MODELING AND EXPERIMENTS OF VOLTAGE TRANSIENTS OF PEM FUEL CELLS WITH THE DEAD-ENDED ANODE

摘要

The operation of PEM fuel cells (PEMFC) with dead-ended anode (DEA) leads to severe voltage transients due to accumulation of nitrogen, water vapor and liquid water in the anode channels and the gas diffusion layer (GDL). Accumulation of nitrogen causes a large voltage transient with a characteristic profile whereas the amount of water vapor in the anode is limited by the saturation pressure, and the liquid water takes up very small volume at the bottom of the anode channels in the case of downward orientation of the gravity. Here, we present a transient ID along-the-channel model of PEMFCs operating with periodically-purged DEA channels. In the model, transport of species is modeled by the Maxwell-Stefan equations coupled with constraint equations for the cell voltage. A simple resistance model is used for the membrane to express the permeance of nitrogen and transport of water through the membrane. The model results agree very well with experimental results for the voltage transients of the PEMFC operating with DEA. In order to emphasize the effect of nitrogen accumulation in the anode, we present experimentally obtained cell voltage measurements during DEA transients, when the cathode is supplied with pure oxygen. In the absence of nitrogen in the cathode, voltage remained almost constant throughout the transient. Then, the model is used to determine the effect of oxygen-to-nitrogen feed ratio in the cathode on the voltage transient behavior for different load currents. Lastly, the model is used to show the effect of the small amount of leak from the anode exit on the voltage transient; even for leak rates as low as less than 10 ml/h, nitrogen accumulation in the anode channels is alleviated and the cell voltage remained almost constant throughout the transient.