A chemical-mechanical ex-situ aging of perfluorosulfonic-acid membranes for fuel cells: Impact on the structure and the functional properties

Abstract

Perfluorosulfonic acid (PFSA) membranes are key components for the operation of Polymer Electrolyte Membrane Fuel Cells (PEMFC). They undergo harsh conditions in terms of chemical environment and mechanical fatigue leading to irreversible degradations, up to their failure and to the Fuel Cell (FC) shutdown in worst cases. Through an ex-situ approach, this study aims to provide new insights about the impact of conjoint mechanical and chemical stresses on the structure and the functional properties of PFSA membranes. In this regard, various aging tests have been carried out using a custom-made device able to combine the application of a mechanical stress (sinusoidal profile) and the exposure to an environment containing free radicals ( i.e. Fenton's reagents). After about 20 h of accelerated aging test the analysis of the aged membranes permitted to demonstrate that the exposure to the combined stress significantly altered the morphology of Nafion™ XL membrane, with the appearance of bubbles close to the membrane surface and even delamination at the PFSA/reinforcement interface. On the other hand, and rather paradoxically, the water sorption and self-diffusion properties of the aged membranes as well as their cell performances remained satisfactory. • Nafion™ membranes were both exposed to chemical and mechanical stress simultaneously. • Coupling mechanical and chemical stresses induces important morphological changes. • Interfacial delamination of XL layers appeared after 20 h of conjoint stress. • Reinforcement layer in XL had little/lower effect on FER for severe solicitations.