Decoupling Segmental Dynamics and Ionic Transport for Superionic Anhydrous Proton Conductors of...

Superionic anhydrous proton conductors can be obtained from the complexation of nanoscale polyoxometalates (POMs) and poly(ethylene glycol) (PEG) in the "polymer in salt" regime. The reduced energy barrier of H⁺ hopping is facilitated from the increased H⁺ concentration and shortened inter-POM distances. POMs with identical structure/size (≈1 nm) but different charge densities are complexed with PEG, respectively, with concentrations ranging from 10 to 60 % wt. Increasing trends of viscosities can be observed with the rising charge densities of POMs due to the increasing confinement strength on PEG substrate from POMs. Fractional Walden rule is further applied to analyze the viscosity and proton conductivity correlations, and microscopic mechanisms of proton conduction for PEG-POM nanocomposites are revealed: 1) ion transport is highly associated with polymer chain dynamic for POMs concentrations ranging from 10 to 30 % wt.; 2) ionic conduction is largely decoupled from chain dynamic of polymer matrix for concentrations ranging from 40 to 60 % wt. with Walden plots shifted to the superionic regime. The decoupling of proton transport from polymer segment dynamics allows the simultaneous enhancements of the nanocomposites' mechanical properties and proton conductions, providing guidelines for the rational design of anhydrous proton conductors with integrated functionalities.