stability, scalability, performance validation, and integrated system design, providing a roadmap for future research focused on operando characterization, bio-inspired multifunctional materials, and system-specific optimization. This review establishes design principles for next-generation RFB membranes that simultaneously achieve high efficiency, durability, and eco-compatibility in grid-scale energy storage.