Counter-ion Dynamics and the Mechanical Properties of Fuel Cell Membranes

roethylene and generally less than 15 mol % of perfluorovinyl ether units that are terminated with a sulfonic acid exchange site. The most widely studied PFSI and the focus of this study, Nafion, is a product of the E. I. DuPont Chemical Company (Fig. 1). The polar perfluoroether side-chains containing the ionic sulfonate groups aggregate, thus leading to a nanophase-separated morphology where the ionic domains, termed clusters, are distributed throughout the non-polar polytetrafluoroethylene (PTFE) matrix. This morphology gives a characteristic scattering peak in small angle x-ray scattering at Q ≈ 0.2 Å-1. The membranes used in this study have been neutralized with tetramethyl (TMA+) and tetrabutyl (TBA+) ammonium counter-ions (Fig. 1). The size difference between these two counter-ions acts to change the strength of the electrostatic interactions, thus changing the chain dynamics and, in turn, the mechanical properties [1, 2].