Overcoming Thickness–Durability Trade‐Off in PEM Fuel Cells via Stretched PTFE Nanofiber‐Reinforced Composite Membranes

Abstract Reinforced composite membranes (RCMs), composed of electrospun porous nanofiber (NF) and perfluorosulfonic acid (PFSA), have garnered considerable attention for achieving high durability in proton exchange membrane (PEM) fuel cells. However, electrospinning faces critical challenges in producing thin NF mats essential for fabricating ultrathin RCMs that reduce ohmic resistance. Herein, thermomechanical stretching is presented to fabricate ultrathin polytetrafluoroethylene (PTFE) NF‐based reinforcements. Stretching the PTFE NF by 2‐ and 3‐fold not only reduces their thickness but also increases porosity, facilitating efficient PFSA impregnation. Notably, the 3‐fold stretched PTFE‐based RCM (3‐sPTFE RCM), with ultrathin thickness (<20 µm), exhibits minimal swelling in the hydrated state compared to commercial Nafion XL. The 3‐sPTFE RCM‐adopted cell demonstrates exceptional performance under various relative humidity conditions, achieving a current density of 2.79 A cm −2 at 0.6 V and a maximum power density of 1.99 W cm −2 . Furthermore, the 3‐sPTFE RCM maintains long‐term operational durability, with low hydrogen crossover current (<3 mA cm −2 at 0.4 V) even after 21,000 wet/dry cycles, exceeding the U.S. Department of Energy (DOE) durability targets for automotive membrane applications. This fabrication strategy for ultrathin PTFE NF reinforcements offers a promising pathway toward the next generation of high‐performance and durable PEM fuel cells.