Effect of surface wettability on liquid water freezing behavior in the gas diffusion layer of proton exchange membrane fuel cells

During the operation of proton exchange membrane fuel cells (PEMFCs), particularly under low-temperature cold-start conditions, the freezing of liquid water within the gas diffusion layer (GDL) can significantly impair both the performance and structural stability of the cell. Therefore, effective water management strategies are essential. This study combines high-fidelity numerical simulations and in situ cryo-microscopy to systematically investigate the impact of carbon fiber structure on the dynamic transport characteristics of liquid water on the GDL surface. Additionally, the influence of GDL surface wettability and carbon fiber structure on the freezing behavior of liquid water is explored. The results show that by adjusting fiber spacing and surface wettability, it is possible to control the diffusion behavior of liquid water within the GDL and reduce the risk of flooding. Hydrophilic GDLs promote a uniform water distribution throughout the pore structure and facilitate a continuous freezing process. In contrast, hydrophobic GDLs result in discrete droplet freezing and abrupt pore blockage. The hydrophobic GDL reaches a peak ice coverage of 18% at −15 °C, while the hydrophilic GDL shows a sharper increase, reaching 26% at −30 °C after steadily increasing to −20 °C. These differences are attributed to variations in surface wettability and fiber-scale wetting interactions between the two materials. The findings emphasize the critical role of wettability in directing ice growth pathways and maintaining the structural integrity of the GDL. This study offers valuable theoretical insights for optimizing GDL design and provides experimental evidence for improving the cold-start performance of PEMFCs.