From Photons to Polymer Networks: How UV and Glutaraldehyde Modify Nafion Membranes Differently Across 50–180 μm

ABSTRACT Controlling ion transport in polymer electrolyte membranes (PEMs) without compromising structural integrity remains a central challenge for polymer electrolyte membrane fuel cells (PEMFCs). Although Nafion is the benchmark PEM, its performance is tightly coupled to thickness‐dependent water management and morphological organization. Here, we demonstrate that UV irradiation provides a controllable, thickness‐sensitive means to tune proton transport via spatially resolved photochemical activation without altering the polymer backbone chemistry. Across 50, 90, and 180 μm Nafion membranes exposed to 100–250 mJ/cm 2 UV doses, FTIR confirmed preservation of the PFSA backbone, while FESEM revealed smoother membrane morphology after UV irradiation. The 90 μm membrane exhibited the highest proton conductivity (247.6 mS/cm) compared with untreated Nafion (123.1 mS/cm), whereas GA treatment improved structural stability but reduced proton conductivity. Beer–Lambert modeling ( α = 287.82 cm −1 ) yielded a UV penetration depth of 34.7 μm, explaining the thickness‐dependent effect. UV‐treated membranes also showed improved mechanical performance and highest oxidative stability, exhibiting only 12.99% weight loss after 48 h. These results establish the thickness‐to‐penetration‐depth ratio ( L / δ ) as a useful design parameter for membrane modification, providing a scalable strategy to improve proton transport and durability.