配合不锈钢金属双极板燃料电池调变气体扩散层疏水特性：双极板的接触角时间效应、低温高湿、高温低湿加压的性能差异

Optimization of GDLs for high－performancePEMFC employing stainless steel bipolar plates

KwangSup Eom

EunAe Cho

JongHyun Jang

Hyoung－Juhn Kim

Tae－Hoon Lim

Bo Ki Hong

Jong Hyun Lee

Abstract

The effects ofpolytetraflouroethylene （PTFE） content in the gas diffusion layer （GDL） on the performanceof PEMFCs with stainless－steel bipolar plates are studied under various operationconditions， including relative humidity， cell temperature， and gas pressure．The optimal PTFE content in the GDL strongly depends on the cell temperatureand gas pressure． Under unpressurized conditions， the best cell performance wasobtained by the GDL without PTFE， at a cell temperature of 65 C and relativehumidity （RH） of 100％． However， under the conditions of high cell temperature（80 C）， low RH （25％） and no applied gas pressure， which is more desirable forfuel cell vehicle （FCV） applications， the GDL with 30 wt．％ PTFE shows the bestperformance． The GDL with 30 wt．％ PTFE impedes the removal of produced waterand increases the actual humidity within the membrane electrode assembly （MEA）．A gas pressure of 1 bar in the cell using the GDL with 30 wt．％ PTFE greatlyimproves the performance， especially at low RH， resulting in performance that exceedsthat of the cell under no gas pressure and high RH of 100％．

Fig． 1 e Contact angles of waterdroplets on the surface of （a） graphite and （b） stainless－steel bipolar plateswith contact times of （1） 20， （2） 90， （3） 180， and （4） 300 s．

接触角的测量值竟然和接触时间有关联。以前并未关注到这一现象。石墨受这个因素的影响更加明显。不清楚时间的这个因素对于电池运行具体意味着什么，应该以一个什么时间来关联接触角特性和亲疏水性。

However， upon an increase in contacttime from 20 to 300 s， the water contact angle of the graphite decreased significantlyfrom 90 to 36 ， probably due to many micro－pores in the graphite plate．

文中并未提及双极板的涂层信息。

Fig． 2 e Cross－sectional SEM imagesof the GDLs without PTFE： （a） the whole image of GDL with triple layers， （b）the top layer with carbon power， （c） the middle layer mixed with carbon powderand carbon fiber， and （d） the bottom layer composed of carbon fiber．

Fig． 3 e Surface morphologies ofmacro－porous substrate sides of GDLs with various PTFE contents in substrate rangingfrom 0 to 20 wt．％： （a） 0， （b） 5， （c） 10， （d） 20 and （e）30 wt．％．

Table 1 e Effects of PTFE content inthe macro－porous substrates of GDLs on water contact angle， air and waterpermeation， and through－plane electrical resistance．

更改基材中的PTFE含量MPL的接触角数据竟然也会发生变化。

30％PTFE条件下垂直气体扩散层的面电阻是not detected。

the water permeation and electricalresistance are more affected by the presence of PTFE itself， while the airpermeation decreases gradually with PTFE content．

Fig． 4 e Effects of RH and PTFEcontent （0－30 wt．％） in substrate of GDLs on the cell performance： （a） 25／25，（b） 50／50， and （c）100％／100％ RH conditions （anode／cathode）． The currentdensities at 0．6 V are shown in （d）．

同一个燃料电池产品并不是在高湿条件下性能高就意味着它在低湿条件下性能好。而需要考虑系统的增湿能力来选择合适的膜电极产品。

Higher PTFE content resulted in adecrease in porosity and an increase in water retention amount， causing adecrease in membrane resistance and improvement of cell performance by keepingmore water inside the MEA at low RH of reactant gases．

Fig． 5 e Effects of RH of inletgases on the I－V performance （a－b）， impedance plots （c－d）， and the CV spectrum（e－f） of single cells employing GDLs without PTFE （（a）， （c）， and （e）） and with20 wt．％ PTFE （（b）， （d）， and （f））． EAS calculated by （a） and （b） is shown in（g）．

ECSA的测量结果原线和离线相互一致才有意义。

Table 2 e The ohmic and chargetransfer resistance of the cell using GDLs with 0 and 20 wt．％ PTFE contentunder various gas RHs conditions， as measured by EIS．

Fig． 6 e Current densities at 0．6 Vwhen using GDLs with various PTFE contents （0－30 wt．％） at cell temperatures of65 and 80 C and RH of （a） 25， （b） 50， and （c） 100％．

Fig． 7 e Charge transfer resistancesof single cells employing GDLs with various PTFE contents （0－30 wt．％） at 65 Cand 80 C at 50％ RH．

Fig． 8 e Performances of singlecells employing GDLs with various PTFE contents （0－30 wt．％） under operatingconditions of 80 C， 25 and 100％ RHs， and 0－1 bar：（a） 0 wt．％ PTFE； （b） 5 wt．％PTFE； （c） 10 wt．％ PTFE； （d） 20 wt．％ PTFE； （e） 30 wt．％ PTFE． The currentdensities at 0．6 V are shown in （f）．

Table 3 e Open circuit voltagevalues measured in the cells using GDLs with various PTFE contents （0－20 wt．％）under various gas pressures conditions．

Table 4 e Ohmic and charge transferresistances at 80 C when using GDLs with various PTFE contents under various operatingconditions．

Fig． 9 e CV spectra of single cellsusing GDLs with PTFE content of （a） 0 wt．％ and （b） 20 wt．％ under operatingconditions of 80 C， 25 and 100％ RHs， and 0－1 bar． The EAS is shown in （c）．

Conclusions

We investigated the effects of PTFEcontent （0－30 wt．％） in the macro－porous substrate of GDLs on the performancesof PEMFCs with stainless－steel bipolar plates under various operatingconditions． An increase in the cell temperature from 65 to 80 C increased thecharge transfer resistance significantly， leading to a decrease in the cellperformance． With an increase in gas pressure， the cell performance increasedas a result of a decrease in the charge transfer resistance and an increase inthe EAS． The optimized PTFE content in the GDL to achieve high cellperformances depended strongly on the cell temperature and gas pressure． Underrelatively low temperature （65 C）， high RH （100％）， and unpressurizedconditions， the GDL without PTFE exhibited the highest cell performance．Under higher cell temperature （80 C）， lower RH （25％）， and unpressurizedconditions， however， the GDL with the highest PTFE content of 30 wt．％ showedthe highest cell performance． This may result from the fact that the higher amountof PTFE in GDL impedes the removal of product water from MEA to the metallicbipolar plate due to the reduced porosity of the GDL， causing enhanced waterretention and actual RH within MEA． The gas pressure of 1 bar in the cellusing the GDL with 30 wt．％ PTFE significantly improved the cell performance，especially at low RH， resulting in performance exceeding that of the cell underno gas pressure and RH of 100％．

温度80度时，空气加压1bar，湿度25％和空气常压，湿度100％两个操作条件给系统设计选择，系统会更倾向于前者。