Liquid-Water-Droplet Adhesion-Force Measurements on Fresh and Aged Fuel-Cell Gas-Diffusion Layers
Optimal water management in proton-exchange-membrane fuel cells at lower temperatures requires the efficient removal of liquid water from the cell. This pathway is intimately linked with liquid-water-droplet removal from the surface of the gas-diffusion layer (GDL) and into the flow channel. In this study, these liquid-water phenomena are investigated experimentally to improve the understanding of water transport through, and removal from, the GDL. Specifically, an experiment using a sliding-angle measurement is designed and used to quantify and measure directly the adhesion force for liquid-water droplets and to understand the droplets' growth and detachment from the GDL. The results show that unlike the static contact angle, the adhesion force, as measured by sliding angles, provides a good indicator of water-droplet removal as it is a direct measure of the dominating force that is holding a droplet on the GDL surface and preventing its detachment. It is also observed that injection through the GDL, as is representative of operating fuel cells, results in a higher adhesion force than a droplet placed on the top surface. Finally, it is shown that aged GDLs demonstrate higher adhesion forces, which dominate GDL degradation response and fuel-cell water holdup.