燃料電池車輛用電池失效分析中膜電極針孔的四種檢測(cè)方法研究
Comparative study of pinhole detection methods for automotive fuel cell degradation analysis

?Michael Obermaiera????????????????????????????????????????????????????????????????????     Krzysztof Jozwiaka

Markus Raubera     Andreas  Bauera

ChristinaScheubc

Abstract

Knowledge gained by fuel cell degradation analysis is important for meeting durability targets and thus for the commercialization of polymer electrolyte membrane fuel cells． Herein， the application of the most appropriate characterization method is crucial depending on which degradation mode is dominating． One major failure mode in polymer electrolyte membrane fuel cells is the formation of pinholes in the polymer membrane． In this work， a systematic study of four promising methods for pinhole detection is performed， namely detection via infrared camera， via He－gas detection as well as via pressure drop and hydrogen crossover measurements between anode and cathode． In particular， detection limits as well as influences of the material system and other relevant factors are discussed． Finally， a comparison of the different methods and a recommendation for their practical application is given to optimize detection of membrane defects in the field of failure analysis． The most successful ones are then tested for the analysis of real automotive stacks before and after operation．

耐久測(cè)試后的電極圖像，雖然看上去還好，

但作者是專家，看出厚度下降，陰極孔隙率下降（影響氣體滲透），MPL粘附，鉑沉積（ECSA下降）。

Fig． 1 （D） illustrates the severe thickness decrease and the complete porosity loss of the cathode electrode as well as MPL adhesion and Pt deposition on top of the degraded cathode electrode． This altered cathode electrode porosity can lead to a strong decrease in gas permeability towards electrochemicalactive sites． In addition， Pt deposition on top of the degraded cathode electrode （see Fig． 1 （D）） and Pt crystallite growth of up to 100％ compared to begin of life reference samples， as measured with X－ray diffraction， were found． This indicates a decrease in electrochemical active surface area．

實(shí)際針孔的大小為40微米。

GDE／GDL thickness are measured with a universal micrometer （Frank PTI 16502， tip diameter 5 mm， applied pressure 125．2 kPa）．厚度計(jì)的測(cè)量壓強(qiáng)是125kPa。

第一種針孔檢測(cè)技術(shù)：紅外熱成像法

針孔為200微米時(shí)，紅外熱成像法可以獲得的定位信息。

GDE電極不同，熱導(dǎo)不同，同樣的熱棒，檢測(cè)到的溫度有4度的差異。

不同的材料體系下，不同的針孔尺寸造成的局部溫度上升。電極材料不同，熱導(dǎo)不同，檢測(cè)到的溫度最大偏差可以達(dá)到16度。有的材料體系對(duì)針孔敏感，而有的材料體系對(duì)針孔并不敏感。

沒(méi)有針孔的條件下的溫度梯度并不可靠，大功率燃料電池的材料缺陷無(wú)處不在。

針孔尺寸進(jìn)一步縮小，到30－50微米狀態(tài)，氫氧壓差逐漸增加時(shí)，模擬電池的局部溫升最大為3度，而真實(shí)電池和電極材料的選擇相關(guān)，最大8度，小的為3度。

而且氣體擴(kuò)散層的覆蓋會(huì)影響局部溫升的測(cè)量，小氫氧壓差下有的會(huì)造成35的偏差，有的偏差僅僅3度。

Within this MEA， two pinholes with diameters of approximately 10
μm and 20 μm are found with microscopic investigation． These pinholes could however not be detected with IR－thermography。說(shuō)明了檢測(cè)下限

第二種針孔檢測(cè)技術(shù)：氦檢，檢測(cè)范圍在5－10微米。但是這種方法的測(cè)試結(jié)果和探頭的尺寸竟然有關(guān)系。使用不同的材料，膜的針孔大小相同，使用不同的探頭尺寸測(cè)試到的氦流量竟然不同。

使用假電極，幾乎無(wú)氦流量，而是用Nafion電極，氦流量約2個(gè)單位。氫氧壓差50kPa，5微米針孔，氦流量約2個(gè)單位－4個(gè)單位。10微米針孔，氦流量約4個(gè)單位－8個(gè)單位。

第三種針孔檢測(cè)技術(shù)：壓降法。

第四種針孔檢測(cè)技術(shù)：電化學(xué)法。

第五種針孔檢測(cè)技術(shù)：同向供氣循環(huán)開(kāi)路加速測(cè)試下的燃料電池質(zhì)子交換膜失效

第五種方法的檢測(cè)限也大致在5微米。

第六種針孔檢測(cè)技術(shù)：光學(xué)顯微鏡

作者總結(jié)如下

作者的表格中有筆誤，讀者可以挑挑錯(cuò)。

Conclusion

Four promising methods for pinhole detection， namely detection via
infrared－thermography， helium－gas detection， pressure drop and
hydrogen crossover measurements， are investigated and compared by
means of their detection limits and dependencies e．g． on the material
system such as Pt loading and morphology of the carbon network．
Pressure drop and hydrogen crossover measurements are found to be
fast and relatively easy implementable methods with detectable pinhole diameters of approximately 100 μm and 40 μm for the investigated material and the used test station， respectively． Herein， detection limits of pressure drop and hydrogen crossover methods depend on material properties of the investigated MEA． Detection of reaction heat of crossover hydrogen by infrared－thermography and detection of heliumgas concentration above a pinhole require additional cell hardware with a perforated clamping plate． Detection by infrared－thermography enables a fast localization of pinholes． Detected pinhole sizes are strongly dependent on both electrode and GDL properties as well as on hardware positioning and varies between diameters of 10 μm and 100 μm for the investigated materials． For the material system used in this work， the use of a helium－gas detector enables the localization of pinholes with a diameter of 5 μm （smallest pinhole size that we could fabricate）， with the detection limit being dependent on GDL gas permeability and hardware positioning． Scanning of the whole MEA is more time consuming as for other methods． Due to the diversity of membrane degradation， different analysis tasks may arise ranging from fast screening of a general membrane failure to a sensitive localization of small pinholes． Therefore， a comparison of the different methods and a suggestion for their application is given． The detection of membrane defects of MEAs from two automotive stacks demonstrates the applicability of the infrared－thermography and helium－gas detection in an automotive failure analysis process． In total， we suggest an assembly of different pinhole detection methods for an appropriate pinhole analysis．

       原文標(biāo)題 : 燃料電池車輛用電池失效分析中膜電極?針孔的四種檢測(cè)方法研究