Morphology and Structure of PEDOT:Nafion: Insights from Experiment and Molecular Dynamics Simulations

ABSTRACT Poly(3,4‐ethylenedioxythiophene) (PEDOT)/Nafion is a promising mixed ionic–electronic conducting polymer. However, in contrast to the well‐studied PEDOT:poly(styrenesulfonate) (PSS) system, the nanoscale morphology and the relationship between crystallinity and composition in PEDOT/Nafion remain insufficiently explored and therefore poorly understood. In this work, we investigate the morphology and structural organization of PEDOT/Nafion by combining X‐ray photoelectron spectroscopy (XPS), X‐ray diffraction (XRD), and coarse‐grained molecular dynamics (MD) simulations. This combined approach enables us to directly link surface composition, bulk crystallinity, and molecular‐scale packing in PEDOT/Nafion—insights that are not accessible from PEDOT:PSS or Nafion‐only studies. XPS revealed two distinct sulfur environments associated with PEDOT and Nafion, with a sulfonic‐acid‐to‐thiophene‐group ratio R S/T of ≈ 2.3. XRD analysis showed PEDOT crystallites with an average π – π stacking size of about 2.1 nm. MD simulations provided molecular‐level insight into the effect of composition, demonstrating that higher Nafion content disrupts PEDOT stacking, yielding smaller crystallites (∼1.1 nm), while reduced Nafion content promotes better ordering (∼1.4–1.8 nm). These findings establish a clear correlation between composition and crystallinity, supporting a model where the surface is Nafion‐rich and the bulk has a lower R S/T ratio. The combined experimental–computational approach offers a comprehensive understanding of PEDOT morphology and valuable guidance for the design of mixed ion–electron conducting polymers.