Steam Effect on Cell Performance

The positive effect of water on the fuel cell performance was further proven by introducing several H2O/H2 mixtures into the anode compartment. I-V curves were recorded for each water vapor partial pressure as shown in Fig. 22. I-V curves were recorded fast, within a time interval less than 30 s, so that the water produced at the cathode would not equilibrate with the membrane. It is evident in Fig. 22 that by increasing the water partial pressure a threefold increase of the cell performance is observ ed, thus proving the vital importance of steam for the efficient operation of the phosphoric acid imbibed high temperature MEA. 

Though water vapor plays a significant role in the fuel cell performance, the humidification of H2 and O2 is not necessary under fuel cell operating conditions. The water vapors produced at the cathode compartment are enough for the humidification of the membrane by the back-transport process from the cathode to the anode compartment of the cell (Fig. 21), thus affecting the ionic conductivity of the membrane electrolyte and, as shown below, on the polarization of the electrode/electrolyte interfaces. 

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