科研之友
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摘要
The durability of proton exchange membrane (PEM) fuel cells is a key factor which prevents its commercial application on the vehicle. Dynamic current cycle is one of the most common conditions for PEM fuel cells, especially varying the currents between the idling and the rated condition. To investigate the degradation behavior of fuel cells under this kind of dynamic cycles, a PEM fuel cell stack with 330 cm(2) active area is operated under 10,000 dynamic cycles with the cycling current density ranging from 25 mAcm(-2) to 600 mAcm(-2), which simulates common operating conditions in a vehicle cycle from the idling condition to the rated condition. Polarization curves, the high-frequency resistance (HFR), the uniformity of the individual cells, the performance degradation of PEM fuel cell stack at 25 mAcm(-2) and 600 mAcm(-2) are characterized to investigate the performance degradation over cycling. In addition, scanning electron microscopy (SEM) of the surface and the cross-section of the tested membrane electrode assemblies (MEAs) are compared with different single-cell samples. The results indicate that the degradation rate of the stack is 1.0 mu Vcycle(-1) at 25 mAcm(-2) under the idling condition. A more severe performance degradation of about 2.0 mu Vcycle(-1) is detected at 600 mAcm(-2) under the rated condition. The individual cell near the coolant outlet of the PEM fuel cell stack shows a more serious degradation caused by the HFR increase, which is also proved by the SEM analysis. The cross-section SEM analysis indicates that the dynamic cycle has a significantly negative effect on the catalyst layer, resulted in an obvious decrease on the thickness of the catalyst layer.
