Cellulose Nanofibers Derived From Sea Squirt Tunics for Enhancing PEM Fuel Cells Performance via Pt/C–Ionomer Agglomerate Engineering

ABSTRACT In this study, high‐aspect‐ratio cellulose nanofibers (CNFs) are extracted from sea squirt tunic via acid hydrolysis and use as nanofillers in the cathode catalyst layers (CLs) of polymer electrolyte membrane fuel cells (PEMFCs). Because of the aqueous‐based extraction process, CNFs possess numerous hydrophilic functional groups on their surfaces, enabling their excellent dispersibility in organic solvents. By leveraging both the high aspect ratio and hydrophilic surface characteristics of CNFs, membrane electrode assemblies (MEAs) incorporating 9 wt.% CNFs exhibit significantly enhanced power performance at low current densities compared to pristine MEAs. This improvement is attributed to the reduction in the agglomerate size within the cathode CL, which facilitates oxygen transport to the catalyst surface and consequently enhances the catalytic activity. Furthermore, surface and interfacial cutting analysis system (SAICAS) measurements confirm that the incorporation of CNFs improves the mechanical integrity of the cathode CLs. Geodict simulation results further reveal that CNFs promote favorable changes in the pore structure, improving gas diffusion and thus supporting efficient catalyst activation. Collectively, these findings suggest that the introduction of properly functionalized 1D nanofibers is a highly effective approach for developing high‐performance CLs for PEMFCs.