燃料电池电堆电池位置相关（电堆后部、空气侧入口）性能加速衰减的催化层结构失效分析

Mechanistic insight into the accelerateddecay of fuel cells from catalyst－layer structural failure

Zunyan Hu

Liangfei Xu

Jianqiu Li

Qing Wang

Yangbin Shao

Xiaojing Chen

Wei Dai

Minggao Ouyang

Abstract

The nonlinear， accelerated decline of fuel cellsis a major cause of diminished service life， which is difficult to be detectedin early warning． Through in situ electrochemical diagnosis， we found that theaccelerated decline of fuel cell could not be directly predicted by thecrossover current or the electrochemically active surface area． Surfaceanalysis of catalyst layer showed that the inverse flow of the cathode andanode may lead to dry－wet cyclic stress and corrosion of the catalyst layer inthe cathode inlet area （anode outlet area）． This leads to cracking in thecatalyst layer and corrosion of the carbon support． What’s more， theuncorroded electrolyte will then fill in the original microporous structure，resulting in a decrease in the porosity of the catalyst layer and a correspondingaccelerated decline its mass－transfer performance． According to asemi－quantitative model， a 50％ corrosion of the catalyst layer leads to adecrease of up to 80％ in the equivalent diffusion coefficient， the key mechanisminducing the local performance decline， which leads to accelerated decline ofthe overall fuel cell performance． This is particularly important for vehiclefuel cells where the local deterioration caused by the uneven distributionof hydrothermal states induces accelerated decline．

工况是失效比较关键的因素，而文中并未介绍，对于工程类似问题的借鉴被打了折扣。

Based on a big data analysis of more than  100 demonstration fuel cell vehicles， Shenli Co．， Ltd． proposed an  Accelerated stress test （AST） protocol with an acceleration factor of 3．8 for  this test．

Fig． 1． fuel cell basic information．

Fig． 2． GSC analysis results during AST  experiments．

GSC： galvanostatic charge

Fig． 3． Polarization curve tests before  and after AST experiments， Anode／cathode gas humidity is 80％ and 30％ ＠ 65 ◦C， gas pressure is about 150 kPa．

Fig． 4． Distribution of sampling points  of a large－format fuel cell．

Table 1 Contact angle test．

Fig． 5． Cross－sectional SEM images from  cell A．

Fig． 6． Surface SEM images of cell A．

关于催化层裂纹没有给出对标节CellB、Cell C耐久性后的表面状态。

Fig． 7． Surface structure of CCL．

关于催化层孔结构没有给出对标节Cell B、Cell C耐久性后的表面状态。

Fig． 8． Surface EDS analysis．

结论中还提到这一点，这个证据有点牵强，EDX很少用某一个元素的实测质量百分含量直接进行定量。

Fig． 9． Schematic of catalyst layer  degradation．

Fig． 10． Porosity degradation sensitivity  analysis．

r％ is the remaining percent of the  initial dissociative electrolyte

Fig． 11． Concentration overpotential  analysis．

q％ is the volume fraction of the  electrolyte

s Bruggeman equation中的系数

Conclusions

This paper presents a detailed analysis ofthe accelerated decline processes of a large－format fuel cell． Some possiblefactors have been proposed and studied to explain the inducement of cellfailure． Normally， inconsistency and nonuniformity degradation are the key factorsof large－format fuel cell stack failure， and it’s hard to be observed byvoltage monitor or ECSA estimation in the early stages．

Material analysis shows the cathodeinlet （anode outlet） area is the weak spot for the fuel cell stack with theinverse flow structure of the cathode and anode． The MEA of the cathodeinlet （anode outlet） area suffers dry－wet cyclic stress and corrosion ofthe catalyst layer． This leads to cracking in the catalyst layer andcorrosion of the carbon support， which is about 40％． Residualuncorroded electrolyte fills in the original microporous structure， resultingin a 2．38－fold increase in electrolyte percentage． The surface of CCLbecomes dense and rugged， resulting in a decrease in the porosity of thecatalyst layer． And the degradation of mass and heat transfer performance inCCL is the direct cause of the nonlinear， accelerated decline of fuel cell．

More importantly， ECSA decline is coupledto mass transfer performance degradation． Semi－quantitative analysis shows that50％ corrosion of the catalyst layer leads to a decrease of up to 80％ in the equivalentdiffusion coefficient， the key mechanism inducing the local performancedecline， which leads to accelerated decline of the overall fuel cellperformance． And the degradation characteristics of voltage drop and diffusioncoefficient decline are similar in the full life circle．

In conclusion， the structural deteriorationof the catalyst layer contributes more to the accelerated decline than anyother cause． Material， structure design， and control optimization should becombined to relieve this problem to extend the lifetime of fuel cell stack．

文章没有谈Cell A和其他节差异的原因（有实验结果无表征对比），只介绍了Cell A不同区域差异的原因。