Relationship between polymer structure and dry-wet cycling resistance of perfluorosulfonic acid membranes

Perfluorosulfonic acid (PFSA) polymers are used as electrolyte membranes in polymer electrolyte fuel cells. In this study, the relationship between the molecular weight and dry-wet cycle resistance of the polymer was investigated. PFSA polymers with various molecular weights were synthesized and characterized. The results showed that the polymer with lower molecular weight had lower dry-wet cycle resistance and showed a change in the periodic structure of the clusters after the dry-wet cycling test along with an increase in the crystallinity. It was inferred that the local stresses associated with this structural change also accelerated macroscopic structural changes, leading to film rupture. By contrast, the polymers with high molecular weights showed high resistance to dry-wet cycling because of their low initial crystallinity and subsequent poor crystal growth, in addition to their strong molecular chain entanglement characteristics.