چكيده به لاتين
Fully commercialization of polymer electrolyte fuel cell (PEFC) technology demands good performance and durability as well as reasonable price. However, hydrocarbon-based proton exchange membranes (PEMs), despite the fact they are potential alternatives to commonly used perfluorosulfonic acid membranes, experience premature failure in relative humidity cycles. In this study, an ex-situ method is used to investigate the progressive degradation of sulfonated poly ether ether ketone with degree of sulfonation of 64.75% in hygrothermal cycles for 700 minutes. Ex-situ examinations such as dimensional stability, mechanical properties and hydrogen leakage through specimens as well as morphological characterization included FE-SEM, AFM and XRD are employed for understanding of swelling-induced stress effects on SPEEK morphology. Results suggest that SPEEK due to simultaneous creep and exposure to elevated temperatures, encounters microstructural rearrangement in order to reduce the polymeric chains disorderliness and acts more brittle in the tensile test while elongation at break reduces by 87.3%. In addition, preexistent dead-end hydrophilic domains join each other to form more hydrophilic morphology within PEM and as a result water uptake increases. Furthermore, hydrogen cross-over rate increases due to (1) asymmetrical thinning, (2) micro-flaws formation in the thickness direction and (3) morphology evolution. We have demonstrated that mechanical degradation of SPEEK membrane is in a vicious circle, in other words, it is accelerating and consequently, lifetime estimation by using constant stress (and/or) stress amplitude is inaccurate.
