Microporous layer-coated gas diffusion layer to reduce oxygen transport resistance in a polymer electrolyte fuel cell under high humidity conditions

A hydrophilic and hydrophobic microporous layer (MPL)-coated gas diffusion layer (GDL) is developed to enhance the performance of polymer electrolyte fuel cells (PEFCs) under high humidity conditions. The oxygen transport resistance is determined from the limiting current density value of polarization curves as a means of evaluating the ability of the GDL to prevent flooding. A double MPL coated GDL, in which a thin hydrophilic layer is coated on the hydrophobic MPL, is effective at expelling excess water from the catalyst layer, thus reducing the oxygen transport resistance. The PEFC performance is highly dependent on the hydrophobic MPL in the double MPL. Appropriate enhancement of the hydrophobicity, obtained when incorporating 20 mass% polytetrafluoroethylene (PTFE) in the MPL, is essential for reducing the oxygen transport resistance. A triple MPL-coated GDL, in which the PTFE content in the hydrophobic MPL in contact with the hydrophilic layer is 20 mass% and that in contact with the carbon paper substrate is 10 mass%, exhibits much lower oxygen transport resistance than a conventional hydrophobic MPL-coated GDL.