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Effect of freeze/thaw cycles on the performance of polymer electrolyte membrane fuel cell (PEMFC) is investigated. Freeze/thaw cycle is repeated 40 times. The performance is degraded, as the number of freeze/thaw cycles increases. The maximum degradation is about 35% at high current density. The performance degradation is analyzed based on the change of water distribution. X‐ray visualization is conducted 3 times; before, after 10th and 40th freeze/thaw cycle, respectivly. The water saturation in PEMFC is getting reduced, as the number of freeze/thaw cycles increases. Over‐potential analysis is conducted using visualization result by calculating the proton conductivity. The proton conductivity is decreased about 30% at high current density after 40th freeze/thaw cycle. The change of water distribution is analyzed based on the structural change of the GDL. The water volume change upon freeze/thaw cycle leads to cracks in the micro porous layer. It facilitates water removal from the GDL and leads to low water saturation in PEMFC.

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