Balancing Hydrophobicity and Hydrophilicity: Dual Filler‐Engineered Proton Exchange Membranes for Durable, High‐Power Fuel Cells

Most filler materials in ion‐exchange membranes have been employed primarily to increase water uptake, with limited control over polymer morphology. Here, we direct the structural evolution of perfluorosulfonic acid (PFSA) membranes through PFSA–filler interface engineering, using zirconium‐based metal–organic frameworks (MOFs) with systematically tuned surface polarity. Hydrophilic MOF surfaces stabilize interfacial hydration layers that promote water‐cluster expansion and interdomain bridging across the membrane, whereas hydrophobic MOF surfaces preferentially interact with the PTFE backbone, inducing parallel chain alignment, lowering bulk crystallinity, and generating compact water channels. A dual‐filler Nafion membrane combining hydrophilic UiO‐66 and hydrophobic UiO‐67 integrates both effects, achieving a significantly enhanced proton conductivity (176 mS cm −1 at 80°C, 95% RH), peak power densities of 785.3 mW cm −2 (ambient pressure) and 1,456 mW cm −2 (200 kPa), and a threefold improvement in durability compared to Nafion. Because the total filler content remains below 4 wt.%, this polarity‐guided strategy is compatible with industrial roll‐to‐roll fabrication and offers a general design rule for next‐generation, high‐performance and durable fuel‐cell membranes.