Hydrophilic and hydrophobic double microporous layer coated gas diffusion layer for enhancing performance of polymer electrolyte fuel cells under no-humidification at the cathode

Abstract

Gas diffusion layers (GDLs) coated with a hydrophobic microporous layer (MPL) have been commonly used to improve the water management properties of polymer electrolyte fuel cells (PEFCs). In the present study, a new hydrophilic and hydrophobic double MPL coated GDL was developed to achieve further enhancement of PEFC performance under no-humidification at the cathode. The hydrophobic MPL, which consists of carbon black and polytetrafluoroethylene (PTFE), was coated on the carbon paper substrate. The hydrophilic layer, which consists of carbon black and polyvinyl alcohol (PVA), was also coated on the hydrophobic MPL. The hydrophilic layer is effective for conserving humidity at the catalyst layer, while the hydrophobic intermediate layer between the hydrophilic layer and the substrate prevents the removal of water in the hydrophilic layer via dry air in the substrate. Both decrease in the hydrophilic layer thickness to 5 μm and appropriate enhancement of hydrophilicity by increasing the PVA content to 5 mass% are effective for enhancing PEFC performance. Reducing the maximum pore diameter of hydrophobic intermediate layer to 20 μm is also effective for enhancing PEFC performance. However, when the pore diameter of the hydrophobic layer becomes too small, concentration overpotential tends to increase, thereby lowering PEFC performance.