A New Water Saturation Jump Model at Gdl/MPL/CL Interfaces of a PEM Fuel Cell
In the present work, we propose a new approach to study the interfacial water behavior at the GDL/MPL/CL interfaces in a PEM fuel cell. Porosimetric measurements and SEM images show the mean pore size in GDL about 20-40 times larger than in MPL, and the pore size in MPL about 10-20 times larger than in CL . As for such large pore size difference, it is safe to assume that the MPL pores are sufficient small and the GDL pores are infinitely open at the GDL/MPL interface, as well as MPL/CL interface. In Fig.2, cubic pores and sphere packing pores are assumed in GDL and MPL, respectively. The relationship between water coverage on MPL (CL) surface and water saturation in GDL (MPL) interfacial pore is obtained by geometric analysis. In addition, pores in GDL and MPL have mixed wettability. For simplicity, we further assume that the water droplet will not be influenced by the sidewalls in hydrophobic pores (as shown in Fig.2) and will completely adhere to the sidewalls in hydrophilic pores. As a result, a macroscopic relationship between the water coverage sc on finer layer surface and water saturation sint,p in interfacial pores in coarse layer is obtained as a function of hydrophilic pore fraction x,
The expression of the function f(sint,p)for hydrophobic pores can be found in Fig.2. Fig.3 shows the relationship curves of the interfacial saturation at the GDL/MPL and MPL/CL interfaces with two different contact angles of finer layer surface. This new proposed interfacial model predicts more reasonable water distribution at the GDL/MPL/CL interfaces, and is used in multiphase mixture model of PEM fuel cells to study the water transport and mass transfer limitation in several cases.
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