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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. • An optimal recirculation rate greatly improves voltage stability and uniformity. • Anode nitrogen buildup can be minimized with a constant pressure difference. • The optimal pressure difference rises with the increase of current density. • Pressure swing at anode inlet reflects flooding development in the anode. [ABSTRACT FROM AUTHOR]

For analyzing ejector's performance in the system, an ejector for a 10 kW polymer electrolyte membrane fuel cell (PEMFC) system was first designed, manufactured, and a 10 kW PEMFC system bench was built up. A proportional valve and PI pressure feedback control method were adopted to control the hydrogen supply and anode inlet pressure. During the test, performances between dead-ended anode (DEA) mode and ejector mode were compared. Ejector's performances in the system, i.e., volume flow recirculated ratio, difference pressure, dynamic responses of primary pressure, anode inlet pressure, and recirculated gas flow rate during the purge process and current variation condition, were investigated. The results show that pressure adjustment is accurate, continuous, and fast using the proportional valve and PI pressure feedback control method. The hydrogen consumption rate in the ejector mode can reduce from 5% to 10% compared with the rate in the DEA mode except for the stack current 5 A and 10 A conditions. For better water removal out of the anode channel in ejector mode, the maximum stack power increases from 5.11 kW (DEA mode) to 9.56 kW (ejector mode). Anode pressure surge caused by the purge valve switching enhances the ejector's recirculated performance significantly. • An ejector for a 10 kW PEMFC system is designed, manufactured and evaluated. • The stack in ejector's mode shows a better performance than that in DEA mode. • Hydrogen recirculation can reduce the hydrogen consumption. • The proportional valve with the PI pressure feedback method can accurately control the anode inlet pressure. • Anode pressure surge can enhance ejector's recirculated performance. [ABSTRACT FROM AUTHOR]

Distributions of water and oxygen concentration are the two main factors that influence the consistency of current density in a polymer electrolyte membrane fuel cell. While the former type is relevant to the ohmic loss, the latter one associated with the mass transfer loss. In a self-humidified condition, higher demand for water management is requested as membrane drying often appears. To investigate the effects of flow pattern and hydrogen recirculation on the consistency of current density, the cell is tested under five different conditions, and a quasi-three-dimensional transient non-isothermal model is developed to explain different experimental phenomena in this study. Differences of distributions of current density, resistance and reaction gases are examined by comparing co-flow with counter-flow conditions, humidified with self-humidified conditions and dead-ended anode with hydrogen recirculation conditions. The results show that consistency reduces with the cell current density increasing, and gas humification is significantly beneficial. In co-flow configurations, the standard deviation of local current density increases from 0.02 at 0.2 A cm−2 to 0.14 at 1.2 A cm−2 under the humidified condition, increasing from 0.38 at 0.2 A cm−2 to 0.26 at 1.2 A cm−2 under the self-humidified condition. The water distribution of the cell in counter-flow configuration is more uniform than that in the co-flow configuration under the whole current density conditions. Hydrogen recirculation can improve the water content of segments near the inlet gas channel in the anode, and the consistency is the best when the current density is larger than 0.4 A cm−2. • A segmented single cell model is developed. • It has a higher demand for water management in a self-humidified condition. • Consistency in counter-flow configuration is better than that in co-flow way. • Recycled vapor in anode can improve consistency of local current density. [ABSTRACT FROM AUTHOR]