电解质膜添加氧化铈对燃料电池活化过程的影响

Understanding of Nafion Membrane Additive Behaviors in Proton Exchange Membrane Fuel Cell Conditioning

Nana Zhao，                                                    

Zhong Xie，                                    

Zhiqing Shi

Durability and cost are the two major factors limiting the large－scale implementation of fuel cell technology for use in commercial， residential， or transportation applications． The conditioning cost is usually negligible for making proton exchange membrane fuel cells （PEMFCs） at R＆D or demo stage with several tens of stacks each year． However， with industry＇s focus shifting from component development to commercial high－volume manufacturing， the conditioning process requires significant additional capital investments and operating costs， thus becomes one of the bottlenecks for PEMFC manufacturing， particularly at a high production volume （＞1000 stack／year）． To understand the mechanisms behind PEMFC conditioning， and to potentially reduce conditioning time or even to eliminate the conditioning process， the conditioning behaviors of commercial Nafion™ XL100 and Nafion® NRE 211 membranes were studied． The potential effects of the membrane additive on fuel cell conditioning were diagnosed using in situ electrochemical impedance spectroscopy （EIS）． It was found that the membrane additive led to the significant variation of the charge transfer resistance in EIS during conditioning， which affected the conditioning behavior of the membrane electrode assembly （MEA）．

Both membranes present a similar ion exchange capacity （IEC， 1．0 mmol／g （New Castle， DE））． NRE－211 is a monolayer and its thickness is 25．4 um， while XL－100 is a perfluorosulfonic acid （PFSA）－based membrane with an additional microporous central polytetrafluoroethylene （PTFE） layer and its thickness is 27．5 um． NRE－211 does not contain any additives， while XL－100 contains ion－exchanged cerium as additive to provide resistance to peroxide attack．

这篇文章讲的是膜内氧化铈对燃料电池活化的影响。但膜的结构不同，不是单因素比较，严格地说，应该在Nafion－211的制备过程中添加氧化铈，或者通过萃取把XL－100里面的氧化铈除掉，或者自己做膜来进行氧化铈添加与否的比较。

Fig． 1 H2／air－conditioning curve of NRE－211 membrane based
MEA

Fig． 2 In situ electrochemical impedance spectra of NRE－211
membrane based MEA over conditioning time at a current density
of 0．8 A／cm2

Fig． 4 H2／air conditioning curve of XL－100 membrane based
MEA

两种膜在活化过程中的HFR的变化趋势的确不同。

Fig． 5 In situ electrochemical impedance spectra of XL－100
membrane based MEA over conditioning time at a current density
of 0．8 A／cm2

Fig． 3 （a） Simulated charge transfer resistance （Rct） and （b） simulated mass transfer resistance （Rms） of MEAs during conditioning
at a current density of 0．8 A cm－2

Fig． 6 iR－compensated conditioning curves of the MEAs
at a current density of 0．8 A cm－2

这是原图，检索全文没搞懂什么是Infrared－compensated conditioning curves，还是老老实实看看原文。In order to eliminate the effect of the membrane resistance on the conditioning curves， the current－resistance （iR） compensated conditioning curves are plotted in Fig． 6．才明白这个地方是把iR内阻补偿写成IR，不知道被谁误以为是IR红外光谱的意思了。

Fig． 7 Comparisons of in situ EIS between NRE－211 membrane and XL－100 membrane－based MEAs with conditioning time at （a） 5 min， （b） 30 min， （c） 4 h， and （d） 16h

Conclusions

In summary， the conditioning behaviors of commercial XL－100
and NRE－211 membranes were studied and the potential effects
of membrane additive on fuel cell conditioning were diagnosed
using in situ EIS． It was found that the membrane additive led to
the significant variation of the Rct during conditioning． Specifically，
XL－100 membrane－based MEA shows inferior fuel cell performance
to the NRE－211 membrane－based MEA mainly due to
the higher Rct during conditioning． The phenomena could be
explained by the contamination of catalyst layer caused by cerium
migration from XL－100 membrane into catalyst layer and therefore
a decrease of protonic conductivity／concentration in catalyst
layer． Although further studies such as ex situ physical characterizations and other electrochemical characterization are required to
draw a solid conclusion on this phenomenon， this work shows that in situ EIS is an effective diagnostic tool to identify the underlying
mechanisms of conditioning．