Freezing behaviors of supercooled water in PEMFC gas diffusion layers regulated by wettability and saturation: infrared-electrical diagnosis and physics-based predictions

Freezing of residual water in gas diffusion layers (GDLs) constrains the gas transport and cold-start reliability in proton exchange membrane fuel cells (PEMFCs). This study investigates the supercooled-water freezing behaviors in TORAY H-060 GDLs with different wettability and water saturations using infrared thermography and temperature-dependent electric resistance measurements. The dynamic local nucleation is characterized by infrared thermography, which shows that hydrophilic GDLs promote connected liquid pathways, leading to dominant-site nucleation and rapid recalescence propagation, whereas hydrophobic GDLs confine water into isolated clusters, resulting in distributed nucleation and dispersed latent-heat release. Resistance measurements capture freezing-induced changes in the overall conductive network and provide a bulk transition temperature complementary to the local nucleation temperature identified by infrared thermography. The supercooling degree at nucleation ranges from approximately 2 to 12 °C, which are dependent on the wettability and water saturation. Generally, the nucleation temperature is lower in hydrophobic GDLs and decreases with increasing saturation. A heterogeneous-nucleation-based correlation is further developed to predict nucleation temperature of supercooled water in GDLs as a function of wettability and saturation, providing experimental criteria for PEMFC cold-start modeling.