Magnetic field aligned carbon nanotube networks for structurally optimized cathodes catalyst layer of polymer electrolyte membrane fuel cells

• PSS coating improves CNT-Fe₃O₄ dispersion and thermal stability. • Magnetic-field-assisted drying aligns CNTs, enhancing pore structure and transport. • Optimized CNT alignment boosts MEA performance and durability. The oxygen diffusion resistance and inefficient water removal in conventional cathode catalyst layers (CLs) in polymer electrolyte membrane fuel cells (PEMFCs) restrict their performance at high current densities despite the presence of large pores in the cathode CL. To resolve these issues, a polystyrene sulfonate (PSS)-coated CNT-Fe 3 O 4 (PSS@CNT-Fe 3 O 4 ) was introduced for preventing agglomeration and facilitating precise pore control under a magnetic field. This study investigated the effect of the orientation of the magnetic field on the drying position of PSS@CNT-Fe 3 O 4 and its impact on the performance of the cathode CL. A CL dried under a bidirectional magnetic field applied from both the top and bottom achieved the highest performance in the high current density region (2.0 A cm –2 at 0.4 V). This improvement was attributed to the continuous distribution of pores in the cathode CL, with no ionomer imbalance. In contrast, the ionomer and catalyst became unevenly distributed when the CL was dried with a magnetic field applied from just one direction (either top or bottom), thereby resulting in reduced performance: 1.54 A cm –2 at 0.4 V (bottom) and 1.87 A cm –2 at 0.4 V (top). These findings suggest the potential of the proposed approach for enhancing the mass transport efficiency of cathode CLs for PEMFCs.