Interfacial Engineering Architecture of Isatin-Derived Polymer-Tethered Polyoxometalates and Their Application in Sulfonated Poly(aryl ether ketone) Proton Exchange Membranes

This study presents an interface engineering strategy for the fabrication of high-performance proton exchange membranes. The strategy utilizes isatin-derived polymer (PIB)-anchored Keggin-type phosphotungstic acid (H₃PW₁₂O₄₀, abbreviated as PW) as functional fillers, which are integrated into a sulfonated polyaryletherketone (named as SPAEK) matrix to synergistically enhance the overall performance of the resulting membrane (denoted as PISm/PW-x, where m represents the mass ratio of PIB to SPAEK and x represents the mass fraction of PW in the hybrid matrix). The poly(1,2-diphenylethane)-isatin (named as PIB), synthesized via superacid catalysis, forms a strong ionic cross-linking (-NH···-SO₃H) with SPAEK, achieving outstanding mechanical strength (46.1 MPa) and dimensional stability (6.25% swelling ratio at 80 °C), while the uniformly dispersed PW clusters act as bridges to construct a continuous hydrogen-bonding network, enhancing the proton conductivity (0.192 S cm^-1 at 80 °C) by 2.15 times compared to the pristine membrane in water solution. The optimized PIS1/PW-8 membrane demonstrates exceptional overall performance, characterized by ultra-restricted methanol permeability (1.82 × 10^-8 cm² s^-1), superior oxidative stability (99.4% weight retention in Fenton's test), and outstanding operational durability (sustained conductivity over 100 h at 80 °C). This performance is attributed to a well-defined microphase-separated morphology featuring approximately 2.0-3.0 nm hydrophilic domains and highly efficient proton hopping pathways. This molecular-level engineering of organic-inorganic interfaces offers a paradigm for advanced fuel cell membranes, simultaneously addressing the long-standing trade-off between conductivity and mechanical stability in polyelectrolyte materials.