Investigation of structural and transport properties of highly oxygen-permeable ionomer in polymer electrolyte membrane fuel cells using molecular dynamics simulations

Understanding the nanostructure of ionomer membranes is important for elucidating the mechanism of their molecular transport properties and for improving the performance of proton exchange membrane fuel cells. In this study, we incorporated a ring structure into the main chain of perfluorinated sulfonic acids ionomers including short side chain (SSC) as a highly oxygen-permeable ionomer and used molecular dynamics simulations to investigate the interrelation between the structural properties of the ionomer and its transport properties. The incorporated ring structure influences the stiffness of the ionomer chain and the nanostructure of the ionomer membrane. To demonstrate the influence of the ionomer structure on the transport properties and the nanostructural features such as water channels, the structure and water volume were analyzed and the water-cluster connectivity was calculated for modified SSC ionomers and long side chain (LSC) ionomer, and the results were compared. Compared with the LSC ionomer, the modified SSC ionomer exhibits better oxygen transport properties but worse water transport properties because of its stiff chain derived from the ring structure.