1．4V高电位循环条件下聚合物膜燃料电池的失效分析：碳腐蚀、铂带和金属双极板离子污染

Degradation behavior of a polymerelectrolyte membrane fuel cell employing metallic bipolar plates under reversecurrent condition

KwangSupEom

EunAe Cho

Suk－WooNam

Tae－HoonLim

Jong HyunJang

Hyoung－JuhnKim

Bo KiHong

Yoo ChangYang

a b s t r a c t

To examine durability of metallic bipolarplates （BPs） under reverse current conditions， the degradation of PEMFCemploying graphite， bare 316L， and CrN－coated 316L BPs is investigatedvia a 1．4 V pulse cycling test． After 20 cycles， the average voltage decay rateat 160 mA cm−2 is 6．8， 16．8， and 12．0 mV cycle−1 for the single cell using graphite， bare 316L， and CrN－coated 316LBPs， respectively． SEM， EPMA， and TEM analyses of the cathodes that experiencedan extraordinary high voltage of 1．4 V show that carbon corrosion and Ptmigration／agglomeration occur similarly for the single cells， irrespective ofthe bipolar plate material． In contrast， in the membrane tested withbare 316L and CrN－coated 316L， Fe and Cr are detected； the amounts of Fe and Crin the membrane are higher for bare 316L than for CrN－coated 316L． Themembrane contamination results in a decrease in the ionic conductivityof the membranes， which mainly contributes to the faster performancedecay of the single cells employing bare 316L and CrN－coated 316L bipolarplates． Thus， if automotive PEMFCs using metallic BPs are exposed to reversecurrent conditions upon start／stop cycles， metal contamination of themembrane could accelerate the performance decay in addition to thecathode degradation， such as carbon corrosion and Pt migration／agglomeration．

Fig． 1． Illustration of the 1．4 V pulsecycle employed in this study to accelerate the degradation of the cellperformance under the reverse current condition upon start／stop cycles

阴极高电位循环，1．4V总长120分钟（2小时）

Fig． 2． Effects of 1．4 V pulse cycling onthe i–V curves for the single cells employing （a） graphite， （b） bare 316L， and（c） CrN－coated 316 L BPs． （d） Cell voltage at 160 mA cm−2 as a function of the cycle number．

有氮化铬涂层的金属双极板前5个循环性能就出现衰减，这个有些异常。

Fig． 3． i–V curves for the single cellemploying a fresh MEA／fresh BPs and a fresh MEA／aged BPs： （a） bare 316L and （b）CrN－coated 316L BPs．

膜电极本身、双极板材料对膜电极两方面对性能产生了很大的影响

Fig． 4． SEM surface images for the cathode（a） before and after 20 cycles with （b） graphite， （c） bare 316L and （d）CrN－coated 316L BPs．

Fig． 5． Cross－sectional SEM images for theMEAs observed （a） before and after 20 cycles with （b） graphite， （c） bare 316Land （d） CrN－coated 316L BPs．

碳腐蚀的催化层减薄和铂带

Fig． 6． Cross－sectional back－scatteredelectron microscopy （BSEM） （left） and EPMA （right， mapped for Pt） images forthe MEAs （a） before and after 20 cycles with （b） graphite， （c） bare 316L and（d） CrN－coated 316L BPs．

阳极催化层厚度未发生变化，阴极催化层从11微米减薄至4．5微米

Table 1

Average particle sizes of the Pt catalystfor the cathode employing graphite， bare

316L and CrN－coated 316L BPs measuredbefore and after 1．4 V pulse cycles．

Fig． 7． TEM bright－field images for thecathode Pt／C catalyst （a） before and after 20 cycles with （b） graphite， （c）bare 316L and （d） CrN－coated 316L BPs．

Fig． 8． TOF－SIMS spectra for （a） Fe and （b）Cr in the membranes before and after 20 cycles with graphite， bare 316L andCrN－coated 316L BPs．

使用氮化铬涂层，和无涂层的相比，膜电极中铁的成分收到抑制，但铬的成分轻微增加（两个图的纵坐标不一样）。但是没有更为严格的定量数据，比如铁的ug／cm2，在阳极还是在阴极或者膜内部。

Table 2

Through－plane proton conductivity of themembrane employing graphite， bare 316L and CrN－coated 316L BPs measured beforeand after 1．4 V pulse cycles．

金属双极板的质子电导出现显著下降。

Fig． 9． Nyquist plots for measuring protonconductivity of the membranes before and after 20 cycles with graphite， bare316L and CrN－coated 316L BPs using the 4－probe electrodes technique．

如果在文章中有常规电位循环下的电极失效分析，高电位下双极板的腐蚀状态、离线高电位下平板的腐蚀状态对比就更有趣了。

Conclusions

The degradation of automotive PEMFCsemploying bare 316L and CrN－coated 316L BPs in comparison with graphite BPs wasinvestigated via 1．4 V pulse cycling． By being repetitively exposed to 1．4 V，the cell voltage at 160 mA cm−2 decreased at a decay rate

of 6．8， 16．8， and 12．0 mV cycle−1 for graphite， bare 316L and metal nitride （CrN）－coated 316L BPs，respectively． During the 1．4 V pulse cycling， the cathode degradation duecarbon corrosion and Pt migration／agglomeration occurred similarly for all theMEAs using graphite， bare 316L and CrN－coated 316L BPs． In contrast， themembrane degradation due to metal ion contamination was observed only in themembranes cycled with metallic BPs， and the amount of metal contamination wasreduced by coating bare 316L with metal nitride． The dissolution of metal ions reducedthe ionic conductivity of the membrane and contributed to the faster decreaseof the cell performance．