330cm2燃料电池短堆怠速和额定功率动态循环1万次失效行为分析：极化性能、内阻、各节均一性、失效节位置、催化层厚度变化

Degradation behavior of a proton exchangemembrane fuel cell stack under dynamic cycles between idling and ratedcondition

Guangjin Wang

Fei Huang

Yi Yu

Sheng Wen

Zhengkai Tu

Abstract

The durability of proton exchange membrane（PEM） fuel cells is a key factor which prevents its commercial application onthe vehicle． Dynamic current cycle is one of the most common conditions for PEMfuel cells， especially varying the currents between the idling and the ratedcondition． To investigate the degradation behavior of fuel cells under thiskind of dynamic cycles， a PEM fuel cellstack with 330 cm2 active area is operated under 10，000 dynamic cycles with thecycling current density ranging from 25 mAcm−2 to 600 mAcm−2， which simulatescommon operating conditions in a vehicle cycle from the idling condition to therated condition． Polarization curves， the high－frequency resistance （HFR）， theuniformity of the individual cells， the performance degradation of PEM fuelcell stack at 25 mAcm−2 and 600 mAcm−2 are characterized to investigate theperformance 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 indicatethat the degradation rate of the stack is 1．0μVcycle−1 at 25 mAcm−2 under the idling condition． A more severe performancedegradation of about 2．0 μVcycle−1 is detected at 600 mAcm−2 under the ratedcondition． The individual cell nearthe coolant outlet of the PEM fuel cell stack shows a more serious degradationcaused by the HFR increase， which is also proved by the SEM analysis． Thecross－section SEM analysis indicates that the dynamic cycle has a significantlynegative effect on the catalyst layer， resulted in an obvious decrease on thethickness of the catalyst layer．

被测物：

The PEM fuel cell stack is composed of 10  single cells with a home－designed serpentine flow－field for the reacting gas．

Individual cells have an active surface  area of 330 cm 2．

the membrane was selected as Nafion 211．

The MEA is pressed between two graphite plates and cooling channel  on the back of each plate allowed deionizer water， at a pre－set temperature，  to cool the stack．

Fig． 1 e The schematic of the test  system．

Table 1 e Detail operation parameters of  the idling condition and the rated condition

Fig． 2 e Driving cycle protocol under  dynamic current

没有披露工况的时频细节，大约一个周期为60s，怠速30s，额定30s。1000个周期约1000分钟，167hr。

看上去过程中有明显的超调。

怠速接近于开路。

Fig． 3 e The polarization curves after  dynamic load cycles

Fig． 4 e The uniformity of the individual  cells at 25 mAcm－2 and 600 mAcm－2 （a） before and after dynamic load cycles，  （b） the voltage standard deviation before and after dynamic load cycles．

Fig． 5 e The HFR of individual cells at  25 mAcm－2 and 600 mAcm－2 before and after dynamic load cycles

After 10，000 cycles， the cell which was  closest to the outlet of the coolant water resulted in a higher HFR valueas  shown．

表明整堆中水出位置的电压是最低的。和第4图相对应。

从图4中电压两头低中间高的现象不明显，而图5中HFR的差异很明显。

the temperature distribution along the  fuel cell stack was investigated under different test condition and stack configurations．  The results found that the individual cell which was located near the coolant  outlet had a little higher temperature， which can result in a higher HFR．

这个图中的y轴可能是标错了，应该是欧cm2还差不多。

Fig． 6 e （a） The degradation rates at 25  mAcm－2 and 600 mAcm－2 after dynamic load cycles， （b） the average voltage  before and after dynamic load cycles

变载速度约0．2V／3s。

Fig． 7 e The degradation rates in  different intervals．

Fig． 8 e The surface SEM of （a） the fresh  MEA， （b） the fifth MEA and （c） the tenth MEA after dynamic load cycles

Fig． 9 e The cross－section SEM of （a） the  fresh MEA， （b） the fifth MEA and （c） the tenth MEA after dynamic load cycles

The catalyst layer also had a significant  decrease to 3．4 um for the tenth cell．

这样的工况能让阴极催化层厚度衰减到原始的35％，而性能差异并不是非常显著。这一点有点不好理解。

文中没有披露电堆操作压力。

Conclusions

Specific dynamic current cycles were  designed and applied to investigate the durability of a PEM fuel cell stack．  The degradation of the stack performance was evaluated by following the  voltage decrease rate．

Three main conclusions can be drawn from  above as followings．

（i）After 10，000 cycles， the degradation  rate of the stack voltage at 25 mAcm－2 is about 1．0uVcycle－1 ， however， at  the higher current the performance of the PEM fuel cell stack degraded more  quickly．

The  catalyst degradation under a high current is  still serious problems which need to be solved to improve the durability of  PEM fuel cell．

The  carbon corrosion reaction that takes place at the  electrode as a result of gross fuel starvation should be the direct cause of  the electro－catalyst＇s degradation under the high current such as at the  current density of 600 mAcm－2 in this study．

（ii）After large number of cycles， the degradation  rate and the recoverable performance are decreasing． Large－deltaV cycles are  associated to a maximum Pt surface area loss， which can result in the  unrecoverable performance degradation．

无TEM数据证明这一点。

（iii） The uniformity of individual cells  in PEM fuel cell stack decays with the cycling． The individual cell near the coolant water outlet resulted in a  higher degradation， which was proved by the Ohmic resistance and SEM  analysis． Interestingly， cells in the middle of the PEM fuel cell stack  resulted in a lower degradation． According to the degradation mechanisms  under different conditions， the system strategies must be designed properly  in order to improve the durability of PEM fuel cells．

对比阅读以下三篇文献，均为某一侧出现显著失效状态

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