Hydrophilic and Hydrophobic Composite Microporous Layer Coated Gas Diffusion Layers for Performance Enhancement of Polymer Electrolyte Fuel Cells

Abstract

A novel microporous layer (MPL) coated gas diffusion layer (GDL) is developed to improve water management of polymer electrolyte fuel cells (PEFCs) by incorporating hydrophobic and hydrophilic pores within the same layer. This MPL expels excess water at the interface between the catalyst layer and MPL through hydrophilic pores while maintaining efficient oxygen transport through hydrophobic pores, reducing oxygen transport resistance under high humidity conditions. The water permeability and relative oxygen permeance tests demonstrate the presence of separate hydrophobic and hydrophilic pores in the appropriate composite MPL. The effects of combinations of hydrophilic and hydrophobic binders used in the composite MPLs on the oxygen transport resistance are evaluated. The hydrophobic polytetrafluoroethylene (PTFE) binder and the hydrophilic polyvinyl alcohol (PVA) binder cannot enhance performance due to mismatched sintering temperatures. Although the hydrophobic polyvinylidene fluoride (PVDF) and PVA binders have the same sintering temperature, the performance was degraded due to the strong hydrophilicity of PVA. Another combination of composite MPL incorporates hydrophobic PVDF and Nafion binders. Hydrophilic TiO2 particles are introduced in the Nafion binder to reinforce the hydrophilicity. The appropriate composite MPL significantly reduced the total oxygen transport resistance compared to those obtained with the hydrophobic MPL.