Understanding the formation of pinholes in PFSA membranes with the essential work of fracture （EWF）

E． Moukheiber

C． Bas

L． Flandin

Abstract

One of the most harmful degradation process in PEM fuel cell is the development of pinholes in the membrane． There is therefore a need for an effective experimental characterization to allow ab initio membrane comparison． In this paper， the mechanical fracture resistance of various PFSA membranes was studied using the essential work of fracture （EWF） and tensile tests． PTFE reinforced membrane better resists pinholes formation due to its high resistance to crack initiation and propagation． Additionally， energy partitioning showed that the necking and tearing stage of the layered structure membrane accounts for the main part of the total fracture energy due to enhanced plastic deformation of PTFE． Moreover， cracks were found to initiate and propagate easily in the direction parallel to the polymer chains which suggest that the fracture control could be optimized by pointing the direction of the gas channel perpendicularly to the orientation of the polymer chains， i．e． to rolling process during manufacturing． Finally， EWF technique was found to be more relevant for assessing the differences in the mechanical behaviour of the membranes compared to standard tensile tests．

短侧链和长侧链的膜化学结构

实验材料

双边缺口拉伸试验Double edge notched tensile test（DENT）破裂区和塑性区

需要更深入的了解EWF方法可以参考

Application of the essential work of fracture （EWF） concept for polymers， related blends and composites： A review

https：／／doi．org／10．1016／j．progpolymsci．2010．07．001

缺口方向性

常规力和位移曲线中三种电解质膜明显的各向异性现象

双边缺口拉伸试验下三种电解质膜的各向异性现象

EWF方法下断裂功

EWF方法中的参数

从破裂功的比较上可以看出选材时XL－100＞＞SSC－110＞LSC－110

两种样品的比较，拉伸破裂时的连接宽度与力和位移。

比较形象的示意图

Conclusion

In summary， the EWF tests were found more discriminative
compared to standard tensile tests in assessing the mechanical
behaviour of PFSA membrane and is more representative
of membrane fracture in fuel cell． The better mechanical
behaviour of composite XL－100 compared to non－reinforced
membranes could be explained by a better resistance to
crack initiation characterized by a higher essential work of
fraction We and a better resistance to crack propagation
characterized by a higher slope bwp． In addition， energy partitioning
of XL100 showed that the resistance to crack propagation
stage accounts for the main part of the total fracture
energy due to PTFE blunting． For all samples， the TD－notch
specimens displayed the highest resistance to fracture
which means that the rupture of the membrane is difficult
when pointing across the polymer chains． Since water and gas
channels are plausible sources to the appearance of defects or
fractures in the membranes due to their sharp edges under
the compression of the stack， the orientation of polymer chain in comparison to channels should be an important parameter
to take into account during the manufacturing and the processing
of AMEs． The best configuration would be to point the
direction of the gas channels perpendicularly to the orientation
of the chain polymers in the membrane in order to optimize
the tear resistance． A schematic representation of the
tear resistance optimization during AME process is presented
in Fig． 10．

使用增强型电解质膜可以视为缓解干湿循环的机械因素造成燃料电池电极质膜失效的五种方法（其一）

而流道方向和聚合物链方向尽量垂直，应该可以视为缓解干湿循环的机械因素造成燃料电池电极质膜失效的五种方法（其四）