Capillary Hysteresis in Neutrally Wettable Fibrous Media: A Pore Network Study of a Fuel Cell Electrode

Abstract

Hysteresis in the saturation versus capillary pressure curves of neutrally wettable fibrous media was simulated with a random pore network model using a Voronoi diagram approach. The network was calibrated to fit experimental air-water capillary pressure data collected for carbon fibre paper commonly used as a gas diffusion layer in fuel cells. These materials exhibit unusually strong capillary hysteresis, to the extent that water injection and withdrawal occur at positive and negative capillary pressures, respectively. Without the need to invoke contact angle hysteresis, this capillary behaviour is re-produced when using a porescale model based on the curvature of a meniscus passing through the centre of a toroid. The classic Washburn relation was shown to produce erroneous results, and its use is not recommended when modelling fibrous media. The important effect of saturation distribution on the effective diffusivity of the medium was also investigated for both water injection and withdrawal cases. The findings have bearing on the understanding of both capillarity in fibrous media and fuel cell design.

Investigating Electrode Flooding in a Flowing Electrolyte, Gas‐Fed Carbon Dioxide Electrolyzer

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Alkaline Water Electrolysis at 25 A cm−2 with a Microfibrous Flow‐through Electrode

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Electrospinning as a route to advanced carbon fibre materials for selected low-temperature electrochemical devices: A review

“…Over the last several years, researchers have begun to investigate whether smaller fibres might be better suited for GDLs, and electrospinning is the ideal platform from which to launch such studies. For a given porosity, smaller fibres mean smaller pores, and the curved nature of the fibre surfaces impact the capillary behaviour via the Purcell effect [166], so smaller fibres also exhibit increased hydrophobicity [167]. Since one of the main roles of GDLs is water management, it follows that GDLs with smaller hydrophobic fibres would be less prone to water flooding, resulting in lower overall water saturations.…”