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

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.