Effect of Liquid Water Saturation on Oxygen Transport in Gas Diffusion Layers of Polymer Electrolyte Fuel Cells

Improved oxygen diffusivity is essential for reducing mass transport losses in polymer electrolyte fuel cells (PEFCs). In this work, effective oxygen diffusivity in the presence of liquid water inside a gas diffusion layer (GDL) was investigated by means of coupled experimental and numerical analyses. In order to control the liquid water content inside the GDL, a temperature gradient method was developed. In a separate experiment liquid water content inside the GDL was measured by neutron radiography (NR) and analyzed by using a two-phase, non-isothermal numerical model. The model accurately reproduced the total liquid water content and was in qualitative agreement with the liquid saturation trend as obtained from the NR experiments, which was utilized to estimate the liquid saturation in the limiting current experiment. Based on the predicted liquid water profile, the dependence of effective oxygen diffusivity on the liquid water saturation is deduced. It is found that the Bruggeman exponent factor is much larger than the predictions from network models and this suggests that the understanding of the relationship between liquid water transport and the GDL local structure is important.