Comprehensive analysis of PTFE distribution in gas diffusion layers using advanced ex-situ and in-situ characterization techniques

Abstract

The performance and longevity of Proton Exchange Membrane Fuel Cells (PEMFCs) are critically dependent on the properties of the gas diffusion layer (GDL). This study investigates the hydrophobic treatment using the dip coating method on two types of GDLs, namely dry-laid and wet-laid, using polytetrafluoroethylene (PTFE) at target concentrations of 5 wt%, 20 wt%, and 50 wt%. The distribution of PTFE across the thickness and surface of the GDLs is characterized to understand its impact on water management and gas transport properties. The effectiveness of the hydrophobic treatment is evaluated both ex-situ via contact angle measurements and in-situ by limiting the current density to assess oxygen transport resistance. Additionally, advanced characterization techniques, including Scanning Electron Microscopy (SEM), Energy Dispersive X-ray Spectroscopy (EDX), and Raman Spectroscopy, are employed to provide a detailed analysis of PTFE distribution, correlating these findings with the GDL’s performance in operating PEMFCs.

**Key findings** reveal that while increased PTFE concentration improved hydrophobicity and water management, excessive PTFE loading led to pore blockage, negatively impacting oxygen transport resistance. The wet-laid GDL demonstrated more uniform PTFE distribution and higher transport resistance compared to the dry-laid GDL. These insights emphasize the importance of balancing PTFE concentration to optimize both water management and gas diffusion in PEMFCs.