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. Polymer-electrolyte fuel-cell (PEFC) and redox flow-battery (RFB) systems have the potential to improve energy efficiency and storage capabilities for mobile and grid-level applications in the near future. In PEFCs, the electrode structure is composed of a catalytic layer supported by porous gas-diffusion layers (GDLs) where multiphase reactant/product transport and electron conduction occur. Product liquid water can contribute to performance and degradation issues if not properly handled. Numerous studies have shown the importance of water-management strategies during start-up/shutdown and cooler operation where lower cell temperatures may lead to liquid buildup. [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15] In RFBs, GDLs serve a similar purpose of effective reactant distribution, especially for gaseous cells, 16,17 as well as serving as possible catalysts.18 Understanding multiphase, dynamic GDL water uptake and removal is essential to develop effective liquid-water management schemes as well as next-generation GDL materials for improved PEFC and RFB performance, stability, and component lifetimes.The influence of the porous-electrode structure on liquid/gas transport and PEFC performance has been studied by several groups focusing on the role of GDL and microporous layer (MPL) effects. [19][20][21][22] Capillary and viscous forces govern two-phase flow through GDLs; the dimensionless parameters that quantify them are the capillary number and viscosity ratio defined asandrespectively, where u is the superficial velocity of the non-wetting phase, γ is the surface tension, and μ is the wetting (wet) and nonwetting (nw) phase viscosities. 10,23 Under normal PEFC operation, capillary fo...

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High-power electrodes in electrochemical technologies (e.g., fuel cells) typically require ultra-thin catalyst layers, which, especially when multiphase flow exists, exhibit mass-transport limitations. These have been mitigated through new backing layer structures and nontraditional removal of water out of the anode side of the cell for a new design and operation paradigm.

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