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PEM Fuel Cells by Ken S. Chen, Yun Wang

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7.4 STATE OF SUBFREEZING WATER

The state of subfreezing water inside the pores of catalyst layers significantly affects freezing operation, specifically, the reduction in reaction surface coverage and increase in oxygen transport resistance caused by product water. For example, the ice crystal shape determines the contacting area between the reaction surface and ice. Supercooled water may be present in PEM fuel cells and able to move out of the cathode electrode and into the MPL, GDL, and even gas flow channels. Figure 7-19 shows an experimental visualization of product water on the catalyst layer surface, along with the evolution of cell voltage. The MEA was cooled to −10°C using a Peltier element and the voltage was fixed at 0.5 V. In the ...

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