engleski

Tracking the process at PEM fuel cell cathode in h-x diagram

It is possible to select the Proton Exchange Membrane (PEM) fuel cell operating conditions, i.e., temperature, pressure and flow rates, such that the product water is just sufficient to saturate the cathode exhaust without external humidification of air at the cathode inlet. Such operation would not be advisable in isothermal conditions because the air would heat up immediately after entering the cathode compartment and the product water would not be sufficient to humidify it until the very exit. However, it is possible to impose such a temperature gradient on the cathode flow field that would allow air to slowly heat up in such a manner that product water evaporates and maintains close to 100% relative humidity (RH) throughout the length of the cathode channel. In order to prove this concept, a segmented fuel cell has been designed, allowing each segment to be held at a desired previously calculated temperature. Humidity sensors were incorporated between the segments so that the process can be monitored. The segmented fuel cell was operated in both isothermal and variable temperature modes. The temperature and humidity content of the air along the cathode channel for both modes can be shown in h-x diagram, from which it is possible to conclude on the efficiency of this internal humidification process. As expected, operation in variable temperature mode resulted in better performance than the isothermal operation, due to maintaining close to 100% RH over almost the entire length of the anode and cathode channel. This results in a simplified supporting system without the necessity for external humidification of reactant gases.

Fuel cell, operating conditions, relative humidity of reactant gases, cathode channel, variable temperature flow field, isothermal conditions, .

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