A Highly Porous Nanofibrillar PEDOT:PSS Matrix for Beyond‐Surface Precious‐Metal Utilization and Volumetric Electrocatalysis

ABSTRACT Efficient precious‐metal utilization in electrocatalysis requires electrically conductive support architectures that enable electrocatalytic activity beyond conventional surface‐limited designs. Herein, we demonstrate that solvent‐assisted crystallization converts poly(3,4‐ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) into a water‐stable, highly conductive nanofibrillar matrix featuring nanoscale porosity and controlled swelling. During the subsequent electrodeposition of Pt nanoparticles (NPs), the highly porous nanofibrillar PEDOT:PSS moderately swells in aqueous media, allowing Pt ions to deeply infiltrate the polymer network and form uniformly dispersed Pt NPs throughout the entire film volume rather than on the surface alone. This volumetric nanoconfinement effect yields a markedly enlarged electrochemically active surface area (20 m ² g _Pt ⁻¹ ), rapid reactant permeability, and structural robustness under operating conditions. The resulting PEDOT:PSS–Pt nanocomposite exhibits greatly enhanced catalytic activity for hydrogen evolution and methanol oxidation reactions, outperforming conventional planar Pt architectures. This work establishes highly porous nanofibrillar PEDOT:PSS as a previously underutilized volumetric electrocatalyst scaffold and provides a general design strategy for maximizing precious‐metal efficiency in electrocatalysis and water‐splitting systems.