Molecular Complexation of Polymers and Metal Oxide Clusters for Semicrystalline, Thermoplastic Anhydrous Proton Exchange Membranes in Fuel Cells.

With the manipulation of surface charges and loadings, 1 nm super-acidic metal oxide clusters can co-crystallize with poly(ethylene glycol) (PEG) at molecular scale for thermoplastic anhydrous proton exchange membranes (PEMs). The coexistence of crystalline and amorphous regions endows the PEMs with a high Young's modulus and high flexibility, while the noncovalent complex interactions enable facile preparation and (re)processing. Furthermore, the diffusive dynamics of PEG chains is slowed by the confinement effect, while the local segmental dynamics is accelerated due to the transition of the chain conformation from helix to zigzag when confined in the crystalline framework. This greatly facilitates proton transportation in the crystalline region for an excellent anhydrous proton conductivity of 4.5 × 10 -3 S cm -1 at 90 °C. The balanced proton conductivity, mechanical strength, and processability of the PEMs contribute to the promising power density of H 2 /O 2 fuel cells assembled with co-crystalline PEMs at high temperatures under dry conditions.