Solid-state NMR study of two classic proton conducting polymers: Nafion and sulfonated poly(ether ether ketone)s

Proton mobilities in Nafion and sulfonated poly(ether ether ketone) (S-PEEK) have been studied using high-resolution solid-state H-1 NMR under fast magic angle spinning (MAS). These studies demonstrated proton exchange between sulfonic acid groups and water within both Nafion and S-PEEK. Variable temperature experiments were used to determine the activation energy for proton transport in pure Nafion, found to be 11.0 kJ/mol, which is lower than those determined for S-PEEKs with different degrees of sulfonation. Increasing proton exchange rates with increasing temperature indicate the expected dependence of proton mobility on temperature. A rotor-synchronized homonuclear double quantum filter sequence (BaBa) was used to disclose the nature of the H-bonding interactions in the two polymers, from which a model of the proton interactions in the polymers is developed.