We wish to understand the autonomou

We wish to understand the autonomous operation of the PEM fuel cell; operation of the fuel cell under galvanostatic or potentiostatic control can distort the autonomous dynamics. The feed flow was also fixed and was not slaved to the current as is frequently done in fuel cell operation. Most experiments were carried out with a hydrogen flow rate of10 cm3/ min, which limited the current to ∼680 mA. In most instances the currents in our experiments were < 200 mA. In the results presented here we have limited ourselves toconditions where liquid water is not present in the fuel cell (relative humidity is kept below 100%). When liquid water condensed in the fuel cell, it operated irregularly. The gas flow would change erratically due to water droplets blocking the effluent. The irregular operation of the PEM fuel cell with liquid water formation is highly relevant to the fuel cell pathology, but it lies beyond the scope of this paper.