Experimental study on the influence of operating conditions on performance decline with periodic anode purges in a vehicular PEMFC stack

Abstract

Periodic anode purges can remove excessive liquid water and nitrogen in the anode to mitigate hydrogen starvation in PEMFCs caused by flooding and nitrogen buildup. Experiments were conducted on a vehicular PEMFC stack to evaluate influences of operating conditions including current density, cathode flowrate, hydrogen recirculation and working pressures on performance decline during operations with anode purges. The accumulation of anode impurities was characterized by voltage decrease, voltage uniformity and anode pressure swing. The results reveal that anode flooding develops greatly with increasing current density. An optimal hydrogen recirculation pump speed of 1000 rpm substantially improves voltage stability and uniformity of the stack. High cathode pressure accelerates the impurity accumulation in the anode, while high anode pressure facilitates the removal of nitrogen. When the stack works with a constant pressure difference of 10–20 kPa between two electrodes, nitrogen buildup in the anode can be minimized and flooding becomes the primary contributor to performance decline under automotive operating conditions. As current density rises to 300–700 mA/cm2, the optimal pressure difference increases from 10.2 to 14.7 kPa.