Experimental and numerical comparison of water transport in untreated and treated diffusion layers of proton exchange membrane (PEM) fuel cells

Shahraeeni, Mehdi; Hoorfar, Mina

doi:10.1016/j.jpowsour.2013.03.023

Cited by 11 publications

(3 citation statements)

References 74 publications

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“…The higher breakthrough pressure at elevated PTFE loadings may be amplified by the heterogeneous distribution of PTFE that can reduce the number of pores available to water invasion. 40,41 Figure 7a shows the results of breakthrough pressure as a function of GDL sample thickness which agree with trends reported in literature. 34 A higher breakthrough pressure is expected as increased GDL thickness, l, usually means longer flow pathways and an increased number of pores liquid water must fill before reaching the surface.…”

Section: Resultssupporting

confidence: 89%

“…Several theories exist as to the mechanism of liquid-water transport through the GDL and how a droplet forms on the GDL surface. 8,19,20,40 For example, Nam and Kaviany 19 proposed an upside-down capillarytree network using a theoretical approach. Later, Litster et al 8 showed experimentally that fingering and channeling are dominant scenarios and an upside-down capillary-tree network is less reasonable for PEFC GDLs.…”

Section: Discussionmentioning

confidence: 99%

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Liquid-Water Interactions with Gas-Diffusion-Layer Surfaces

Santamaria

Das

MacDonald

et al. 2014

J. Electrochem. Soc.

114

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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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Section: Resultssupporting

confidence: 89%

Section: Discussionmentioning

confidence: 99%

Liquid-Water Interactions with Gas-Diffusion-Layer Surfaces

Santamaria

Das

MacDonald

et al. 2014

J. Electrochem. Soc.

114

View full text Add to dashboard Cite

show abstract

“…Thus, pore-network models (PNMs) [12][13][14][15][16][17][18] have been adopted to investigate microscale liquid water transport inside hydrophobic PTLs. These studies have shown that invasion-percolation with active capillary 100 fingering is an important transport mechanism.…”

Section: Introductionmentioning

confidence: 99%