Influences of microporous layer design parameters for gas diffusion layer on permeability and PEFC performance

Gas diffusion layers (GDLs) coated with a microporous layer (MPL) have been commonly used to improve water management properties of polymer electrolyte fuel cells (PEFCs). However, the appropriate pore diameter, thickness and hydrophobicity of the MPL remain unclear. In the present study, the influences of MPL design parameters on permeability and PEFC performance were evaluated. A decrease in the pore diameter of the MPL reduces through-plane permeability significantly, but reduces in-plane permeability only slightly. Under high-humidity conditions, a decrease in the MPL pore diameter is effective for preventing flooding, enhancing the PEFC performance. However, when the pore diameter becomes too small, the PEFC performance tends to decrease. Reducing the MPL thickness improves in-plane permeability, enhancing the ability of the MPL to avoid flooding. Under low-humidity conditions, a decrease in the MPL pore diameter is effective for preventing drying-out of the MEA. Increasing the MPL thickness is also effective for maintaining the humidity of the MEA. However, when the MPL thickness becomes too large, the transport of oxygen to the electrode through the GDL is deteriorated, lowering the PEFC performance.