Carboxylic End-Group in Perfluorinated Ionomers: Degradation Mechanism and Modification

Perfluorinated ionomers with ionic sulfonic groups 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 od degradation is the presence of terminal carboxyl groups in the ionomer, 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 group, 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.