Direction dictates function: Aligned sulfonated MoS₂ nanosheets architect tortuous vanadium mazes and proton highways for ultrahigh membrane selectivity

Ion-selective membranes critically govern vanadium redox flow battery (VRFB) performance by facilitating proton conduction while suppressing detrimental vanadium-ion crossover, however, these properties are often difficult to reconcile. To overcome this limitation, a sulfonated poly(ether ether ketone)/polyaniline/s-MoS₂ composite membrane featuring highly oriented sulfonated MoS₂(s-MoS₂) nanosheets is engineered. The large basal planes of nanosheets are aligned parallel to the membrane surface using volatilizing shear flow-induced alignment. This strategic design establishes dual barriers, including electrostatic repulsion to reject vanadium ions and steric hindrance by creating tortuous transport, effectively reduce vanadium permeability, while abundant sulfonic acid groups construct continuous proton transport channels. Such a synergistic architecture achieves superior ionic selectivity (3.82 × 10⁴ S min cm⁻³), representing an order-of-magnitude improvement over Nafion 212 membranes while maintaining high proton conductivity. Molecular dynamics simulations further confirm hydronium ion diffusion pathways dominated by aligned s-MoS₂ and elucidate the role of polyaniline in optimizing channel geometry. Consequently, VRFBs integrating this membrane exhibit 84.8% energy efficiency after 600 cycles at 120 mA cm⁻², demonstrating remarkable cycling stability with 70.8% capacity retention at the 100th cycle. This breakthrough establishes a versatile membrane design paradigm that successfully reconciles traditionally incompatible transport properties, opening new avenues for advanced energy conversion technologies.