Mini-review on degradation mechanism of perfluorosulfonic acid membranes induced by carboxylic end-groups

Perfluorinated ionomers with ionic sulfonic groups, i.e. perfluorosulfonic acid (PFSA) polymers, are among the most commonly used materials as a polymer electrolyte membrane (PEM) for hydrogen fuel cells. Despite the high chemical resistance of the C-F bond, which determines the use of this class of compounds, during the operation of the fuel cell, the membrane degrades, resulting in a significant deterioration in the operating parameters of the fuel cell. One of the reasons of degradation is the presence of terminal carboxyl groups in the PFSA polymers, which, under the attack of radicals, disintegrate with the formation of products that poison the catalyst and destroy the membrane. This review examines approaches to the study of degradation associated with the carboxylic end-groups, including both experimental data and modeling, and also provides an overview of approaches to modify the ionomer in order to reduce the concentration of carboxylic end-groups.