Liquid-Water Interactions with Gas-Diffusion-Layer Surfaces

Understanding dynamic liquid-water uptake and removal in gas-diffusion layers (GDLs) is essential to improve the performance of polymer-electrolyte fuel cells and related electrochemical technologies. In this work, GDL properties such as breakthrough pressure, droplet adhesion force, and detachment velocity are measured experimentally for commonly used GDLs under a host of test conditions. Specifically, the effects of GDL hydrophobic (PTFE) content, thickness, and water-injection area and rate were studied to identify trends that may be beneficial to the design of liquid-water management strategies and next-generation GDL materials. The results conclude that liquid water moving transversely through or forming at the surface of GDL may be affected by internal capillary structure. Adhesion-force measurements using a bottom-injection method were found to be sensitive to PTFE loading, GDL thickness, and injection area/rate, the latter of which is critical for defining the control-volume limits for modeling and analysis. It was observed that higher PTFE loadings, increased thickness, and smaller injection areas led to elevated breakthrough pressure; meaning there was a greater resistance to forming droplets. The data are used to predict the onset of droplet instability via a simple force-balance model with general trend agreement. (C) The Author(s) 2014. Published by ECS. This is an open access article distributed under the terms of the Creative Commons Attribution 4.0 License (CC BY, http://creativecommons.org/licenses/by/4.0/), which permits unrestricted reuse of the work in any medium, provided the original work is properly cited. All rights reserved.