Experimental Investigation of Aging for Multi-Segments PEM Fuel Cell With Dynamic Loading Cycles

Abstract

The effect of humidification on aging of local membrane electrode assembly (MEA) was investigated using dynamic cycling-change output current measurements. During the investigation, the active area of MEA was divided into 8 segments from upstream to downstream. The experiment was carried out before activation and those results served as bench mark for the results obtained after activation. The results of humidification of MEA were collected from the high frequency resistance (HFR). It was found that HFR of the first region was largest due to less water humidification. With the gas flow to the downstream, the concentration of vapor and liquid water was high, the MEA was humidified and consequently the value of HFR also decreased. The flooding in the last segment was might be due to the accumulation of water. This phenomenon resulted in the undershoot of HFR curve. The HFR curve would become steady when the flooding was removed at the last segment. The experiment of dynamic output current was carried out for 450 cycles and the total time was about 150 hours. It was found that the polarization curve became steady had less differentiation between each segment after 450 cycles of dynamic output current measurements tests. The slop of cyclic voltammetry (CV) curves charts increased from region 6 to region 8. It was supposed that the water content in the MEA was less at low loading condition and the MEA become dried. But the water content was more in high loading condition. The MEA would be in the cycle of expansion and contraction during the drying and humidification exchange process. The result suggested that the membrane might be affected easily in the downstream. Besides, the surface area of catalyst would also decay the peak of CV curve due to the water flooding which might block the mass transfer resulting in fuel starvation, carbon corrosion and catalyst degradation in downstream.