燃料电池气体扩散层的可压缩性：基材中PTFE含量、MPL中PTFE及含量、气体扩散层和密封复合、万能试验机刚度的影响

On the Compressibility of Gas DiffusionLayers in Proton Exchange Membrane Fuel Cells

M． S． Ismail

A． Hassanpour

D． B． Ingham

L． Ma

M． Pourkashanian

Abstract

The mechanical behavior under compressionfor a number of gas diffusion layers （GDLs） and a sealing gasket used in protonexchange membrane fuel cells （PEMFCs） has been investigated． The results showthat the stiffness of the carbonsubstrate increases with increasing polytetrafluoroethylene （PTFE） loading．Also， coating the carbon substrate withthe microporous layer （MPL） significantly enhances the stiffness of the GDL．On the other hand， the stiffness of theGDL appears to slightly decrease with an increase in the PTFE loading presentin the MPL． For a given practical compressive pressure， the mechanicalbehavior of the GDLs is hugely controlled by the less compressible sealinggaskets． Furthermore， it has been found that the compression curves for the tested materials must be corrected formachine compliance． Otherwise， the stiffness of the tested materials issignificantly underestimated．

The compression test was performed for circular samples using the INSTRON 5566 universal testing machine with a 10 kN load cell． The 10 mm diameter samples were die－cut and placed between two flat platens． a displacement rate of 1 mm min–1．

Table 1 PTFE loading of the tested carbon  substrates and MPL－coated GDLs．

（a）Provided by the supplier．

（b）Values for PTFE loading in the MPLs．  The base carbon substrate for these GDLs is SGL 10BA．

Table 2 The initial thickness of the  tested materials．

（a）Errors are calculated based on 95％  confidence interval．

Table 3 Compressive Young’s moduli in the  range from 1 to 3．2 MPa for the tested materials．

Fig． 1 （a） Compression curves for the  samples of the tested materials， and （b） a zoomed－in graph of the compression  curves for typical samples of the tested materials at low stresses．

Fig． 2 SEM images for （a） 10BA and （b）  10EA carbon substrates．

Fig． 3 SEM images for （a） 10BC and （b）  10BE GDLs．

Fig． 4 Compression curves for the  “GDL－plus－Gasket” sample and for typical samples of the GDL and the sealing  gasket．

将密封件和气体扩散层看作一体的复合材料进行力学处理。

Fig． 5 A fourth－order polynomial numerical  fit for “GDL－plus－Gasket” sample．

Fig． 6 Load－deformation curves for  typical samples of the tested materials and the machine material．

Fig． 7 Compression curves for the tested  materials with （filled data points） and without （empty data points）  correction for machine compliance．“WO” in the legends  stands for “without”．

把你设备刚度数据和文献中的比一下。10＾5N／mm

Table 4 Compressive Young’s moduli for  the tested materials， in the range 1–3．2 MPa， before and after correction for  machine compliance．

Conclusion

The mechanical behavior under compression  for a number of GDLs and a sealing gasket has been investigated． The results  show that the stiffness of the carbon substrate increases with an increase in  the PTFE loading． This could be explained by （i） the reduction in the porosity of the carbon substrate， and （ii）  the increased binding effects of the PTFE material． Also， coating the  carbon substrate with an MPL significantly enhances the stiffness of the GDL．  This could be attributed to （i） the  presence of two mechanical resistances in series （i．e．， the carbon substrate  and the MPL）， and （ii） the formation of an “interphase” layer between the  carbon substrate

and  the MPL， which is reinforced with carbon fibers．

力学性能测试使用基础材料测试是不够的。需要使用实际材料，材料的配方变化对于力学特性有着巨大影响。

In  contrast， the stiffness of the GDL appears to slightly decrease with an  increase in the PTFE loading in the MPL． This is most likely due to the  increase in the porosity of the MPL of the GDL that has been treated with a  higher amount of PTFE in its MPL．

The results also show that if the GDL is  encircled with a sealing gasket， as is normally the case inside the fuel  cell， the compression ratio of the  GDL， for a given practical compressive pressure， is dominantly controlled by  the sealing gasket．

这个结论不一定对，在作者使用的材料体系中是这样。

Therefore， for practical PEM fuel cell  systems， the initial thickness and the compressibility of the sealing gasket  must be taken into account if the mechanical behavior of the GDL inside the  fuel cell is investigated． Also， the experimental data should be corrected  for machine compliance． Otherwise， a significant underestimation in the stiffness  of the tested materials is obtained． Potential future works may address （i）  the optimization of the compressibility and the initial thickness of the  sealing gaskets in order to have a maximum fuel cell performance and a premium  contact between the GDL and the bipolar plate， and （ii） the relation between the fuel cell performance and both the stiffness  of the GDL and the compressive pressure on the GDL．