Effect of Cathode Catalyst Layer Thickness on PEMFCs Performance: Carbon Support Matters

Abstract The influence of catalyst layer thickness on the performance of proton exchange membrane fuel cells (PEMFCs) was investigated under a constant roughness factor, with emphasis on a comparative analysis between catalysts made from solid carbon and porous carbon supports. For both porous and solid carbon supports, an excessively thick cathode catalyst layer (CCL) resulted in an elongated oxygen transport path and a substantial increase in mass transport resistance. The performance of thin CCL was fundamentally determined by the carbon support structure: porous carbon was highly susceptible to liquid water flooding in thinner layers, as its intricate pore network significantly impeded water removal and drastically elevated oxygen transport resistance. In contrast, the solid carbon support with limited porosity effectively mitigated flooding. Characterized by minimal primary pores, the solid carbon support suppressed vapor condensation and facilitated rapid water expulsion, enabling the fuel cell to sustain high performance even with a thin CCL of ∼3.7 μm. Meanwhile, variations in anode catalyst layer thickness had a negligible impact on the performance, even under ultra-low platinum loadings (0.015 mgPt cm-2). These findings underscore that tailored optimization of the CCL thickness based on the carbon support structure is critical for developing high-performance PEMFCs by minimizing oxygen transport resistance