Special Features of PEMFC Operation

3 SPECIAL FEATURES OF PEMFC OPERATION 3.3.1 Water Management 

In PEMFC operation, water is formed as a reaction product at the positive (oxygen) electrode. It can be seen from reaction (3.2a) that water reaches the side of 

To avoid these situations, the hydrogen that is supplied is usually saturated with water vapor, and the oxygen is circulated. Passing next to the electrode, the oxygen becomes saturated with water vapor. It then reaches a chamber with a lower temperature, where the water vapor condenses, and dry oxygen is returned to the electrodes. Sometimes, the periodic release of excess oxygen saturated with water vapor is practiced. The liquid water that is produced may be used for other purposes, such as drinking water. 

All these processes must be controlled quite carefully. If water withdrawal is too fast, there is a risk of water loss from the swollen membrane, which not only leads to a drastic rise in resistance but also to fragilization. Cracks may then develop across which the gases may mix, yielding an explosive mixture, with all the catastrophic consequences that ensue. 

A large problem in PEMFC operation is a possible partial condensation of water vapor when temperature gradients are present in the fuel cell, and a dualphase water system develops. The liquid water forming within the MEA or in the channels of the bipolar plates interferes with the access of reactant gases to the catalytically active layer, thus causing additional polarization of the electrodes and a drop in the cell s discharge voltage. 

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