Water balance in a free-breathing polymer electrolyte membrane fuel cell

Water balance in a free-breathing polymer electrolyte membrane fuel cell was studied, focusing on the effect of anode conditions. The methods used were current distribution measurement, water collection from the anode outlet, and the measurement of cell polarization and resistance. Current density levels were 100 and 200 mA cm−2, temperature levels were 40 and 60 °C, and hydrogen stoichiometry range was from 1.5 to 2.5. The direction of hydrogen flow was varied. The fraction of product water exiting through the anode outlet varied from 0 to 58%, and it was found to increase with increasing temperature and hydrogen flow rate. When the general direction of hydrogen flow was against the direction of air flow, the percentage of water removal through the anode was smaller and the current distributions were more even than in the cases where the direction was the same as that of the air flow. This probably resulted from a more favorable distribution of water over the active area. The results also indicate that the net water transport coefficient varies across the active area. In further measurements, operation with the anode side in dead-end mode was investigated. It was also found that water distribution was more favorable when the general direction of hydrogen flow was against the air flow.