Enabling high-temperature application of Nafion membrane via imitating ionic clusters in proton conduction channels

Nafion membranes, representative of perfluorosulfonic acid (PFSA) proton exchange membranes are not effective in dehydrated state and high-temperature condition (>100 oC). The traditional hybrid modification would lower the mechanical strength of the membrane due to the large-scale phase separation. In this work, a hyperbranched polyamide (HBM) featuring high sulfonate concentration and nanoparticle morphology is synthesized and non-destructively filled into Nafion matrix to imitate the "ionic cluster" to accelerate the proton conduction at elevated temperature. During the non-destructively membrane modification, the Nafion PFSA membrane is swelled in the solution and the main chain structure is expanded, the HBM macromolecules is simultaneously filled into the membrane together with the solvent. After the removal of solvent, HBM end-capped with –COOH forms strong hydrogen bonds with the sulfonate groups in Nafion matrix. As a result, proton conductivity of the composite membrane can reach 0.047 S/cm, which is 1.9 times higher than that of the pristine Nafion membrane, at 110 oC and 60% RH. Given the excellent overall stability, fuel cell performance of the HBM-modified Nafion membrane is studied and a 30% increase in power density is observed, suggesting a viable strategy to expand the operation temperature of PFSA-based fuel cells.