Separation of water and oxygen pathways in microporous layer coated gas diffusion layers to reduce oxygen transport resistance of polymer electrolyte fuel cells

Reducing the oxygen transport resistance is essential for enhanced performance of polymer electrolyte fuel cells (PEFCs) operating at high current densities. Increasing the porosity of the microporous layer (MPL) coated gas diffusion layer (GDL) is effective for reducing the oxygen transport resistance. The premixed method, in which pore former (PF) particles are directly added to a hydrophobic MPL slurry, is commonly used to increase the MPL porosity. However, the appropriate PF-MPL preparation method, PF content, and wettability are not clarified. In the present study, a novel preparation method, in which a PF slurry and a hydrophobic slurry are separately mixed, is developed to independently generate large pores for water pathways and small pores for oxygen transport pathways. These controlled pore structures result in lower oxygen transport resistance than premixed PF-MPLs. Adding hydrophilic TiO 2 particles to the PF slurry reduces the water breakthrough pressure, which enhances the water removal ability through the large pores and further reduces the pressure-independent oxygen transport resistance. Adding small-sized PF particles to the hydrophobic slurry increases the porosity of the small pores. This reduces the pressure-dependent oxygen transport resistance, resulting in a further reduction in the oxygen transport resistance.