Mechanisms of voltage spikes and mitigation strategies for proton exchange membrane fuel cells with dead-ended anode under pressure swing operation

摘要

In proton exchange membrane fuel cells with dead-ended anode, water and nitrogen can accumulate in the anode, causing cell performance decrease and cell degradation. The anode pressure swing operation can reduce the local accumulation of water and nitrogen by generating an oscillatory flow in the anode channel. However, sharp spikes are observed in cell voltage and these spikes are especially large near the end of a purge period. Thus the mechanisms of these voltage spikes are studied through dynamic voltage and local current measurements. The measurement results show that even though the average current density is maintained constant, local current densities also experience sharp spikes and these spikes occur at exactly the same time as the voltage spikes. By examining the spikes in local current densities, it is found that in the upstream the spikes are upward and in the downstream downward. Further detailed study show that the periodical spikes of cell voltage and local current densities are due to the backflow of liquid water and nitrogen in the anode channel from the outlet tube. Based on the mechanism, a novel approach to alleviate the cell voltage spikes is proposed adding an anode exit reservoir. The experimental results with the anode exit reservoir show that it is very effective in reducing the spikes of cell voltage and local current densities by storing accumulated liquid water and nitrogen and enhancing the backflow of hydrogen. With the anode exit reservoir, the effect of the pressure pulsation amplitude on the cell performance is also studied. The experimental results show that there is a threshold of the pressure pulsation amplitude for a specific fuel cell system and the threshold for the experimental fuel cell is around 0.05 bar. (C) 2017 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.