Wettability Determination of Gas Diffusion Layers for Polymer Electrolyte Fuel Cells

Effective water management in polymer electrolyte fuel cells (PEFCs) critically depends on the wettability of gas diffusion layers (GDLs), which controls capillary-driven liquid transport. While hydrophobic coatings (like polytetrafluoroethylene, PTFE) are widely used to tailor wettability, detecting and quantifying their distribution within the complex porous structure remains challenging. Wettability characterization serves as an indirect proxy but is complicated by the coupled effects of pore morphology and surface chemistry, even though effective contact angles remain a required input for capillary transport models. This work summarizes experimental and modeling approaches for GDL wettability assessment. Conventional techniques (sessile drop, Wilhelmy plate) provide surface-level information, whereas bulk methods (Washburn, capillary pressure-saturation (p c –S) curves, capacitance) capture macroscopic behavior but lack spatial resolution. Advanced imaging-based methods, such as environmental scanning electron microscopy and X-ray tomography with image-based contact angle analysis, enable 3D insight yet remain resource-intensive. Furthermore, the widespread concept of “mixed wettability,” attributed to inhomogeneous PTFE coating, is examined and the influence of pore geometry is highlighted, supported by pore-network modeling approaches. Together, these approaches reveal how pore geometry and surface chemistry jointly define GDL wettability.