A new cross-sectional visualization cell in which a transparent material is not embedded in the separator was developed to observe water droplet behavior in a flow channel and to analyze the impact of the channel and gas diffusion layer (GDL) surface on the behavior. A specific GDL and separator pair was chosen so that the surface of the GDL was more hydrophobic than that of the separator, where the contact angle difference between them was approximately 27°. With this GDL and separator pair, a droplet formed in the channel does not touch the GDL surface. This specific pair also makes the droplet smaller and causes less of a pressure drop through the channel, leading to superior drainage from the channel. A theoretical analysis based on the force balance surrounding a droplet explains this superior drainage. The reason is that the combination of the hydrophobic GDL and hydrophilic separator reduces the adhesion force on the droplet, promoting water drainage.
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