Water management in cathode channel of polymer electrolyte fuel cell (PEFC) is essential for achieving high current density operation, because excessive liquid water generated at cathode clogs gas channel and disturbs air flow. This phenomenon known as “channel plugging” is one of the critical issues for high-performance PEFC. In this study, the liquid water behavior in the cathode flow channel of an operating PEFC was directly visualized through the transparent separator using a high-speed camera. Furthermore, the differential pressure between the inlet and outlet of the cathode channel was quantitatively measured to predict the liquid water accumulation, and the effects of wettability (hydrophilic or hydrophobic) and flow direction (vertical or horizontal) of the cathode channel on the plugging phenomena were investigated. It was found that the hydrophobic treatment of the cathode channel is effective in draining liquid water smoothly and reduces the averaged differential pressure. The fluctuation of the differential pressure tends to be large due to the sufficient water removal. On the other hand, in the case of hydrophilic treatment, much water attaches to the channel wall and remains inside the gas channel. In addition, the liquid water transport within the cathode channel is largely affected by the flow direction. The averaged differential pressure in the horizontal flow is much lower than that in the vertical flow. The horizontal flow has the advantage of discharging much water to the outside of the cell because the gravity effect can be neglected.

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