Optimal PTFE content in micro porous Layer on Cathode of Polymer Electrolyte Membrane Fuel Cell with Different GDM Types

摘要

This work is to study the effects of the polytetrafluoroethylene (PTFE) content in micro porous layer (MPL) and the type of gas diffusion medium (GDM) on cathode performance in a polymer electrolyte membrane fuel cell (PEMFC). Generally, gas diffusion layers (GDLs) for PEMFC are constructed double layers of GDM and MPL. The MPL which consist of carbon powder and PTFE can enhance the ability of water management. PTFE content in MPL increases hydrophobicity of MPL and prevents cathode water flooding. An excess PTFE content in MPL, indicating the MPL with a quit small pore size, causes poor diffusion of fuel gas in the gas diffusion layer (GDL). By contrast, if the content is too low, the water generated in the cell cannot be effectively removed. In this work, various PTFE contents from 10 to 40 wt.% were tested to obtain optimal PTFE content and the effect of GDM type was also investigated using felt type and paper type which have same thickness. MPL slurry was prepared by homogeneous blending of carbon powder (Vulcan XC-72R), PTFE suspension (DuPont), isopropyl alcohol and glycerol. Then the slurry was coated on GDM surface with controlled thickness by Doctor Blade casting method. The prepared GDLs were measured by surface morphology, porosity, gas permeability and electrical resistance. Moreover, the GDLs were tested in a 25 cm~2 single cell at 75 °C in humidified H2/air condition. As a result, different optimal PTFE contents were obtained from GDMs with different types. Therefore, the optimal PTFE content depends on the GDM type. Consequently, the determination of appropriate PTFE content in MPL and GDM type is the critical factor for cathode performance in a PEMFC.