Effects of Hydrophobicity Treatment of Gas Diffusion Layers on Ice Crystallization in Polymer Electrolyte Fuel Cells

The unassisted cold-start capability of polymer electrolyte fuel cells (PEFCs) remains challenging for large-scale automotive applications. Various studies have shown that the freezing of produced water at the cathode catalyst layer (CL) and gas diffusion layer (GDL) interface blocks the oxidant gas and leads to a cold-start failure. However, the impact of GDL properties, including substrate, size, and hydrophobicity, on the freezing behavior of supercooled water is yet to be thoroughly investigated. We use differential scanning calorimetry to perform non-isothermal calorimetric measurements on untreated and waterproofed GDLs (Toray TGP-H-060, Freudenberg H23). By conducting a large number of experiments (>100) for each type of GDL, we obtained the corresponding distribution of onset freezing temperature (T_onset) and found noticeable sample-to-sample variations in both untreated and waterproofed GDLs. Furthermore, ice crystallization is affected by GDL wettability, coating load, coating distribution, and GDL size, whereas the impact of the GDL substrate and saturation level is not apparent. The T_onset distribution allows for predicting the capability of PEFC freeze-start and the freezing probability of residual water at a given subzero temperature. Our work paves the way for GDL modifications toward the improved cold-start capability of PEFC by identifying and avoiding the features that systematically trigger the freezing of supercooled water with high probability.