Effect of Hydrophobic Polymer Treatments on the Capillary Properties of Gas Diffusion Layers for Polymer Electrolyte Membrane Fuel Cells

摘要

Increasing the current density of polymer electrolyte membrane fuel cells (PEMFC) leads to reduced stack size and materials cost, both of which are necessary if fuel cells are to become commercialized. Increasing current density, however, also means increased production of water inside the cell. The presence of liquid water in the porous electrode layers, particularly the gas diffusion layer (GDL), dramatically reduces the flux of gaseous reactants to the catalyst sites by blocking pores, thereby imposing mass transfer limitations on the maximum current that can be attained in a cell (1). To mitigate the negative effect of liquid water, a hydrophobic coating is usually applied to the GDL to alter its capillary properties. Although this approach is known to improve cell performance under high current density operation, the actual change in the GDL capillary properties is unclear since reliable experiments have not been available. In this paper, a recently developed method for measuring water-air-GDL capillary pressure curves (2) is applied to GDLs with varying amounts of PTFE coatings to quantitatively determine changes in water behavior. Access to such direct information about the capillary properties of GDLs will allow coating procedures to optimized and tailored to provide the desired water behavior in the cell.